Cell Signaling

Question 1

Types of intercellular signals

Answer 1

Endocrine, paracrine, autocrine, neuronal, and contact

Question 2

Endocrine

Answer 2

Cell sends signal into the blood stream to act on something that is far away (hormones, insulin, epinephrine, etc…)

Question 3

Autocrine

Answer 3

Act on the same cell that makes them (growth factors and eicosanoids)

Question 4

Paracrine

Answer 4

Acts on adjacent/nearby cells (neurotransmitters, growth factors, nitric oxide)

Question 5

Neuronal Signaling

Answer 5

Synaptic signaling with neurotransmitters

Question 6

Contact signaling

Answer 6

Signaling between cells that are in direct contact

Question 7

Specificity

Answer 7

In regards to intercellular systems, a signal molecule is highly specific for its own receptor

Question 8

Amplification

Answer 8

When enzymes activate other enzymes there is an enzyme cascade

Question 9

Desensitization/activation

Answer 9

Receptor activation triggers a feedback circuit that shuts off the receptor or removes it from the cell surface

Question 10

Integration

Answer 10

When two signals have opposite effects on a metabolic characteristic the outcome is integrated output from both. (E.g., if one increase the concentration and another decrease it, the response will be a mixture of the two)

Question 11

What is the only intracellular receptor that is not on the surface of the cell?

Answer 11

steroid receptor which is in the nucleus, allowing it to roulade the expression of specific genes.

Question 12

What is the general mechanism for hormone molecules?

Answer 12

They are hydrophobic (lipophilc) and work by inducing gene expression at the level of DNA transcription.

Question 13

Gated Ion Channel

Answer 13

Receptor linked to ligand or voltage-gated ion channel. Binding of neurotransmitter will make the channel open, resulting in ions moving through the channel.

Question 14

What are some examples of gated ion channels?

Answer 14

Nicotinic ACh receptors in the muscles and nerve or GABA and glycine in the CNS

Question 15

Receptor Enzyme (catalytic receptor)

Answer 15

Extra cellular receptor with intracellular tyrosine kinase activity.

Question 16

Insulin Receptor

Answer 16

Insulin receptor is a tyrosine kinase enzyme in which the binding of a ligand leads to ATP cleavage and the activation of the tyrosine kinase. This can lead to the stimulation of GLUT-4, stimulation of protein synthesis, and induction/repression of genes.

Question 17

Examples of second messengers

Answer 17

cAMO, IP3, DAG, Ca, cGMP, NO

Question 18

If the stimuli is epinephrine/norepinephrine, what is the system?

Answer 18

Epi is received by B-adrenergic receptor which activates the adenylate cyclase system

Question 19

What are the steps in the adenylate cyclase system?

Answer 19

1) Molecule binds
2) GDP on Gs (alpha) is replaced by GTP activating it
3) complex splits up and Gsalpha moves over and activates adenylate cyclase
4) adenylate cycle forms cAMP
5) cAMP activates PKA (enzyme)
6) PKA phosphorylase proteins leading to response
7) cAMP is degraded

Question 20

Why is the action of the G-protein short lived?

Answer 20

There is an inborn GTPase activity that hydrolysis GTP back to GDP turning off the system. Can self regulate.

Question 21

What terminates the effect of cAMP?

Answer 21

Phosphodiesterase hydrolysis cAMP to AMP

Question 22

What will inhibit phosphodiesterase?

Answer 22

Caffeine and theophylline

Question 23

What inactivates GTP-ase activity?

Answer 23

ADP ribosylation of the G alpha

Question 24

How does cholera and E.coli work?

Answer 24

They both ADP-ribosylate Gs-alpha resulting in continuously active Gs-alpha

Question 25

How foes the pertussis toxin work?

Answer 25

ADP ribosylates Gi-alpha resulting in a continuously inactive Gi-alpha

Question 26

Phosphoinositide System

Answer 26

1) Gqa activates phospholipase C
2) PLS leaves PIP2 into IP3 and DAG
3) IP3 causes Ca to be released from the ER
4) DAG activates membrane bound protein kinase C
5) Protein Kinase C pohosphrylates proteins resulting in cellular responses

Question 27

What does protein kinase C need for maximal activity?

Answer 27

DAG, Calcium, and phospholipids

Question 28

CGMP

Answer 28

Acts as a specialized messenger in smooth muscle relaxation, platelet aggregation, and the visual system. Not associated with G-proteins

Question 29

Nitric Oxide

Answer 29

Synthesized in endothelial cells and diffused to vascular smooth muscle where it activates cytosolic guanylate cyclase which causes smooth muscle relaxation. Considered a vasodilator

Question 30

What second messengers are involved in vasodilation?

Answer 30

IP3, Ca, NO, cGMP