2.3 - Signal Transduction

Question 1

cAMP

Answer 1

activates protein kinase A

Question 2

cGMP

Answer 2

activates protein kinase G and opens cation channels in rod cells

Question 3

DAG

Answer 3

activates protein kinase C

Question 4

IP₃

Answer 4

opens Ca²⁺ channels in the endoplasmic reticulum

Question 5

activation of effector proteins associated with G-protein coupled receptor: process

Answer 5

Question 6

General Structure of G-Protein Coupled Receptor

Answer 6

• 7 transmembrane regions
• 4 extracellular and 4 cytosolic segments

Question 7

switching mechanism of G proteins

Answer 7

conversion of the active form back to the inactive state is mediated by a GTPase, which slowly hydrolyzes the bound GTP to GDP and Pi, thus altering the conformation of the switches so they are unable to bind to the effector protein

Question 8

where is GTPase found?

Answer 8

can be an intrinsic part of the G protein or a separate protein

Question 9

GEF

Answer 9

proteins or protein domains that activate monomeric GTPases by stimulating the release of guanosinediphosphate (GDP) to allow binding of guanosinetriphosphate (GTP).

Question 10

G protein complex stimulatory or inhibitory?

Answer 10

G protein complex can be either

Question 11

G protein fluroescence experiment

Answer 11

• CFP normally fluoresces at 490 nm; YFP at 527 nm
• When CFP and YFP are nearby energy transfers can happen (when Galpha-GBy complex)
• irradiation of resting cells with 440 nm (which excites CFP) light causes emission of 527 nm light, characteristic for YFP
• if ligand binding leads to dissociation of alpha and By subunits then fluorescence energy transfer cannon occur –> irradiation of cells at 440 nm would cause an emission of 490 nm light

Question 12

structure of adenylyl cyclase

Answer 12

• two similar catalytic domains, which convert ATP to cAMP
  
  • cytosolic side
• two integral membrane domains

Question 13

degradation of glycogen

Answer 13

glycogen goes through glycogen phosphorylase ⇒ glycogen + glucose-1-phosphate

Question 14

signal transduction pathway: epinephrine → glucose release

Answer 14

Question 15

regulation of glycogen metabolism by cAMP and PKA: effects of increasing and decreasing cAMP

Answer 15

Question 16

effect of pertussis toxin

Answer 16

impossible to activate the G(alpha) protein; blocks the exchange of GDP to GTP; cannot activate the alpha subunit

Question 17

cholera toxin

Answer 17

disrupts G-protein coupled receptor pathways in the intestine disrupting ion flow; ruins the GTPase activity of the alpha subunit and the GTPase stays on all the time; overstimulates the system causing excessive water loss

Question 18

rehydration therapy

Answer 18

solution given to patients — composed of water, sugar, and salt; way to move water into the intestinal cells

Question 19

ways to inactivate G-protein-linked receptors

Answer 19

• cAMP phosphodiesterase
• inactivation via phosphorylation by PKA (desensitized receptor)
• Beta-arrestins (internalization of receptor)

Question 20

Role of beta-arrestin in GPCR desensitization and signal transduction

Answer 20

• Beta-arrestin binds to phosphorylated serine and threonine residues in the C-terminal segment of G-protein-coupled receptors (GPCRs). Clathrin and AP2, two other proteins bound by Beta-arrestin, promote endocytosis of the receptor.
• Beta-Arrestin also functions in transducing signals from activated receptors by binding to and activating several cytosolic protein kinases
• interaction of Beta-Arrestin with three other proteins results in phosphorylation and activation of another transcription factor

Question 21

rhodopsin composed of:

Answer 21

retinal + opsin

Question 22

retinal

Answer 22

light-absorbing pigment

Question 23

opsin

Answer 23

contains GPCR of rhodopsin

Question 24

where is rhodopsin found?

Answer 24

only in rod cells – in the discs of the outer segment

Question 25

activating signal of rhodopsin

Answer 25

absorption of a photon of light causes transformation of retinal from the Cis form to Trans

Question 26

Effect of Light on Rhodopsin: The Pathway/Process

Answer 26

1. light activates rhodopsin
2. activated rhodopsin binds to inactive G(alpha, t) protein which has GDP
3. GDP gets replaced with GTP
4. G(alpha, t) - GTP binds to inactive PDE y-subunits and activates cGMP phosphodiesterase (PDE)
5. y-subunits dissociate from alpha and beta subunits of PDE
6. alpha and beta subunits of PDE hydrolyze cGMP into GMP
7. cytosolic concentration of cGMP decreases
   as a result, cGMP dissociates from nucleotide gated channel in plasma membrane and channels close
8. membrane becomes hyper polarized –> neurotransmitter release reduced
9. G(alpha, t) - GTP and PDE y subunits bind to GTPase activating complex
10. bound GTP gets hydrolyzed –> inactivation of phosphodiesterase

Question 27

summary: what does activation of rhodopsin with light do?

Answer 27

activation of rhodopsin by light ⇒ closing of cGMP-gated cation channels

Question 28

relaxation of arterial smooth muscle referred to as the ___ pathway

Answer 28

Ca2+ / NO (nitric oxide) / cGMP pathway

Question 29

process of arterial smooth muscle relaxation

Answer 29

Question 30

types of phospholipases encountered

Answer 30

PLC is most common; PLD also appears

Question 31

where does PLC (and PLD) cleave on PIP₂?

Answer 31

PLC: cleaves right before the phosphate

PLD: cleaves right after phosphate

Question 32

where on cell is PLC protion located?

Answer 32

PLC is an integral membrane protein

Question 33

PLC-PKC pathway

Answer 33

Question 34

what does DAG stand for?

Answer 34

diacylglycerol

Question 35

G-proteins typically activate:

Answer 35

adenylyl cyclase or phospholipase C

Question 36

what are the second messengers we get from phospholipase C?

Answer 36

• DAG
• IP₃
• Ca⁺² (from IP₃-gated Ca⁺² channel)