cell communication 2

Question 1

Explain the structure of G-protein-coupled receptors (GPCRs) and describe the types of extracellular signal molecules that bind to them.

Answer 1

• bind to complex of protein called g
• bind to gtp and hydrolyze it to gdp
• once receptor activated, G protein activated and then is first ICM in pathway and can activate the rest
• large family, cross membrane 7 times
• c terminal binds with G proteins
• target of drugs
• types of signals:
  odourants, light, ions, nt (acetylcholine), peptide, lipids, amino acids
• type of receptors: olfactory and light (rhodopsin)

Question 2

Explain the general structure of a G protein and describe how the protein responds when activated by a GPCR.

Answer 2

• G protein activated by recpeort
• GPCRS trimeric: 3 subunits, alpha beta and gamma
• alpha: bind gtp and hydrolyze It
• beta and gamma: part of complex and ICSMS
• alpha and gamma: integeral proteins
• signal binding, change conformation of receptor, leads to change in conformation of alpha subunit, loses affinity or GDP and binds GTP, dissociates complex
• relay has occurred
• alpha subunit with gtp reduced and is active and can stimulate target protein
• 20 diff types of mammalian g proteins, each recperot works with a type and stimulate a type of protein
• G PROTEIN is a molecular switch, alpha subunit, activate when binding gtp, inactive when gtp hydrolyze to gtp
• some g proteins directly regulate ion channels effector protein

slow heartbeat: G protein binds to acetylcholine, g protein acivtated, alpha and betagamma separate, beta gamma complex stimulate K+ channel, K+ outflow out of cell, heartbeat decrease hyperpolarzation leads to slow down of heart –> effector protein is a channel

Question 3

Summarize the factors that determine the duration of a GPCR-stimulated response.

Question 4

Compare the speeds of the responses produced by G proteins activating an ion channel versus activating a membrane-bound enzyme.

Question 5

Name the two enzymes that are the most frequent targets of Gproteins, andlist thesecond messenger molecules they produce.

Answer 5

• adenyl cyclase
• converts anp into cynic anp (second messenger)
• phospholipase c
• breaks down phospholipid in membrane to 2 small ICSM (inositol triphosphate and diacylglycerol)

Question 6

Explain how cyclic AMP is produced in response to G protein activation.

Answer 6

• 2 signal transduction pathways
• one for adenylate cyclase
• CAMP produced, binds and activate kinase, many other proteins acitvated
• one for phospholipase c
• produces other ICSM second messengers
• products of breakdown of phospholipid DAG and IP3
• calcium released via IP3

Question 7

Compare a signaling pathway in which cyclic AMP produces a response within seconds to one in which the response takes minutes or hours to develop.

Question 8

Give the location and action of the second messenger molecules produced by activated phospholipase C.

Question 9

Explain how calcium-responsive proteins such as calmodulin propagate a calcium ion signal.

Question 10

Explain how GPCRs in the photoreceptors of the retina transmit an extremely rapid signal in response to stimulation by light.