What is Difference Between Active and passive cell transport?
Difference Between Active and passive cell transport is that Active and passive cell transport is the transfer of solutes from one side of the cell membrane to the other. Transportation is passive when a metabolic energy source such as ATP is not required, while transportation is active when using ATP as an energy source.
The cell membranes are mainly composed of a lipid bilayer that hinders the passage of certain types of substances. This barrier function allows the cell to maintain solute concentrations in the cytosol different from the extracellular environment or intracellular compartments.
| Passive transport | Active transport | |
|---|---|---|
| Definition | Transfer of solutes through the lipid membrane without energy. | Transfer of solutes through the lipid membrane associated with an energy source. |
| Concentration gradient | In favor. | Against. |
| Membrane proteins | Channels and conveyors. | Conveyors or pumps. |
| Driving force | Electrochemical gradient. | ATP. |
| Examples | Water transport through aquaporins. | Transport of sodium Na + ions by sodium-potassium ATP-asa. |
What is passive cell transport?
Passive transport is the process that allows the passage of molecules and ions through the cell membrane without a source of energy.
The concentration gradient or concentration difference of a species between the two sides of the membrane is the impulse that determines the movement and direction of passive transport.
When the solute has a charge (positive or negative), the difference in potential between the two sides of the membrane (membrane potential) can also boost transport. In this case, the combined concentration gradient and electrical gradient form the electrochemical gradient conductive force.
By generating a difference in ionic concentrations through the lipid layer, the cell membrane can store potential energy in the form of electrochemical gradients. Electrochemical gradients are used to:
- boost various transport processes,
- transmit electrical signals in electrically excitable cells and
- produce the majority of ATP in mitochondria, chloroplast, and bacteria.
Passive transport characteristics
- The movement of solutes follows the concentration gradient, from higher concentration to lower concentration.
- It depends on the concentration gradient, particle size, and temperature.
- Ions and small molecules are mobilized.
- It does not require hydrolysis of ATP.
- It is mediated by transmembrane proteins, channels, and transporters, in facilitated diffusion.
Types of passive transport
The molecules and ions can pass through the membrane passively through different mechanisms: simple diffusion facilitated diffusion or osmosis.
SIMPLE BROADCAST
Small non-polar molecules such as oxygen O 2 and carbon dioxide CO 2 dissolve easily in the lipid membranes. Small polar molecules without charge, such as H 2 O water and urea, also diffuse through the membrane in a slow or restricted manner. In general, lipophilic or fat-related molecules can cross the membrane by simple diffusion.
DIFFUSION FACILITATED
The cells developed mechanisms for transferring water-soluble molecules and ions across the membrane. Ions and molecules are transported through specialized transmembrane proteins (cross the membrane). As the diffusion of greater concentration occurs at a lower concentration with the help of “passageways”, there is the talk of facilitated diffusion. Thus:
- essential nutrients enter the cell;
- eliminate metabolic waste products, and
- regulate intracellular ion concentrations.
The two main classes of membrane proteins that facilitate the traffic of molecules in and out through the lipid membrane are:
- the transporters: they are proteins that have movable parts, like doors of the membrane that open and close letting the solute pass. They are like revolving doors in the membrane.
- the channels: they form narrow hydrophilic pores that allow passive movement, mainly of small inorganic ions. Although water can diffuse through lipid membranes, all cells contain protein channels called aquaporins that increase the permeability of these membranes to water.
OSMOSIS
Osmosis is the movement of water through a semipermeable membrane when on one side there is a solute that cannot cross the membrane. In osmosis, only water movement occurs.
What is active cell transport?
Active transport is the process by which the cell transports material against its concentration gradient, using ATP as its energy source.
Characteristics of active transport
- It is done through integral membrane proteins.
- It is specific to the solute.
- It experiences saturation, that is, when all solute binding sites are occupied, no matter how much more substrate is added, the flow remains constant.
Types of active transport proteins
At least three types of proteins with the ability to perform active transport are described in the cells. Below its description.
Lysosome enzymes work at pH around 5 and the lysosome maintains that pH by the proton pump.
The ATP pumps transport the solute coupled to the ATP hydrolysis, that is, the ATP releases a phosphate group (PO 4 -3 ) and transforms into ADP. The energy released in hydrolysis is what “pumps” the solute from one side of the membrane to the other.
Active transport driven by hydrolysis of ATP is also known as primary active transport.
There are three types of ATP pumps:
- P-type pumps: the protein phosphorylates (a phosphate group is attached to the protein) in the transport process. Examples: sodium-potassium pumps, calcium pumps.
- Type-F pumps: also called ATP synthetases because they use the proton gradient to synthesize ATP from ADP and phosphate. Examples: the chloroplast ATP synthetase associated with the light-dependent phase of photosynthesis.
- ABC transporters: these are membrane proteins that carry small molecules. Examples: the ABCG1 cholesterol transporter, the MDR transporter (multi-drug resistance).
DOCKED CONVEYORS
The transport of an ion or molecule is concomitant with another solute. In this case, the solute in greater concentration on one side of the membrane passes to the other side and promotes the movement of the solute from lower to a higher concentration. Conveyors driven by ionic gradients are also called secondary active transport.
It is carried out by transporter proteins known as sympathizers and anti-carriers. A simportador or cotransportador transports a solute following its concentration gradient in the same direction as another solute against the concentration gradient.
For example, the sodium-dependent glucose cotransporter of the small intestine. In this case, glucose and sodium from inside the intestine are absorbed into the intestinal cell.
Epithelial cells of the intestine or kidney have a large number of sympathizers that are driven by the Na + sodium ion gradient, being more concentrated outside the cell.
In bacteria, the transport of lactose is coupled to the transport of hydrogen ions H +.
An anti-carrier or exchanger transfers solutes in opposite directions. For example, the sodium / proton Na + / H + antiporter enters sodium into the cell and proton exits outside.
LIGHT ACTIVATED PUMPS
Predominant in bacteria and archaea, this solute transport is carried out from lower to higher concentration thanks to the collection of light energy. For example, bacteriorhodopsins and halorhodopsins are proton pumps activated by light.
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