Membrane Proteins Flashcards
What does the phospholipid bilayer act as to ions and most uncharged polar molecules? Why is this?
barrier due to its hydrophobic interactions
What do transmembrane proteins do?
act as channels or transporters controlling the concentration of ions and other molecules within the cell
To perform specialised functions, what do different cell types and different cell compartments have?
different channel and transporter proteins
What kind of process is the passage of molecules through channel proteins?
passive
Water can pass across the plasma membrane by diffusing through the phospholipid bilayer or through water channels. What are these water channels called?
aquaporins
What can some channel proteins be and what does this mean?
gated and change conformation to allow or prevent diffusion
What are the 2 types of gated channels?
ligand gated channels
voltage gated channels
What do gated channels respond to?
a stimulus which causes them to open or close
Describe the difference between a ligand gated channel and a voltage gated channel
Ligand gated channels respond to a chemical stimulus e.g. neurotransmitter. Voltage gated channels respond to the relative concentration of ions
State the function of transporter proteins?
change conformation to transport molecules across a membrane
What two mechanisms do transported proteins work by?
Facilitated transport
Active Transport
Give an example of facilitated transport
glycose symport
Give an example of active transport
sodium-potassium pump
What kind of process is facilitated transport?
passive
What does the sodium-potassium pump do?
Transports sodium out of cells, and potassium ions in
What is the sodium-potassium pump driven by?
the hydrolysis of ATP
What are the key features of the sodium-potassium pump?
- it is a transmembrane carrier (transporter) protein
- it has 3 binding sites for Na+ ions
- it has 2 binding sites for K+ ions
- there is a phosphorylation site to accept Pi from ATP
- two different conformations of the protein are possible (controlled by the phosphorylation state).
Describe the 6 stages that take place during the sodium-potassium pump.
- The pump is open to the cytosol. Na+ ions bind to Na+ binding sites on the pump.
- Na+ binding stimulates the ATPase function that phosphorylates the protein.
- Phosphorylation causes the protein to change conformation. This makes the protein open to the extracellular environment. The Na+ binding site now have lowered affinity for Na+, so they are released.
- The K+ binding sites have a high affinity for K+, so they are occupied . This triggers the release of the phosphate group.
- Loss of the phosphate group causes a conformational change so the pump is open to the cytosol once again. K+ binding sites have a lower affinity for K+, so K+ ions are released. Cycle repeats
