Transmembrane transport

What is cellular homeostasis?

Self-regulating process by which cell maintains a stable environment despite external changes

What is the structure for a channel protein?

Polypeptide which crosses the membrane multiple times

Forms a hollow tube protected from hydrophobic lipids

Selectivity dependent on amino acids lining

What channel facilitates water movement?

Aquaporins

What are the types of ion channels?

Leakage channel

Voltage-gated channel

Ligand-gated channel

Signal-gated channel

What is meant by uniporters, symporters and antiporters?

Uniporters transport one substance one way

Symporters transport two substances the same way

Antiporters transport two substances in opposite directions

Give an example of coupled transport, and its mechanism?

Sodium-glucose transport

Sodium binds to protein increasing glucose affinity

Glucose binds causing conformational change, closing outside and opening inside

Sodium then moves into the cell via diffusion and decreases glucose affinity

Glucose is then released which causes the protein to undergo conformational change

What are the types of ATP driven transporters?

P-class

V/F-class

ABC-class

How do P-class transporters work?

Protein is phosphorylated

Ex: Sodium-potassium pump

Transports 3 sodium out and 2 potassium in via phosphorylation (conformational change)

How do V/F-class transporters work?

V-class acidify organelles, ATP hydrolysis causes rotational conformational change and proton release

F-class is for ATP synthesis, proton gradient drives rotation

How do ABC transporters function?

Pumps out small molecules

ATP binding causes conformational change, closes to cytoplasm and opens extracellularly and molecule has reduced affinity so is lost

ATP is hydrolysed and protein changes again