Cell Signaling II

Question 1

Which neurotransmitter is in control of CNS in a person sound asleep?

Answer 1

GABA

Question 2

What does glutamate do?

Answer 2

Excitatory - opens Na, Ca channels, upregulated in CNS

Question 3

What are the four main second messengers?

Answer 3

cAMP/cGMP, Ca2+, Inositol triphosphate (ITP), Diacyl glycerol (DAG)

Question 4

What is the major inhibitory neurotransmitter in the CNS?

Answer 4

GABA

Question 5

Describe the Gs pathway of protein kinase A (PKA).

Answer 5

1) Epinephrine binds to β2 receptor.
2) Dissociation of Gαs from Gβ and activation of Gαs with GTP - ENZYMATIC
3) Gαs-GTP binds to adenylyl cyclase
4) Adenylyl cyclase makes cAMP – ENZYMATIC
5) cAMP binds and activates PKA
6) PKA adds phosphate to target proteins - ENZYMATIC

Question 6

What is the general name for enzymes that phosphorylate? For enzymes that dephosphorylate?

Answer 6

Protein kinase

Protein phosphatase

Question 7

What amino acids to kinases target for phosphorylation?

Answer 7

Serine, Threonine, Tyrosine (Have OH groups)

Question 8

β 2 agonists like albuterol are bronchodilators. Albuterol binds to β 2 receptors on the smooth muscle in the lungs and results in dilation of airway.

Is formation of cAMP from ATP in the signaling pathway enzymatic (involves signal amplification) or stoichiometric (no signal amplification)?

Answer 8

Enzymatic

Question 9

Describe the GPCR-dependent mechanism of activation of Protein Kinase C (PKC).

Answer 9

1) Signal binds GPCR
2) GDP on GPCR replaced with GTP, activating GPCR
3) GTP-bound subunit (Gq) activates Phospholipase C
4) Phospholipase C activates IP3 and DAG
5) IP3 binds Ca2+ channel on inside of cell
6) Ca2+ enters cell from endoplasmic reticulum
7) Ca2+ and DAG bind PKC and activate it

Question 10

Describe the three subunits of a G protein in a resting, inactive, and activated state.

Answer 10

Resting State - α subunit bound to β γ subunits

Inactive State - GDP-bound G protein with all subunits bound

Activated State - GTP-bound α subunit and dissociated β γ subunit (also activated)

Question 11

How is heart rate regulated?

Answer 11

Signaling through GPCRs that target sinoatrial (SA) node, the pacemaker of the heart

Question 12

What is the signaling pathway to decrease heart rate?

Answer 12

1) Parasympathetic nervous system releases Ach
2) ACh binds M2 receptors and GαI
3) Gβγ subunit opens K+ channels
4) GαI decreases cAMP levels
5) Ca2+ channels close
6) Heart rate decreases

Question 13

What is the signaling pathway to increase heart rate?

Answer 13

1) Sympathetic nervous system releases epinephrine or norepinephrine
2) Epi/Norepi binds β1 receptors and GαS
3) Gβγ subunit increases cAMP levels
4) PKA opens Ca2+ channels
5) K+ channels close
6) Heart rate/contractility increases

Question 14

Describe allosteric control of adenylate cyclase (AC) and its function.

Answer 14

Binding of Gαs increases adenylate cyclase levels.

Binding of GαI decreases adenylate cyclase levels.

AC converts ATP to cAMP

Question 15

Where is smooth muscle in our body?

Answer 15

GI tract: bladder, uterus, penis

Also around blood vessels, air way, glands

Question 16

Explain G protein-coupled signaling in smooth muscle contraction.

Answer 16

Epinephrine binds α1 receptors –> activates Gq –> increases PLC –> increases IP3 –> increases Ca2+ –> CaM kinase increases MLCK activity –> increases myosin-P –> blood vessels and smooth muscle constrict

Epinephrine binds β2 receptors –> activates Gs –> increases AC –> increases cAMP –> increases PKA –> increases MLCP –> decreases myosin-P –> blood vessels and smooth muscle dilate/relax

Question 17

Albuterol (modified epinephrine) is a drug commonly used to treat asthma. What would be the correct signaling cascade that corresponds to albuterol relaxing bronchial smooth muscle resulting in dilation of airway?

Answer 17

Increase GαS –> increase AC –> increase cAMP –> increase PKA –> increase MLCP –> decrease myosin-P

Question 18

Describe how signaling by nitric oxide leads to dilation of coronary arteries, increasing blood flow to heart muscle.

Answer 18

Nitroglycerin –> Nitric oxide increases –> guanylyl cyclase increases –> cGMP increases –> PKG increases –> MLC phosphatase increases –> myosin-P decreases –> relaxation of heart muscle

Question 19

T or F. It’s safe for men on nitrates to take viagra.

Answer 19

False! This could lead to unsafe drop in blood pressure.

Question 20

Describe mechanisms of Viagra in terms of going from a flaccid penis to an erect penis.

Answer 20

Flaccid penis is result of low cGMP and low venous BP due to open veins.

Erect penis is result of high cGMP levels, leading to veins closing and arteries dilating, creatig high arterial BP.

Normally nitric oxide causes high levels of cGMP. Phosphodiesterase converts cGMP to GMP to restore balance. Viagra inhibits PDE5, causing more/longer erections.

Question 21

How is signaling terminated for epinephrine?

Answer 21

1) Methylation by enzyme COMT (in liver and blood)
2) Oxidaiton by enzyme MAO (monoamine oxidase)

Question 22

How is signaling terminated on G proteins?

Answer 22

They have intrinsic GTPase activity and thus inactivate themselves.

GAP (GTPase activating protein) accelerates hydrolysis/inactivation.

Question 23

How is signaling terminated by cAMP and cGMP?

Answer 23

Phosphodiesterases cleave them to AMP, GMP

Question 24

How is IP3-dependent Ca2+ signaling terminated?

Answer 24

1) IP3 is dephosphorylated to IP2 (inactive form) by spcific phosphatase.
2) IP3 phosphorylated to form IP4 (inactive form)
3) Ca2+ pumped out of the cytosol ATP-dependent pumps

Question 25

How is cytoplasmic calcium removed from cytoplasm? (5 ways)

Answer 25

1) By Na/Ca exchanger
2) Pumped out of cells by Ca pump
3) Pumped into sarcoplasmic reticulum by Ca pump
4) Binding to cytoplasmic Ca binding proteins
5) Sequester Ca in mitochondria

Question 26

What happens to all of the phosphorylated proteins in the cell?

Answer 26

Phosphatases remove phosphates from the proteins constantly - they rule the cells and establish the resting state when kinases are inactive.

Question 27

Under pathological conditions, will there be a higher or lower level of phosphatase enzymes in blood?

Answer 27

Higher

Question 28

How is autonomic control of blood supply regulated with epinephrine? How is blood flow changed during emergencies (fight or flight)

Answer 28

By the ratio of α1 and β2 receptors on smooth muscle:

α1, Gq, Ca2+ –> vasoconstriction

β2, Gs, cAMP –> vasodilation

Flow increases to heart, lungs, skeletal muscle

Flow stays the same for the brain

Flow decreases to GI, genitals, skin

Question 29

How does effect of cAMP change in different cell types?

Answer 29

cAMP increases contraction of cardiac muscle, but relaxes smooth muscle

Question 30

What is the heart’s intrinsic heart rate when beating on its own without influence out outside signaling?

Answer 30

100 BPM