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Flashcards in Roles of Transmembrane Proteins Deck (12):

Why can ions or polar molecules not pass straight through the membrane and how do they overcome this?

Ions and polar molecules are unable to go straight through the membrane due to the hydrophobic centre, and so they must pass through a specific channel or transporter protein.


What do channel proteins do?

Channel proteins allow ions or polar molecules to move from one side of the membrane to the other through passive transport as no energy is needed. Each type of channel protein is specific to the ion/molecule it allows through.


What is a gated channel?

A gated channel protein is one that can change their conformation and either be opened to allow diffusion of their ion or closed to prevent diffusion of their ion. They can either be ligand-gated or voltage-gated.


Describe how a ligand-gated channel works.

Ligand-gated channel proteins allow the passage of solutes by changing conformation when a ligand binds to or detaches from the ligand-binding site of the channel protein.


Describe how a voltage-gated channel works.

Voltage-gated channel proteins allow the passage of solutes by changing conformation when there is a large enough change in the ion concentrations across a membrane.


What is aquaporin?

Aquaporin is a channel protein that lets water molecules through the cell membrane. It has a hydrophilic centre to help the water pass through and is an ungated channel so the water molecules pass through the channel by facilitated diffusion as no conformation change is needed.


What are transporter protiens and what do they do?

Transporter proteins bind to a specific ion or molecule which causes them to change confomation and transport the ions/molecules across the membrane.


What does it mean when a transporter protein operates passively or actively?

- A passive trasporter protein does not require energy as it flows with the concentration gradient. An example is the GLUT4 glucose transporter found in fat and muscle cells. This transporter protein passes glucose across these membranes through facilitated diffusion.
- An active transporter protein requires energy from the hydrolysis of ATP as it goes against the concentraion gradient. An example is the sodium-potassium pump.


What is coupled transport?

- Coupled transport is a passive process where the movement of one material going with its concentration gradient is used to pull another material uphill against its concentration gradient.
- An example of this is the glucose symport process in the lining cells of the small intestine. The flow of sodium ions along their concentration gradient allows glucose molecules to be moved up against their concentration gradient.


When does signal transduction occur and what does it do?

- Signal transduction occurs when an extracellular signal molecule binds to its receptor which causes an intracellular response. The receptor could be on the membrane or inside the cell.
- It can also cause a change in the uptake or secretion of molecules, rearrange the cytoskeleton, or activate proteins involved in regulating gene expression.


Describe the signal transduction pathway.

1) The extracellular signal molecule binds to the receptor which causes a conformatinal change in the receptor protein.
2) The change in conformation triggers a signal transduction pathway in the cell which amplifies the signal through a cascade of G-proteins/enzymes and this causes an intracellular response.


How do G-protiens work in a signal transduction pathway?

G-proteins can transmit signals from the receptor protein to inside the cell. G-proteins can be activated by binding to GTP or deactivated by binding to GDP.