Lecture 19: Cell Signaling I

Question 1

What are some examples of Direct Cell Signaling

Answer 1

*Cells are directly touching one another
-Juxtacrine Signaling
-Gap Junctions
Signaling through plasmodesmata

Question 2

What are some examples of paracrine signaling

Answer 2

autocrine signaling
neuron signaling
paracrine (to another cell signaling)

Question 3

What is endocrine signaling

Answer 3

through the blood stream to act on the target organ

Question 4

What are the steps of cellular signaling

Answer 4

1. receptor ligand binding
2. Signal transduction sometimes via second messengers
3. Cellular response
   4 changes in gene expression

Question 5

__________ signaling molecule fits binding site on tis complementary receptor other signals do not fit

Answer 5

specificity

Question 6

_____________ when enzymes activate enzymes, the number of affected molecules increases geometrically in an enzyme cascade

Answer 6

amplification

Question 7

____________ proteins with multivalent affinities form diverse signaling complexes from interchangeable parts. Phosphorylation provides reversible points of interaction

Answer 7

modularity

Question 8

____________ receptor activation triggers a feedback circuit that shits of the receptor or removes its from the cell surface

Answer 8

Desensitization and adaptation

Question 9

____________ when two signals have opposite effects on the metabolic characteristic such as the concentration of a second messenger X or the membrane potential Vm the regulatory outcome results from the intregrated input from both receptors

Answer 9

integration

Question 10

_______ when the enzyme that destroys an intracellular message is clustered with the message producer, the message is degraded before it can diffuse to distant points, so the reponse is only local and brief

Answer 10

localized response

Question 11

________ external ligand (L) binding to receptor (R) activates an intracellular GTP binding receptor protein (G) which regulates an enzyme that generates an intracellular second messenger

Answer 11

G protein coupled receptor

Question 12

_____________________ ligand binding activates tyrosine kinases activity by autophosphorylation

Answer 12

receptor enzyme

Question 13

____________ transcription factor T altering gene expression

Answer 13

kinase activités

Question 14

_____________ channel opens or closes in response to concentration of signal ligand or membrane potential

Answer 14

gated ion channel

Question 15

_____________ hormone binding allows the receptor to regulate the expression of specific genes

Answer 15

nuclear receptor

Question 16

What are some disease associated with G protein receptors

Answer 16

depression, cancer, blindness, diabetes

Question 17

G protein receptors is A plasma membrane receptor with
______________s, an enzyme in the plasma
membrane that generates an
intracellular second messenger, and
a guanosine nucleotide–binding
protein (G protein).

Answer 17

seven transmembrane helical
segment

Question 18

G-protein cycles
between ________________ forms, an
effector enzyme or ion channel in the
plasma membrane that is regulated
by the activated G protein.

Answer 18

active (GTP-bound) and
inactive (GDP-bound)

Question 19

What are the steps of epinephrine signaling

Answer 19

1. epinephrine binds to specific receptor
2. Hormone receptor complex causes the GDP bound to Gsa to be replaced by GTP activating Gas
3. activated Gsa separates from GsBy moves to adenyl cycle and activates it. Many GSA subunits may be activated by one occupied receptor
4. Adenyl cyclase catalyzes the formation of cAMP
5. cAMP activates PKA
6. Phosphorylation of cellular proteins by PKA cause the cellular response to epinephrine
7. cAMP is degraded reversing the activation of PKA

Question 20

Gs proteins are __________ via the GTPase switch. Intrinsic GTPaseactivity hydrolyses GTP spontaneously thereby inactivating the protein

Answer 20

Self activating

Question 21

cAMP as a second messenger activates ____________________

Answer 21

Protein Kinase A

Question 22

________________ brings every major player in the pathway into close proximity, allows pathway to function as an assembly line complex

Answer 22

A kinase anchoring protein

Question 23

______________ is another known component of the complex, yet another way to turn off signaling (PP2A slowly rips off the phosphoryl groups that were installed by PKA)

Answer 23

PP2A Protein phosphatase 2A

Question 24

In terms of terminating GPCR Signaling what are some methods?

Answer 24

1. As epinephrine drops below Kd for its receptors, the hormone dissociated from the receptor and the receptor reassumes it inactive conformation
2. Hydrolysis of GTP bound to G alpha subunit catalyzed the intgrinsic GTPase activity of G protein
3. Remove the second message cAMP is hydrolyzed 5 AMP cyclic nucleotide phosphodiesterase enzyme
4. Activation of phosphoprotein phosphatase which hydrolyze phosphorylated SER, The, Tyr residues releasing inorganic phosphates

Question 25

____________ is a major CA 2+ binding protein in human cells, protein is tropical inactive at low Ca 2+ becomes active at high Ca 2+

Answer 25

Caladium

Question 26

__________ is a cousin of calmodulin preens t in muscle cells that activates tropomyosin

Answer 26

Troponin

Question 27

In rod and cone cells, light actives ___________ which activates G protein transducin

Answer 27

Rhodopsin

Question 28

In the eye: The freed ____________________ of transduction activates a cGMP phosphodiesterase which lowers cGMP and thus closes cGMP dependent ion channels in the outer segment of the neuron

Answer 28

alpha subunit

Question 29

In olfactory neurons, olfactory stimuli, acting through GPCRs and G proteins, _____________________by activating PLC. They affect ion channels and thus membrane potential.

Answer 29

trigger an increase in [cAMP] by activating adenyl cyclase or [Ca2+]

Question 30

________________ have GPCRs that respond to tastants by altering levels of cAMP, which changes the membrane potential by gating ion channels.

Answer 30

Gustatory neurons

Question 31

The bacterial toxin that causes cholera is an enzyme that catalyzes transfer of the ____________________________. The G proteins thus modified fail to respond to normal hormonal stimuli. The pathology of cholera results from defective regulation of adenylyl cyclase and overproduction of cAMP.

Answer 31

ADP-ribose moiety of NAD+ to an Arg residue of Gs

Question 32

The pathway of cholera results form the defective regulation of ___________________

Answer 32

adenyl cyclase and overproduction of cAMP

Question 33

Epinephrine, also called adrenaline, is released from the adrenal gland and regulates energy yielding metabolism in muscle, liver, and adipose tissue. It also serves as a neurotransmitter in __________________ * Its affinity for its receptor is expressed as a dissociation constant for the receptor-ligand complex.

Answer 33

adrenergic neurons.

Question 34

_______________ is an agonist with affinity higher than epinephrine. Used for treatment of acute bradycardia, heart block & shock.

Answer 34

Isoproterenol

Question 35

________________ an antagonist with extremely high affinity. Used for treatment of hypertension, angina, cardiac arrythmia, thyrotoxicosis.

Answer 35

Propanolol