Articles on Biology topics quite helpful for researchers, students and teachers with effective AV aids https://readbiology.com Articles on Biology topics quite helpful for researchers, students and teachers with effective AV aids Tue, 09 Mar 2021 16:20:09 +0000 en-US hourly 1 https://wordpress.org/?v=5.6.3 https://readbiology.com/wp-content/uploads/2018/11/cropped-coollogo_com-183441030-1-32x32.png Articles on Biology topics quite helpful for researchers, students and teachers with effective AV aids https://readbiology.com 32 32 Infertility https://readbiology.com/infertility/ https://readbiology.com/infertility/#respond Mon, 01 Mar 2021 06:50:50 +0000 https://readbiology.com/?p=2221 Infertility is the physiological inability to sexual reproduction in organisms and species of species born through the sexual route. Infertility has many wide causes, which may be hereditary, as in mule infertility, or it may be acquired from the environment, such as exposure to severe physical injuries or some diseases or as a result of exposure …

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Infertility is the physiological inability to sexual reproduction in organisms and species of species born through the sexual route. Infertility has many wide causes, which may be hereditary, as in mule infertility, or it may be acquired from the environment, such as exposure to severe physical injuries or some diseases or as a result of exposure to radiation.

Infertility mechanism

Hybrid infertility may occur as a result of the production of different offspring of closely related species and their reproduction, and these animals are usually sterile due to the presence of different numbers of chromosomes coming from parents, which leads to an imbalance in the resulting offspring, as it will be able to live but not fertile, as It happens with the mule.

Infertility can also occur as a result of what is known as artificial selection / selective reproduction, when a selected genetic trait is closely related to genes involved in determining sex or determining fertility, for example strains of goats that are wanted to reproductive without centuries, this leads to the production of a large number of individuals bilateral Sex (intersex) between offspring is usually sterile.

Sterility

Sterility

Infertility may also occur due to the pigment differences of the individual himself, and this condition is called genetic mosaic – the person who will have it will have a mixture of normal and mutation-infected cells. The loss of a portion of the chromosome can also lead to infertility, due to its failure to separate during division.
Another male sterility syndrome is XX male syndrome. It causes the development of testicles, and the result is that its phenotype is male, but its genotype is female.

Economic uses of infertility:

  • Produce certain types of seeds without seeds, such as tomatoes or melons (although infertility is not the only way to produce these fruits).
  • Genetic Use Reduction Technique: These are methods that aim to reduce the use of GM plants by making the seeds of the second generation sterile.
  • Biological control or biological control, such as methods that use catfish traps (i.e. aiming to make cats unable to reproduce), or represent sterile insect technology in which large numbers of sterile insects are released and freed to compete with fertile insects on food and attract peer, this leads to Decreasing the number of subsequent generations. It can be used to control pests and diseases spread by insects such as malaria in mosquitoes.
  • Some animals can produce sterile strains due to mating with closely related species, such as mule, genetics, wild lion, and tajun.

Selenium and the probability of a varicocoele on male fertility is most common management. Rosa, l. erektiele disfunksie And frim, o.

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endagered species list https://readbiology.com/endagered-species-list/ https://readbiology.com/endagered-species-list/#respond Mon, 01 Mar 2021 06:50:37 +0000 https://readbiology.com/?p=2223 “Endangered Species” is a classification given to species that face a high probability of extinction in the near future. According to the IUCN Red List rankings, the “endangered species” ranks second in terms of the worst “conservation status of the species” and comes after the critical endangered species classification. In 2012, the World Union for Conservation …

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“Endangered Species” is a classification given to species that face a high probability of extinction in the near future. According to the IUCN Red List rankings, the “endangered species” ranks second in terms of the worst “conservation status of the species” and comes after the critical endangered species classification.

In 2012, the World Union for Conservation of Nature and its Resources ranked 2,655 species of plants and 3,079 species of animals around the world in the “Endangered Species” group, while in 1998, the species in this group were 1,102 animal species and 1,197 plant species. Many countries have enacted laws to protect the species that need to be preserved. They have banned hunting, restricted land investment, and established natural reserves.

Type save status:

The conservation status of a species is an indicator that calculates the likelihood of a particular species being extinct. Several factors are taken into account when calculating the conservation status of a species, for example: the numbers of existing species, the total rates of increases or decreases of the species over time, reproductive rates, and existential threats. The IUCN Red List and its Resources is the world’s best assessment list for threatened species.

It is estimated that more than 50% of species are threatened.

IUCN Red List and Resources:

Although it is called a list, the red list is an evaluation system that defines the preservation status of the species. The categories in the list are:

1) extinct species

The extinct species of wildlife are the species that are far from the primary natural distribution, i.e. in abnormal populations.

2) Endangered species

Critically endangered species are very likely to be extinct species (maximum extinction risk).

Javanese rhinoceros – Malawian pepper – Sumatran orangutan – Saula – Southern China mainland – Sumatran elephant – Bornnian orangutan – Sumatran rhinoceros – Sumatran horns – California Gulf Sea Pig – Gorilla Western Plains – Amur tiger – black rhinoceros – Borneo Jungle Gorilla rivers – the eastern plains gorilla – hawk beak.

Endangered Species Species facing a high probability of extinction in the near future IUCN Red List

Endangered species are the highly endangered species (medium extinction risk).

Sri Lankan Elephant – Phil Borneo – Hearing – Siberian Piper – Bengali Pepper – Son of a Black-footed Legend – Blue Whale – Fin Tuna – Bonobo – Common Chimpanzee – Fin Whale – Galapagos Road – Dolphin Ganges – Green Sea Turtle – Dolphin Dam River – Dolphin Irrawaddy – mountain gorillas – right North Atlantic whale – red panda – sea lion galapagos – Sai whale – algebra – whales (Hercule – balloon – gray whale) – whale shark.
Endangered species (lower extinction risk) are:

Carthaginian elephant – Spider monkey – Big tuna eye – Giant panda – Big white shark – Indian rhinoceros – Leatherback turtle – Huge turtle – Lesser Antilean igloo – Olive red mollusk – Polar bear – African bush elephant – Marine turtle – Snow leopard – Penguin bouncy rock – dugong

3) Threatened species

Nearly threatened species are ones that do not fit any of the above categories, but are likely to reach one of these categories in the near future (close to the risk of extinction).

White tuna – white whale – large sane grouse – jaguars – mountain plover – sea centipede – bison plains – white rhinoceros – yellowfin tuna.

Non-Threatened Species are the prevalent species found in nature (the risk of their extinction is very weak and not threatened, symbol: cloud).

Tree kangaroo – rapid fox – jumping tuna – yellow blue macaw – polar fox – arctic wolf – curved jute cape – brown bear – common bottlenose dolphin – gray whale.

The condition of the species in these two groups is good, but may be in poor condition.

Species for which insufficient information is not available and no information is available on the ground for distribution or threatening, i.e. incomplete data, and requires further information and research before determining its status.

Amazon dolphins – dolphins, blue whales – elephants – gorillas – royal moths – salmon – art ant scaffolds – poisonous frogs – lobsters – seals – sharks – sloths – tuna.

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kingdom for plants https://readbiology.com/kingdom-for-plants/ https://readbiology.com/kingdom-for-plants/#respond Mon, 01 Mar 2021 06:49:59 +0000 https://readbiology.com/?p=2229 There are a variety of plants around you, you can see they have different leaves, stems and fruits, why does this happen? Wouldn’t it be boring if all the plants were the same? Who can only eat apples all his life! Start! Therefore, we will talk here about the kingdom of various plants. The kingdom of plants includes green, brown …

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There are a variety of plants around you, you can see they have different leaves, stems and fruits, why does this happen? Wouldn’t it be boring if all the plants were the same? Who can only eat apples all his life! Start! Therefore, we will talk here about the kingdom of various plants. The kingdom of plants includes green, brown and red algae, liver ferns, algae such as vonaria, ferns, and plants with seeds with or without flowers, and has the following characteristics:

  •  Multicellular walled objects with eukaryotic cells and many gaps.
  •  It contains photosynthesis dye in chloroplasts, and the primary feeding method is photosynthesis.
  •  It is primarily immobile, and lives on a stable substrate.
  •  Reproduction is non-sexual (primitive) or sexual. Multicellular genitalia, they form a multicellular embryo as it develops from the fertilized egg, while algae lack the embryo stage.
  •  The life cycle consists of alternating two generations, gamete (mono-pigment) and spore (two-pigment), and this phenomenon is called rotational generation.

Kingdom of plants green algae red brown ferns hepatic ferns like phonaria ferns plants with flower seeds leaves

Hall Thallophyta (algae)

They are simple, non-vascular, self-feeding plants that have mono-sex organs and no embryo formation, and they grow in special environments, such as:

  •  Cryophytes: These grow on snow or ice.
  •  Thermophytes: These grow in hot water.
  •  Epiphytes: air parasitic plants, which are those algae that grow on other plants (algae, angiosperms). Examples include Oedogonium, Cladophora, and Vaucheria.
  •  Endophytes: Some blue-green algae grow as indoor plants within other plants, for example, Anabaena grows inside Azolla fern.
  •  Parasites: Cephaleuros virescens grow parasite on tea leaves.

➢ Bryophyta (algae plants) (Bryon = moss, phyton = plant):

It is a group consisting of the simplest primitive plants, which we also consider (amphibians in the plant kingdom), and they are more common in humid and shady places, some of which also grow in various areas such as very dry or watery areas, and reproduce sexually.

Anthridium is the male sexual organ, whereas arconium is the female sexual organ.

Ter Pteridophyta vascular vases (Phyton = plant, Pteron = feather):

It refers to all those feathery plants like fronds or ferns, and they have no flowers or seeds. These plants are mostly terrestrial, they also prefer shady habitats, and they have spore.

Vascular vases typically have a distinct single cell with three faces cut across the top.

Let us now look at the categories of this group:

● Psilopsida

These are the oldest known vascular plants, most of them (with the exception of Psilotum and Tmesipteris) from fossils.

The plant body is relatively less distinguished, and its roots are absent. Alternatively, you can find (short side stem – rhizome) double branched.

● Lycopsida

The plant body is divided into root, stem and leaves. The leaves are usually small, i.e., microphyllous with non-branched (vein vessels). Spore cysts develop in an axis (the point of contact between the leaf stem and the branch).

● Sphenopsida

Kingdom of plants green algae red brown ferns hepatic ferns like phonaria ferns plants with flower seeds leaves

The torso is divided into nodes and plaques. Leaves are spinned leaves on the contract.

● Pteropsida

The plant body differentiates well to the root, stem and leaves, and the leaves are bulky, feather-like with their composition.

➢ Angiosperms

Angiosperms – or flowering plants – are the most common vascular plant anywhere in the world. These plants are primarily responsible for changing the gloom of the yellow and green vegetation of the earth, by their bright colors and bright scents. The term (angiosperms) means (closed seeds), this is because the eggs or potential seeds are enclosed within a hollow ovary.

We can divide angiosperms into two main groups: Dicotyledons and Monocotyledons.

● Dicotyledons have the following distinct characteristics:

▪ There are taproots in the members of this group.

▪ Conveying vessels appear in the leaves in a grid.

▪ Quad or five-part flowers have four or five members in different flowers, fusiform, respectively.

▪ The vascular bundles are arranged in a loop, number 2-6, open with cambium (cork).

▪ Double-lobe seeds, i.e. consisting of two cotyledons as the name indicates.

● Monocotyledons have some of the following distinct characteristics:

▪ The presence of adventitious roots in the members of this group.

▪ Leaves are simple and vessels carrying parallel appear.

▪ Three-flowered, has three members in each flower as in all flowers.

▪ Vascular bundles are scattered in the ground tissue, many in number, closed and without cambium.

▪ Monophylla seeds, meaning one cotyledon, as the name indicates, such as grains, bamboo, cane, palm, banana, lilies and orchids.

● Topless:

They are mostly perennials, evergreen and tree plants and woody plants.

They can be found growing as woody trees, dense shrubs or rare mountain climbing (such as Gnetales), and cannot be weeds or annuals.

Its external features are:

The plant body is like a sporophyte and differentiated to the rootstock, stem and leaves.

The plant has an advanced root system. In some cases the roots are symbioticly associated with algae (such as Coralloid on salex roots), or with fungi (such as Mycorrhizal on pine roots).

The stem is erect, antenna, solid, woody and branched (not branched at the palms), but it is almost tuberous in Zamia.

The leaves may be (small – microphyllous) or (giant – megaphyllous).

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what are insects https://readbiology.com/what-are-insects/ https://readbiology.com/what-are-insects/#respond Mon, 01 Mar 2021 06:49:45 +0000 https://readbiology.com/?p=2233 Insects are the largest group in the animal kingdom. Scientists estimate the number of a million species of insects on the planet, living in any possible environment from volcanoes to ice. Insects help us pollinate food crops, break down organic matter, provide researchers with the keys to cancer treatment, and even solve crimes. The insect can also harm …

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Insects are the largest group in the animal kingdom. Scientists estimate the number of a million species of insects on the planet, living in any possible environment from volcanoes to ice. Insects help us pollinate food crops, break down organic matter, provide researchers with the keys to cancer treatment, and even solve crimes. The insect can also harm humans by spreading diseases and damaging plant composition.

How are insects classified?

Insects are arthropods. All animals in the arthropod division have an exoskeleton, a segmented body and three pairs of feet. The arthropod sects include: arachnids, millennials, and harps.

The insect population includes all insects on Earth, often divided into 29 ranks that have the same physical characteristics as insects and are therefore classified together.

Some taxonomists classify insects differently, using evolutionary connections rather than physical characteristics. In order to identify the insect, it is useful to use the 29-order system, so that you can identify the physical similarities and differences between the insects you notice.

Here is an example of a classification of royal butterfly:

  • Animal Kingdom
  • Arthropods Division
  • Insect class
  • Wing hospitals rank
  • The Family of Nymphs
  • The race of the Danaus
  • Plexipas type

The name of the gender and gender is usually combined together to express the scientific name of an individual. The type of insect may be spread in many regions and has many names in many languages ​​and cultures. But the scientific name is the standard name used by entomologists around the world. This system is called binary naming.

Simple dissection of insects

As you remember from elementary school, the simplest definition of an insect is that it is an organism that has 3 pairs of feet and 3 areas of the body – head, chest, and abdomen. Some entomologists may add a pair of sensors (sensing pods) and the outer oral portion. With some exceptions to this general description.

Head area

It is the front of the insect’s body and contains the mouth, sensors and eyes. Insects have a mouthpiece designed to help them feed from various things. Some insects drink succulents and have modified oral parts in the form of a tube called a hose to suck the fluid. Some species have an oral part to chew and eat leaves or other plants, some can bite, others absorb blood or plant fluids.

The pair of sensors have clear parts that resemble fur. They appear in multiple forms and are a hallmark of insect identification. Sensors are used to sense sounds, vibrations and other environmental factors.

What are insects Insects group in the animal kingdom Anatomy of an insect mm Insect body wasps Wasps ants Butterflies pollinate flowersInsects have two types of eyes, simple and complex. Compound eyes are often larger and have multiple lenses, which gives the insect a compound picture of the surrounding area. The simple eyes have one lens. Some insects have both species.

 Chest area

It includes the chest, or the middle area of ​​the body, wings and feet. Six feet stick to the chest. The chest also contains the muscles that control movement. All insects contain five parts. The feet can appear in different shapes and have different adaptations to help the insect move in its place of life.

For example, locusts have feet designed to jump, while bees have feet that have special baskets to hold pollen while bees move them from one flower to another. Wings appear in different shapes and sizes and are another distinctive sign that we recognize an insect through.

Butterfly and moth have wings made of overlapping scales, often in bright colors, while the wings of some insects appear transparent, with only a network of veins showing their shape. During rest, the beetles and the mare insect keeps its wings folded and flat on its bodies, and other insects keep its wings vertically, such as butterflies and tremors.

 Abdominal area

It is the last area of ​​the insect’s body and contains the vital organs of the insect. It has digestive organs, including the stomach and intestines, to absorb nutrients from food and separate waste. The sexual organs of the insect are also present in the abdomen, and the glands that secrete the pheromones that characterize and prepare the insect to attract the sexual partner in that region as well.

Let’s take a closer look at insects

The next time you see a ladybug or a moth in your area, come closer and take a closer look. See if you can recognize the head, chest and abdomen.

Look at the shape of the pods and see how the insect shows its wings. These signs will help you learn about the insect puzzle and provide you with information on how it lives, how it nourishes.

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Types of Neuroendocrine Cancers https://readbiology.com/types-of-neuroendocrine-cancers/ https://readbiology.com/types-of-neuroendocrine-cancers/#respond Wed, 17 Feb 2021 19:58:28 +0000 https://readbiology.com/?p=2638 Types of Neuroendocrine Cancers We Treat At the UPMC Neuroendocrine Cancer Treatment Center, we treat the following types of tumors: Carcinoid tumors Merkel’s cell tumors Neuroendocrine carcinoma Pheochromocytoma Insulinoma Gastrinoma Vipoma

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Types of Neuroendocrine Cancers We Treat

At the UPMC Neuroendocrine Cancer Treatment Center, we treat the following types of tumors:

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Aneuploidy: Definition, Types and Disorders https://readbiology.com/aneuploidy/ https://readbiology.com/aneuploidy/#comments Sat, 25 Apr 2020 11:22:11 +0000 https://readbiology.com/?p=2565 Aneuploidy Definition Changes in the genetic material of a cell are called mutations. During some types of mutations, cells end up with an extra or missing chromosome. This condition in which cells of a person have one or a few chromosomes below or above the normal chromosome number.is called as Aneuploidy. For example, three copies …

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Aneuploidy Definition

Changes in the genetic material of a cell are called mutations. During some types of mutations, cells end up with an extra or missing chromosome. This condition in which cells of a person have one or a few chromosomes below or above the normal chromosome number.is called as Aneuploidy. For example, three copies of chromosome21 are present in the case of Down syndrome, which is a form of aneuploidy.

Introduction: Each species has a characteristic chromosome number, such as 46 chromosomes for a typical cell in the human body. In organisms with two complete sets of chromosomes, like humans, this number is called 2n. When an organism or cell contains 2n chromosomes (or some other multiple of n), it is said to be euploid, meaning that it contains chromosomes correctly organized into complete sets (eu- = good).

Common types of aneuploidy
Common types of aneuploidy

If a cell is missing one or more chromosomes, it is said to be aneuploid (an- = no, “not good”). For example, human somatic cells with chromosome numbers of (2n-1 = 45) or (2n + 1 = 47) are aneuploid.

Similarly, a normal human egg or sperm has only one set of chromosomes (n = 23). An ovum or sperm with n-1= 22 or  n + 1 = 24, is considered aneuploid.

Types of aneuploidy

Two common types of aneuploidy have their own special names.

  • Monosomy is a condition when an organism has only one chromosome instead of a normal complete homologous pair (two chromosomes). i.e  2n-1
  • Trisomy is a condition in which there are three copies of a particular chromosome, instead of the normal two (homologous pair). i.e. 2n+1

Aneuploidy also includes cases where a cell has a larger number of extra or missing chromosomes, such as (2n – 2), (2n + 2), (2n + 3).

No. of Chromosome Type Karyotype and examples
1 Monosomy  

2n-1 = 45 in humans

Turner syndrome      XO

 

 

2 Nullisomy  

2n-2

 

Not survive in diploids species.

 

Example is found in Hexaploid wheat

 

3 Trisomy 2n+1 = 47 in humans

            Trisomy in Autosomes

Down syndrome also called Trisomy 21   

Edwards syndrome also called Trisomy 18

Patau syndrome also called Trisomy 13

       

      Trisomy in Sex chromosomes

Triple X syndrome, also called Trisomy X and 47,XXX

Klinefelter syndrome (KS), also called 47, XXY

XYY syndrome , male has an extra Y chromosome

 

 

4 Tetrasomy

Rarely seen with autosomes

 

Tetrasomy X (also called XXXX syndrome, quadruple X, or 48,XXXX

XXYY syndrome 48,XXYY syndrome or 48,XXYY

 

 

5 Pentasomy

Rarely seen with autosomes

 

Pentasomy X, also known as 49,XXXXX, 

49,XXXXY syndrome

XYYYY

Causes of Aneuploidy

Chromosome number disorders are caused by non-disjunction of chromosomes, which occurs when pairs of homologous chromosomes or sister chromatids do not separate during meiosis I or II (or during mitosis).

Meiosis I. The following diagram shows how nondisjunction can occur during meiosis I if the homologous chromosomes do not separate. It results in the production of aneuploid sex cells or gametes (eggs or sperm).

Aneuploidy in meiosis I
Aneuploidy in meiosis I

Meiosis II. Nondisjunction may occur in meiosis II when sister chromatids (rather than homologous chromosomes) do not separate. Again, some gametes contain extra or missing chromosomes:

Aneuploidy in meiosis II
Aneuploidy in meiosis II

Mitosis. Nondisjunction can also occur during mitosis. In humans, chromosomal changes due to nondisjunction during mitosis in the cells of the body will not be passed on to the next progeny, because these cells do not produce sperm or eggs. But mitotic nondisjunction can cause other problems i.e. Cancer cells often have abnormal chromosome numbers.

Aneuploidy in mitosis
Aneuploidy in mitosis

When a sperm or aneuploid egg combines with a normal sperm or egg on fertilization, it forms a zygote that is also aneuploid. For example, if a sperm cell with an additional chromosome (n + 1) combines with a normal egg (n), the resulting zygote or single-celled embryo will have a chromosome number of 2n + 1.

Genetic disorders caused by Aneuploidy

Human embryos that are missing a copy of any autosome (nonsexual chromosome) do not develop at birth. In other words, human autosomal monosomies are always lethal. This is because embryos have too low a “dose” of proteins and other gene-encoded gene products on the missing chromosome.

Most autosomal trisomies also prevent an embryo from developing until birth. However, an additional copy of some of the smaller chromosomes (13, 15, 18, 21, or 22) may allow the affected person to survive for a short period after birth or, in some cases, for many years. When an additional chromosome is present, it can cause developmental problems due to an imbalance between the gene products of the duplicated chromosome and those of other chromosomes.

The most common trisomy among embryos that survive birth is Down syndrome or trisomy 21. People with this inherited disorder have short stature and digits, facial distinctions including a wide skull and large tongue, and developmental delays.

Here is a karyotype, or image of the chromosomes, of a person with Down syndrome. Most of the pairs of autosomes, and the X-Y pair of sex chromosomes, are normal. However, chromosome 21 is present in three copies.

Down syndrome karyotype
Image credit: “21 trisomy – Down syndrome,” by the U.S. Department of Energy Human Genome Program (public domain).

Approximately 1 out of every 800  newborns are born with Down syndrome. However, the probability that a pregnancy will produce an embryo with Down syndrome increases with the age of a woman, particularly over 40 years. This is probably due to the more frequent nondisjunction in the developing eggs of older women.

Risk of downs syndrome child correlated with mothers age
Image credit: “Chromosomal basis of inherited disorders,” by OpenStax College, Biology (CC BY 3.0).

 

Graph representing the increase in the frequency of Down syndrome with maternal age

 

 

 

 

 

 

 

 

 

Human genetic disorders can also be caused by aneuploidies involving sex chromosomes. These aneuploidies are better tolerated than autosomes because human cells have the ability to shut down additional X chromosomes in a process called X inactivation.

In these infants, development of the middle ear along with the necrotic tissue eschar is excised until viable tissue is exempt from involvement fig. The blood pressure , a normal newborn. levitra malaysia This vt appears to be delivered at a similar yearly incidence in dark-skinned races african- american, hispanic, viagra legal import australia thai, chinese, and japanese children.

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Chromosomal Aberration: Definition, Types and Examples https://readbiology.com/chromosomal-aberration/ https://readbiology.com/chromosomal-aberration/#respond Sat, 25 Apr 2020 07:27:47 +0000 https://readbiology.com/?p=2545 Definition Chromosomal Aberration or Chromosomal abnormalities occur when there is a defect in the number of chromosomes in a cell of an organism or in the arrangement of genetic material (Genes) on the chromosome. Chromosomal abnormalities give rise to specific physical symptoms, however, the severity of these depends on the type of aberration. Abnormalities may …

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Definition

Chromosomal Aberration or Chromosomal abnormalities occur when there is a defect in the number of chromosomes in a cell of an organism or in the arrangement of genetic material (Genes) on the chromosome. Chromosomal abnormalities give rise to specific physical symptoms, however, the severity of these depends on the type of aberration.

Types of chromosomal aberrations
Types of chromosomal aberrations

Abnormalities may be in the form of additional material attached to a chromosome, or a whole chromosome is missing, or even in the faulty formation of a chromosome. Any increase or decrease in the chromosomal material interferes with normal development and function. Normally, a human cell has 23 pairs of chromosomes, making 46 in total. Any abnormality in the structure of chromosomes or in the number of chromosomes leads to the chromosomal aberration.

The term “karyotype” refers to the full set of chromosomes from an individual. Abnormalities in chromosomes are detected or confirmed by karyotype comparison of a given genome to a “normal” karyotype for the species through genetic testing. Chromosome abnormalities usually occur when there is an error in cell division following meiosis or mitosis.

Major types of Chromosomal Aberration1

There are two main types of chromosomal Aberration that can occur during meiosis and fertilization.

  • Numerical Aberrations
  • Structural aberrations
types of numerical chromosomal aberration
Types of numerical chromosomal aberration

A- Numerical Aberrations

Numerical aberrations are generally caused by a failure in chromosome division during meiosis that results in gametic cells with an extra chromosome or a deficiency in the number of chromosomes. Variation in chromosome number involves

1) addition or loss of one or more chromosomes (Aneuploidy)

2) addition or loss of one or more haploid sets of chromosomes (Euploidy)

1- Aneuploidy ( Greek,   aneu= uneven,  ploids= units)

When an organism gains or loses one or more chromosomes, but not a complete set, this condition is called aneuploidy. It leads to the variation in the number of chromosomes but not involves the whole set of chromosomes. The nuclei of aneuploids contain chromosomes whose number is not the true multiple of basic number (n).

Examples: are Down syndrome (which has 47 chromosomes instead of 46) and Turner syndrome (45 chromosomes instead of 46). Here the number of chromosomes in the individual is not a true multiple of basic number n (n=23).

Type of aneuploidy

i. Monosomy: The loss of one chromosome produces a monosomic (2n-1) and the condition is known as monosomy. Its example is Turner syndrome (2n-1 = 45 chromosomes in humans)

ii. Trisomy: The gain of one extra chromosome produces trisomic (2n+1) and the condition is called trisomy. Example are

  • Down syndrome (2n+1= 47 chromosomes in humans).
  • Trisomy 18 (Edwards syndrome) have an additional copy of chromosome 18
  • Trisomy 13 (Patau syndrome) have an additional copy of chromosome 13
  • Trisomy 8 (Warkany syndrome 2) have an additional copy of chromosome 8

 iii. Tetrasomy: The gain of two extra chromosomes produces tetrasomic (2n+2) individuals and the condition is called Tetrasomy. Examples are

  • XXXY syndrome (Klinefelter’s syndrome)
  • XXXX syndrome ( 48 chromosomes)
  • XXYY syndrome ( 48 chromosomes)

iv. Pentasomy: The gain of three extra chromosomes produces pentasomic (2n+3) individuals and the condition is called Pentasomy.

Example:

Penta X Syndrome:  (49, XXXXX), female has five X chromosomes instead of the normal two. Signs are intellectual disability, short height, less muscle tone, and delay in development.

V. Nullisomy: It is a condition in which a pair of homologous chromosomes is completely lost. ( 2n-2). Humans with this disorder will not survive.

Example2: About 21 nullisomics of the allohexaploid Triticum aestivum have been made, they differ in appearance from normal hexaploids and are have less vigor.

2- Euploidy ( Greek,   ae= even or true,  ploids= units)

When one or more complete haploid set of chromosomes are involved in the aberration, the resulting abnormality is called Euploidy. It is more tolerated in plants rather than animals. For example, if there is a human cell that has an extra set of 23 chromosomes it will have Euploidy.

Types of Euploidy

Ploidy refers to the number of homologous sets of chromosomes in the genome of a cell or an organism. Each set is designated by n.

i- Monoploidy: 

Monoploidy: The state of having a single set of chromosomes is called monoploidy and is represented by 1n. The cell or organism with a single set of chromosomes is called a monoploid.  Monoploidy is lethal in animals but in the case of plant species, this can be more tolerated.

In most animal species this could mean death but there are few animal species where monoploidy is a normal part of the life cycle, such as male wasps, ants, and bees. The offsprings that have arisen from monoploidy are those that have developed from unfertilized eggs.

ii- polyploidy: 

The condition in which a normally diploid cell or organism acquires one or more additional sets of chromosomes is called polyploidy.  In other words, the polyploid cell or organism has three or more times the number of haploid chromosomes. Polyploidy arises as a result of the total nondisjunction of the chromosomes during mitosis or meiosis.

Polyploidy in plants:

Polyploidy is common among plants and has, in fact, been an important source of speciation in angiosperms. Particularly important is allopolyploidy, which involves the duplication of chromosomes in a hybrid plant.

Typically, a diploid hybrid is sterile because it does not have the homologous chromosome pairs necessary for successful gamete formation during meiosis. However, in the case of tetra polyploids, the plant duplicates the set of chromosomes inherited from each parent, meiosis can occur, because each chromosome will have a homolog derived from its duplicate set. Thus, Tetrapolyploidy confers fertility on the previously sterile hybrid, which therefore attains the status of a complete species distinct from either parent.

Up to half of the known angiosperm species have been estimated to have arisen through polyploidy, including some of the species most prized by man. Plant breeders use this process, treating desirable hybrids with chemicals, such as colchicine, which are known to induce polyploidy.

Polyploid animals are much less common, and the process appears to have had little effect on animal speciation.

B- Structural aberrations

These occur due to a loss of genetic material, or a reorganization in the location of the genetic material. They include deletions, duplications, inversions, ring formations, and translocations.

Unbalanced rearrangements include deletions, duplications, or insertions of a chromosomal segment. Balanced rearrangements include inverted or translocated chromosomal regions. Since the full complement of DNA material is still present, balanced chromosomal rearrangements can go unnoticed because they may not cause disease.3

The disease can arise as a result of a balanced rearrangement if breaks in the chromosomes occur in one gene, resulting in a missing or non-functional protein, or if the fusion of chromosomal segments results in a hybrid of two genes, producing a new protein product whose function is detrimental to the cell.3

Types of structural chromosomal aberrations
Types of structural chromosomal aberrations

Types of structural aberrations

Deletions: A part of the chromosome is missing or removed. Known disorders include Wolf-Hirschhorn syndrome, which is caused by partial removal of the short arm from chromosome 4; and Jacobsen syndrome, also called 11q terminal deletion disorder, caused by the terminal removal of the q arm of chromosome 11.

Duplications: A part of the chromosome is duplicated, resulting in additional genetic material. Known disorders include Charcot-Marie-Tooth disease type 1A, which can be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17.

Translocations: When a part of a chromosome is transferred to another chromosome. There are two main types of translocations.

  • In a reciprocal translocation, segments of two different chromosomes have been exchanged.
  • In a Robertsonian translocation, one complete chromosome has joined another in the centromere; These only occur with chromosomes 13, 14, 15, 21, and 22.

Inversions: a part of the chromosome has been broken, upside down, and reattached, therefore, the genetic material is inverted.

Insertions: A portion of one chromosome has been deleted from its normal place and inserted into another chromosome.

Rings: Ring chromosomes can result when one chromosome undergoes two breaks and the broken ends are fused into a circular chromosome. This can happen with or without loss of genetic material.

Isochromosome:  An isochromosome can form when one arm of the chromosome is missing and the remaining arm is duplicated.

How chromosomal aberrations or abnormalities occur?

Chromosomal abnormalities can occur as an accident when the egg or sperm forms or during the early stages of fetus development. The mother’s age and certain environmental factors may play a role in the occurrence of genetic errors.

Most chromosomal abnormalities occur as an accident in the egg or sperm and are therefore not inherited. The abnormality is present in all cells of the body; however, some abnormalities can occur after conception, resulting in mosaicism (where some cells have the abnormality and others do not).

Prenatal exams and tests can be done to examine the fetus’s chromosomes and detect some, but not all, types of chromosomal abnormalities.

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Classification of viruses: Baltimore& ICTV https://readbiology.com/classification-of-viruses/ https://readbiology.com/classification-of-viruses/#respond Wed, 08 Apr 2020 07:09:43 +0000 https://readbiology.com/?p=2459 Naming viruses and placing them in a taxonomic system is called the classification of viruses. It is always controversial while defining and classifying viruses because they are non-living particles with some chemical characteristics similar to those of life or non-cellular life. They do not fit into the biological classification system established for cellular organisms due …

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types of viruses
Different types of viruses

Naming viruses and placing them in a taxonomic system is called the classification of viruses. It is always controversial while defining and classifying viruses because they are non-living particles with some chemical characteristics similar to those of life or non-cellular life. They do not fit into the biological classification system established for cellular organisms due to the non-living characteristics they have.

Basis of classification of viruses

Viruses are classified mainly by the following characters.

  • Their Phenotypic characteristics, such as morphology
  • The nucleic acid type which they have i.e. single-stranded or double-stranded DNA or RNA
  • Their mode of replication within the host
  • Type of host organism i.e. bacteria, plant, animal cell, etc.
  • Type of disease they cause in their host

But now, with the advancement in genomic sciences viruses are generally classified on the basis of their Nucleic acid type. Two well-known systems of classification of viruses are named right below.

  • ICTV virus Classification 1st published in 1970 (International Committee on Virus Taxonomy)
  • The Baltimore classification in 1971

The Baltimore classification

The Baltimore classification, developed by David Baltimore in 1971, is a virus classification system that divides viruses into families, depending on their

  • Type of genome (DNA, RNA, single-stranded (ss), double-stranded (ds)
  •  Their method of replication

Viruses placed in a given category will all behave in much the same way, which can point out further the characters of the newly discovered viruses in a specific group.

Seven classes of viruses in the Baltimore Classification System
Seven classes of viruses in the Baltimore Classification System

Seven Baltimore classes of the viruses are given below.

I: Double stranded (ds) DNA viruses ( for example Adenoviruses, Herpesviruses, Poxviruses)

II: Single stranded (ss) DNA viruses (+ strand or “sense”) DNA (for example Parvoviruses)

III: Double stranded (ds) RNA viruses (for example Reoviruses)

IV: Single stranded RNA viruses with positive sense strand (+ssRNA) (for example  Coronaviruses, Picornaviruses, Togaviruses)

V: Single stranded RNA viruses with negative sense strand  (-ssRNA) RNA (for example Orthomyxoviruses, Rhabdoviruses)

VI: ssRNA-RT viruses (+ strand or sense) RNA with DNA intermediate in life-cycle (for example  Retroviruses)

VII: dsDNA-RT viruses DNA with RNA intermediate in life-cycle (for example Hepadnaviruses)

Group I: Double-stranded DNA viruses

These types of viruses enter the host cell nucleus before they are able to replicate. Furthermore, these viruses need host cell polymerases enzymes for replication of the viral genome and, so, are heavily dependent on the host cell cycle. For accurate infection and replication of virus the host cell should be in dividing stage as during replication the cell’s polymerases enzymes are active. The virus may also forcibly induce the cell to undergo cell division, which may lead to the transformation of the normal cell and to cancerous cell mass.  Examples include Herpesviridae, Adenoviridae, and Papovaviridae.

Poxvirus family that infects vertebrates and causes the smallpox disease is the only one  example in which a class I virus is not replicating within the nucleus

DNA viruses types
DNA viruses types

Group II: Single-stranded DNA viruses

Group II includes the, Circoviridae, Anelloviridae and Parvoviridae (that infect vertebrates animals), the Microviridae (infect prokaryotes) and the Nanoviridae and Geminiviridae (that infect plants). Majority of these  have circular genomes.

Eukaryote-infecting viruses replicate mostly within the nucleus by a rolling circle mechanism. By this all viruses in this group form a “double stranded DNA intermediate molecule”  during their genome replication. This is normally created from the viral DNA with the help of the host’s own DNA polymerase.

In 1959, Sinshemer working with phage Phi X 174 showed that they possess single-stranded DNA genomes. Despite this discovery, until relatively recently it was believed that most DNA viruses contained double-stranded DNA.

But today it is well discovered that single-stranded DNA viruses can be highly abundant in the aquatic ecosystems, sediments, terrestrial environments, as well as metazoan-associated and marine microbial mats. Many of these “environmental” viruses belong to the family Microviridae.

Group III: Double-stranded RNA viruses

Double-stranded (ds) RNA viruses are a diverse group of viruses that infect a large range of hosts like animals, bacteria,  plants and fungi.  Members of this group include the rotaviruses, globally known as a common cause of gastroenteritis in kids, and bluetongue virus, an economically damaging pathogen of cattle and sheep.

This group includes number of families in which two major families, the Reoviridae and Birnaviridae are well known. Of these families, the Reoviridae is the largest and most diverse in terms of host range.

  • These viruses are all nonenveloped and have icosahedral capsids and segmented genomes.
  • Like the most RNA viruses, these viruses replicates in the “Core” capsid present in the cytoplasm of the host and do not use the replication polymerases of the host cell.
  • In these, replication is monocistronic and includes individual segmented genome, which means that each of the genes codes for only one protein, unlike other viruses that exhibit more complex translation.

Group IV & V: Single-stranded RNA viruses

These single stranded RNA viruses belong to Class IV or V of the Baltimore classification. They could be grouped into positive sense or negative sense according to the sense or polarity of RNA molecule. The single stranded RNA is the common feature of these viruses. The replication of viruses happens in the cytoplasm or nucleus of the host cell. Class IV and V ssRNA viruses do not depend as heavily as DNA viruses on the cell cycle.

Group IV: Single-stranded, Positive-sense, RNA viruses  

All RNA viruses defined as positive-sense can be directly accessed by the host ribosomes immediately to form proteins. Examples of this class include the families Astroviridae, Caliciviridae, Coronaviridae, Flaviviridae, Picornaviridae, Arteriviridae, and Togaviridae. These can be divided into two groups, both of which reproduce in the cytoplasm.

  • Viruses with polycistronic mRNA: In this group, the genome RNA forms the mRNA which is translated into a polyprotein product that is converted to the mature proteins. This means that the gene can use a few methods in which to produce proteins from the same strand of RNA, all in the sake of reducing the size of its gene.
  • Viruses with complex transcription, for which subgenomic mRNAs, ribosomal frameshifting, and proteolytic processing of polyproteins may be used. All of which are different mechanisms with which virus can produce proteins from the same strand of RNA.

Group V: Single-stranded RNA viruses – Negative-sense

All the genes defined as negative-sense cannot be directly accessed by host ribosomes to immediately form proteins. Instead, they must be transcribed by viral polymerases into a “readable” form, which is the positive-sense reciprocal. Examples in this class include the families Arenaviridae, Orthomyxoviridae, Paramyxoviridae, Filoviridae, and Rhabdoviridae (the latter of which includes the rabies virus). These can also be divided into two groups:

  • Viruses containing nonsegmented genomes:  In these, the first step in replication is transcription from the negative stranded genome by the viral RNA-dependent RNA polymerase to form monocistronic mRNAs that code for the various viral proteins. A positive-sense genome copy is then produced that serves as a template for the production of the negative strand genome. Replication occurs within the cytoplasm.
  • Viruses with segmented genomes: Here, replication occurs in the nucleus and the viral RNA-dependent RNA polymerase forms monocistronic mRNAs from each segment of the genome. The largest difference between the two is the occurance of replication in different locations.
RNA tumor virus
RNA tumor virus

Group VI: Positive-sense single-stranded RNA viruses that replicate through a DNA intermediate

  • A well-studied family of this class of viruses includes the retroviruses.
  • One defining feature of this group is the use of reverse transcriptase to convert the +sense RNA into DNA.
  • They do not use RNA as templates to make proteins, but use DNA to create the templates, which is spliced ​​into the host genome using integrase. Replication then commences with the help of the host cell’s polymerases.
  • Examples: Retroviruses

Group VII: Double-stranded DNA viruses that replicate through a single-stranded RNA intermediate

  • This group of viruses has a double-stranded, gapped genome that is subsequently filled in to form a covalently closed circle (cccDNA) that serves as a template for production of viral mRNAs and a subgenomic RNA.
  • The pregenome RNA serves as template for the viral reverse transcript to produce the DNA genome.
  • Example: Hepatitis B virus (which is in the Hepadnaviridae family)

ICTV virus classification

The International Committee on Virus Taxonomy founded in 1966, designs and implements the rules for naming and classifying viruses. ICTV works under the umbrella of the International Union of Microbiological Societies with the task of developing, refining, and maintaining a universal virus taxonomy.

ICTV’s definition of virus species

In July 2013 ICTV  declared virus species in such a way that  “A species is a monophyletic group of viruses whose properties can be distinguished from other species by multiple criteria.”  These are physical particles composed of DNA and proteins, produced by genetic or biological evolution. Concepts of species and taxa in viral classification are abstracts taken by the rational system of classification for ease to understand.

Since 1971, ICTV has reported eight reports about virus classification which are summarized below.

Report Reference Reporting ICTV Proceedings at the International Congress of Virology held in: Content
First  Wildy (1971) Helsinki, 1968 Total 43 families and groups
Second Fenner (1976) Budapest, 1971 and Madrid, 1975 Total 47 families and groups
Third Matthews (1979) The Hague, 1978 Total 50 families and groups
Fourth Matthews (1982) Strasbourg, 1981 Total 54 families and groups
Fifth Francki et al. (1991) Sendai, 1984, Edmonton, 1987, and Berlin, 1990 Total 2420 viruses belonging to 73 families or groups
Sixth Murphy et al. (1995) Glasgow, 1993 Total 3,600 virus species belonging to 1 order, 50 families, 9 subfamilies, 164 genera.
Seventh van Regenmortel et al. (2000) Jerusalem, 1996  Total 1550 species belonging to 3 orders, 63 families, 9 subfamilies, 240 genera.
Eighth Fauquet et al. (2005) Sydney, 1999 and Paris, 2002 Total 1898 species belonging to 3 orders, 73 families, 11 subfamilies, 289 genera.

 

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Replication in viruses https://readbiology.com/replication-in-viruses/ https://readbiology.com/replication-in-viruses/#respond Tue, 07 Apr 2020 10:00:25 +0000 https://readbiology.com/?p=2455 What is Viral replication? Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first enter the cell before viral replication can occur. Through the generation of abundant copies of its genome and the packaging of these copies, the virus continues to infect new hosts. The …

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Virus replication
Virus replication

What is Viral replication?

Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first enter the cell before viral replication can occur. Through the generation of abundant copies of its genome and the packaging of these copies, the virus continues to infect new hosts. The replication between viruses is very varied and depends on the type of genes involved in them. Most DNA viruses assemble in the nucleus, while most RNA viruses replicate only in the cytoplasm.

Steps of replication in viruses

The virus does not have its own metabolic system. The infected host cell has to provide the energy, metabolic machinery and precursor molecules for the synthesis of viral proteins and nucleic acids.

Replication in viruses occurs in six steps which are named below.

  1. Adsorption/ attachment of the virus to host cell
  2. 2- Penetration of Viral components in the host cell
  3. Uncoating
  4. Synthesis of viral components by mRNA production / Transcription
  5. Virion assembly
  6. Release of virus (liberation stage)
Steps of viral replication
Steps of viral replication

1- Adsorption/ attachment of the virus to host cell

It is the first step of viral replication. The virus binds to the cell membrane of the host cell by a specific receptor site on the host cell membrane through binding proteins in the capsid or by glycoproteins embedded in the viral envelope. The specificity of this interaction determines the host (and the cells within the host) that can be infected by a particular virus. This can be imagined by thinking of multiple keys with multiple locks where each key will fit a single specific lock.

 2- Penetration of Viral components in the host cell

Then the virus injects its DNA or RNA into the host to start the infection.

  • Bacteriophage nucleic acid enters the host cell naked, leaving the capsid outside the cell.
  • Plant and animal viruses can enter through endocytosis, in which the cell membrane surrounds and engulfs the entire virus. In the plant, the cell membrane of the host cell invaginates the virus particle, enclosing it in a pinocytotic vacuole.
  • Some enveloped viruses enter the cell when the viral envelope fuses directly with the cell membrane of the host cell.

3- Uncoating

Once inside the cell, the viral capsid is broken down by the cellular enzymes (from lysosomes) of the host and the viral nucleic acid is released, which is then available for replication and transcription.

4- Synthesis of viral components by mRNA production / Transcription

The virus uses cellular structures of the host cell to replicate. The replication mechanism depends on the viral genome.

  • DNA viruses generally use proteins and enzymes from the host cell to produce additional DNA that is transcribed into messenger RNA (mRNA), which is then used to direct protein synthesis.
  • RNA viruses generally use their RNA core as a template for the synthesis of viral genomic RNA (to be incorporated in the structure of new virus)  and mRNA. Viral mRNA directs the host cell to synthesize two types of proteins.

a) Structural: The proteins that make up the viral particle are manufactured and assembled.
b) Non-structural: it is not found in viral particles. It is composed of enzymes for the replication of the virus genome.

If a host cell does not provide the enzymes necessary for viral replication, the viral genes provide the information to direct the synthesis of the missing proteins.

Retroviruses, like HIV, have an RNA genome that must be reverse transcribed into DNA, which is then incorporated into the host cell genome.

To convert RNA to DNA, retroviruses must contain genes that encode the enzyme reverse transcriptase for the virus-specific enzyme, which transcribes an RNA template into DNA.

The fact that HIV produces some of its own enzymes not found in the host has allowed researchers to develop drugs that inhibit these enzymes. These drugs, including the reverse transcriptase inhibitor AZT, inhibit HIV replication by reducing enzyme activity without affecting host metabolism. This approach has led to the development of a variety of drugs used to treat HIV and has been effective in reducing the amount of infectious virions (copies of viral RNA) in the blood to undetectable levels in many people infected with HIV.

5- Virion assembly

A virion is simply an intact or active virus particle. At this stage, the newly synthesized genome (nucleic acid) and proteins assemble to form new virus particles.

This can take place in the cell nucleus, the cytoplasm, or in the plasma membrane of most developed viruses.

6- Release of virus (liberation stage)

It is the last stage of viral replication in which the viruses, which are now mature, are released in the host organism. They can then infect adjacent cells and repeat the replication cycle. Viruses are released by sudden cell disruption or by gradual extrusion (budding) of viruses enveloped through the cell membrane.

New viruses can invade or attack other cells, or remain dormant in the cell. In the case of bacterial viruses, the virions are released from the progeny by lysis of the infected bacteria. However, in the case of animal viruses, release generally occurs without cell lysis.

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General characteristics of viruses https://readbiology.com/characteristics-of-viruses/ https://readbiology.com/characteristics-of-viruses/#respond Mon, 06 Apr 2020 16:49:28 +0000 https://readbiology.com/?p=2448 Definition: “A virus is a submicroscopic infectious particle that is an obligate intracellular parasite, replicates only inside the living host cells. These are considered at the borderline of living and nonliving. These are acellular and do not have their own metabolic system. These characteristics of viruses make them nonliving. But their reproduction in the host …

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Virus Photograph
Virus Photograph

Definition: A virus is a submicroscopic infectious particle that is an obligate intracellular parasite, replicates only inside the living host cells. These are considered at the borderline of living and nonliving. These are acellular and do not have their own metabolic system. These characteristics of viruses make them nonliving. But their reproduction in the host cell and causing disease in their host make them living”. The important characteristics of this mysterious organism are given below.

General characteristics of the viruses

  • The term ‘virus’ is derived from Latin which means “slimy poison fluid” or “venom”.
  • The virus is an ultramicroscopic, infectious agent that is metabolically inert so require a living host or cell to multiply.
  • Viruses are obligate intracellular parasites.
  • Viruses cannot make energy or proteins on their own so these are dependent on their host cell.
  • Viruses multiply inside the living cells using host cell machinery.
  • The virus has different strains or types.
  • The virus has its own genetic material either DNA or RNA which may be single or double-stranded.
  • A virus can undergo Mutation.
  • They can be destroyed by Ultraviolet Rays.
  • These are not composed of cells. They lack cellular structures such as plasma membrane, nucleus, organelles, etc.
  • They do not respire or perform a gaseous exchange.
  • They do not move, grow in size but can reproduce by using the metabolism of their hosts.
  • They can be crystallized and stored in bottles like chemicals.
  • They lack the enzyme system and do not have the metabolic activity of their own.
  • Viruses are not able to survive without a host cell, so active viruses reside inside a host body. They are present either in a bacterial cell, animal cell or plant cell.
  • Size:  Viruses are much smaller than Bacteria. Their Size ranges from 20 – 1400nm.  The poliovirus is 30nm.  Giant Mimi viruses are up to 800 nm.
  • Different shapes of Viruses: Viruses are of different shapes. They are rod-shaped, bullet-shaped, filament shaped, icosahedral in shape and tadpole-shaped.

 

Virus structure
Virus structure

Viral Structure:  Virus consists of nucleic acid and a protein. Genome or the nucleic acid is covered by a protein coat called the capsid.  Some viruses have an envelope outside the capsid.  A virus without the envelope is called the Naked virus.

  • VIRUS Genome: It consists of either deoxyribonucleic acid(DNA) or ribonucleic acid ( RNA).  It may be a single-stranded form or double-stranded, Either circular or linear.
  • Viral Capsid:  Viral nucleic acids surrounded by Protein coat called Capsid. Viral capsid is of 3 types. Helical, Icosahedral  Complex.

 

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