Kandpal - Signal Transduction and Gene Expression

Question 1

what are 2 types of signals

Answer 1

1. to environment = pheromones (sex pheromones)

2. signal for other cells in same organism = hormones, morphogens, and neurotransmitters

Question 2

what are 4 ways a signal is transmitted

Answer 2

contact-dependent, paracrine, synaptic, and endocrine

Question 3

what is contact-dependent signaling and when is it used

Answer 3

signal is sent forward or backward physically touching other cell - in development and immune response

Question 4

what is paracrine signaling and when is it used

Answer 4

uses a local mediator - signals neighboring cells

Question 5

what is synaptic signaling and when is it used

Answer 5

signaling a specific target (one signal can affect multiple targets) - neurotransmitter

Question 6

what is endocrine signaling and when is it used

Answer 6

hormone goes into blood stream to signal a whole organism - goes to every cell with that receptor (different types of signals but only specific receptors)

Question 7

what is autocrine signaling

Answer 7

signals secreted by cell can bind to itself to reinforce developmental decisions (differentiation) - community of cells

Question 8

in what situation is autocrine signaling more effective

Answer 8

if neighboring cells follow the same development and all respond to same signal (many tumor cells use autocrine)

Question 9

what is combinatorial signaling

Answer 9

a large number of receptors are expressed in a specific cell at a specific time - the receptor determines the behavior (survive, divide, or differentiate) if signal is gone = apoptosis

Question 10

what type of signals can pass readily through the plasma membrane

Answer 10

hydrophobic signals

Question 11

what do hydrophilic signals need in order to go through the plasma membrane

Answer 11

ligands need to bind to receptors on cell surface and transduce an effect

Question 12

how is nitric oxide NO made

Answer 12

arginine + NADPH -> (nitric oxide synthase) -> citrulline + nitric oxide + NADP+

Question 13

what is the response when acetylcholine is released by autonomic nerves in the walls of blood vessels

Answer 13

smooth muscle relaxation

Question 14

what mediates acetylcholine

Answer 14

activation of NO synthase which produces NO inside endothelial cells

Question 15

what does NO bind to after crossing membrane into smooth muscle cells

Answer 15

guanylyl cyclase

Question 16

how is cGMP activated to mediate a rapid relaxation of smooth muscle cells

Answer 16

after NO is bound to guanylyl cyclase -> GTP -> cGMP

Question 17

what is the target protein for protein kinase G (PKG)

Answer 17

phospholipase C-beta dependent IP3 (insoitol triphosphate)

Question 18

how is PKG activated and what is the effect/response

Answer 18

Protein kinase G (PKG) is inactive until cGMP binds to R site and is phosphorylated at the C site = active PKG
response = PKG can phosphorylate a protein

Question 19

what does viagra inhibit in the NO signaling pathway

Answer 19

it inhibits phosphodiesterase (PDE5) so Ca2+ levels decrease from accumulation of cyclic nucleotides and cause sustained relaxation of smooth muscle cells allowing blood vessels to expand

Question 20

what are 2 possible ways nitroglycerine enter the NO signaling pathway

Answer 20

1. nitroglycerine is being converted to NO and then binding to guanylyl cyclase
2. nitroglycerine is directly modifying the reaction is some way (mechanisms are still unknown)

Question 21

what do phosphodiesterases (PDE) do

Answer 21

convert cyclic nucleotides (ex. cGMP or cAMP) into nucleotide monophosphates by hydrolyzing them

Question 22

what happens if phosphodiesterases (PDE) are inhibited

Answer 22

accumulation of cyclic nucleotides (that are not hydrolyzed) -> lower Ca2+ levels -> sustained relaxation of smooth muscle cells (instead of rapid)

Question 23

what are 3 types of phosphodiestereases and where are the expressed

Answer 23

PDE3- cardiac cells
PDE5 - expandable erectile tissue
PDE6- retina

Question 24

what are some examples of hydrophobic signals

Answer 24

cortisol, estradiol, thyroxine, testosterone, vitamin D, retinoic acid

Question 25

what do all the hormone receptors belong to and have in common

Answer 25

nuclear receptor superfamily - all have DNA binding domain = ability to modulate transcription

Question 26

what is a primary (early) response to steroid hormones

Answer 26

induction of transcription in nucleus (steroid hormone + steroid hormone receptor = binds to receptor-steroid-hormone complex)

Question 27

what is a secondary (delayed) response to steroid hormones

Answer 27

primary response activates secondary-response genes to transcribe for proteins other than the target protein

Question 28

what is HSP90

Answer 28

an inhibitor - it binds to ligand-domain until ligand comes in and it dissociates