Ion Channels, receptor tyrosine kinases

Question 1

for excitable cells, what is depolarization and repolarization? How are ion channels involved?

Answer 1

• depolarization is the when the membrane potential across the cell relative to the resting membrane potential by opening voltage gated positive ions (Na+ and Ca+)
• re polarization pumping K+ out
• ion channels are what pump the ions in and out

Question 2

what is the refractory period and what is it caused by?

Answer 2

• time following an action potential
• period of the inactivation of the Na+ channel

Question 3

why are refractory periods important for conduction of an action potential down a cell like a neuron

Answer 3

• ensures directionality of the movement
• prevent overlapping action potentials
• allow the cell to return to resting state

Question 4

what are 4 general steps of Receptor Tyrosine Kinase activation?

Answer 4

1. ligand binds to receptor monomers causing dimerization
2. juxtaposition of monomers causes cross-phosphorylation of protein kinase domains
3. secondary phosphorylation
4. Proteins bind to phosphorylated sites –> signaling pathways

Question 5

what does an SH2 domain bind to and what do SH3 domains bing to?

Answer 5

• SH2 binds to phosphorylated tyrosines
• SH3 binds to proline-rich sequence
• (involved in regulating receptor tyrosine kinase)

Question 6

what is the MAPK cascade (very simply)

Answer 6

• You don’t need to know names of specific proteins, just that a MAPKKK phosphorylates a MAPKK which then phosphorylates a MAPK, which then phosphorylates downstream targets.