Question

Explain substrate transfer through cell membrane

Answer 1

ans:)The diffrent types of substrate transfer through the cell membrane are

Cellular membranes possess two qualities:

• They are semi-permeable (only certain materials may freely cross – large and charged substances are typically blocked)
• They are selective (membrane proteins may regulate the passage of material that cannot freely cross)

* Facilitated transport:Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.

Facilitated transport is a type of passive transport. Unlike simple diffusion where materials pass through a membrane without the help of proteins, in facilitated transport, also called facilitated diffusion, materials diffuse across the plasma membrane with the help of membrane proteins

A concentration gradient exists that would allow these materials to diffuse into the cell without expending cellular energy. However, these materials are ions or polar molecules that are repelled by the hydrophobic parts of the cell membrane. Facilitated transport proteins shield these materials from the repulsive force of the membrane, allowing them to diffuse into the cell.

The material being transported is first attached to protein or glycoprotein receptors on the exterior surface of the plasma membrane. This allows the material that is needed by the cell to be removed from the extracellular fluid. The substances are then passed to specific integral proteins that facilitate their passage.

Some of these integral proteins are collections of beta-pleated sheets that form a channel through the phospholipid bilayer. Others are carrier proteins which bind with the substance and aid its diffusion through the membrane.

* Active Transport:The sodium-potassium pump maintains the electrochemical gradient of living cells by moving sodium in and potassium out of the cell.

The primary active transport that functions with the active transport of sodium and potassium allows secondary active transport to occur. The secondary transport method is still considered active because it depends on the use of energy as does primary transport.

One of the most important pumps in animals cells is the sodium-potassium pump ( Na⁺-K⁺ ATPase ), which maintains the electrochemical gradient (and the correct concentrations of Na⁺ and K⁺) in living cells. The sodium-potassium pump moves two K⁺ into the cell while moving three Na⁺ out of the cell. The Na+-K+ ATPase exists in two forms, depending on its orientation to the interior or exterior of the cell and its affinity for either sodium or potassium ions.

passive transport

Passive transport involves the movement of material along a concentration gradient (high concentration to low concentration)Because materials are moving down a concentration gradient, it does not require the expenditure of energy (ATP hydrolysis) this are of three types:

OsmosisOsmosis is the movement of water across a membrane from an area of low solute concentration to an area of high solute concentration.

Osmosis is the movement of water through a semipermeable membrane according to the concentration gradient of water across the membrane, which is inversely proportional to the concentration of solutes.

Semipermeable membranes, also termed selectively permeable membranes or partially permeable membranes, allow certain molecules or ions to pass through by diffusion

While diffusion transports materials across membranes and within cells, osmosis transports only water across a membrane. The semipermeable membrane limits the diffusion of solutes in the water.

*simple Diffusion:Diffusion is a passive process of transport.

A single substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across a space.

We are familiar with diffusion of substances through the air. For example, think about someone opening a bottle of ammonia in a room filled with people. The ammonia gas is at its highest concentration in the bottle; its lowest concentration is at the edges of the room.

The ammonia vapor will diffuse, or spread away, from the bottle; gradually, more and more people will smell the ammonia as it spreads. Materials move within the cell ‘s cytosol by diffusion, and certain materials move through the plasma membrane by diffusion.

Diffusion expends no energy. On the contrary, concentration gradients are a form of potential energy, dissipated as the gradient is eliminated.

Each separate substance in a medium, such as the extracellular fluid, has its own concentration gradient independent of the concentration gradients of other materials.

In addition, each substance will diffuse according to that gradient. Within a system, there will be different rates of diffusion of the different substances in the medium.

Facilited diffusion: Facilitated diffusion is the passive movement of molecules across the cell membrane via the membrane protein.

It is utilised by molecules that are unable to freely cross the phospholipid bilayer (e.g. large, polar molecules and ions)

This process is mediated by two distinct types of transport proteins – channel proteins and carrier proteins