Cell Communication 1: Signal Transduction

Question 1

What is signal transduction?

Answer 1

extracellular signaling molecules bind to specific receptors in target cells to initiate a chain of events

Question 2

Why is signal transduction important?

Answer 2

cell, tissues, and organs need to communicate in the development of the organism and for coordination of metabolism

Question 3

What responses do external signals induce?

Answer 3

fast response

slow response

Question 4

What is fast response?

Answer 4

change in activity or function of enzymes or proteins in the cell

Question 5

What is slow response?

Answer 5

change in amounts of proteins by change in expression of genes

Question 6

What is endocrine signaling?

Answer 6

long distance signaling
signal-bloodstream-distant target cells
freely diffusible signal

Question 7

What is paracrine signaling?

Answer 7

acts locally

affects cells nearby and short lived signal

Question 8

What is synaptic signaling?

Answer 8

acts locally
affects cell nearby
short lived signal
(neurotransmitters)

Question 9

What is autocrine signaling?

Answer 9

cells resign to signals they themselves relates or release to cells of the same type
cells secrete signal that feeds back and binds to a receptor on its own surface

Question 10

What is direct cell signaling?

Answer 10

ex) immune cells

Ag-presenting cells to T cells

Question 11

What do cells do after receiving a signal?

Answer 11

survive
divide
differentiate
die

Question 12

What are the three parts of a signaling module?

Answer 12

signals
receptors
effectors

Question 13

What are signals?

Answer 13

(ligands)
Typically secreted by exocytosis
signals stay near or far

Question 14

what are receptors?

Answer 14

bind specifically to signal molecules with high affinity (signals are produced in low levels)

Question 15

What are effectors?

Answer 15

targets of receptors inside cells: alter activity of many different proteins and generate 2nd messengers (small diffusible molecules like cAMP and Ca2+)

Question 16

What are the main categories of ligands?

Answer 16

small lipophilic molecules: steroid hormones

water soluble molecules - hydrophilic- e.g. growth factors

Question 17

Receptors can bind to ligands with _____ affinity, which means ____

Answer 17

high; great specificity to the ligand (conc of ligand is low in bloodstream)

Question 18

What are the two types of receptors?

Answer 18

cell surface receptors

intracellular receptors

Question 19

What are cell surface receptors?

Answer 19

external domain binds ligand, transmembrane domain anchors receptor, cytoplasmic domain initiates signal by change in conformation

Question 20

What are intracellular receptors?

Answer 20

steroid receptor can have receptor in cytosol- alters gene expression in nucleus

Question 21

Most signaling molecules are hydrophilic and require ______

Answer 21

cell surface receptors

Question 22

One major class of surface receptors that mediate transduce a binding event on the cell surface to send signal inside the cell

Answer 22

G protein coupled receptors

Question 23

What is a G protein coupled receptors?

Answer 23

receptor composed of 3 parts:
extracellular domain
transmembrane domain
cytoplasmic domain

Question 24

What does the extracellular domain do?

Answer 24

binds to ligand

Question 25

What does the transmembrane domain do?

Answer 25

anchors receptor

Question 26

What does the cytoplasmic domain do?

Answer 26

associates with G protein

Question 27

What are the three protein subunits of G proteins

Answer 27

alpha, beta, gamma

Question 28

What are the 3 components of G protein coupled receptor pathways?

Answer 28

inactive receptor receptor G protein inactive effector

Question 29

G protein coupled receptors are characterized by _______

Answer 29

seven membrane spanning alpha helices

Question 30

What type of proteins are G proteins? what do they assist in?

Answer 30

guanine nucleotide binding proteins | assit in transmitting signals to intracellular targets

Question 31

What is an example of an effector?

Answer 31

downstream adenylyl cyclase that generate cAMP

Question 32

What are the steps of G-protein relaying signals?

Answer 32

1. ligand binds to receptor 2. conformational change occurs in receptor 3. receptor binds to G protein 4. receptors acts as guanidine exchange factor 5. confirmation of G alpha protein is changed to kick out GDP for GTP 6. G alpha becomes active and binds effector molecule to activate it 7. effector molecule can catalyze formation of cAMP

Question 33

What is the target in the cholera toxin?

Answer 33

G protein

Question 34

What does cholera do to G protein?

Answer 34

modifies it by keeping the G alpha in the GTP active form indefinitely, pathway is always active causing Cl- and water to pump out of cells in intestines to cause severe diarrhea

Question 35

G alpha s stimulates ________

Answer 35

adenyly cyclase

Question 36

G alpha I inhibits _______

Answer 36

adenyly cyclase

Question 37

cAMP interacts with target proteins to cause a _______ and activates a protein kinase called ______

Answer 37

biological response; PKA

Question 38

What does a kinase do?

Answer 38

phosphorylates proteins to either activate or inactivate them

Question 39

________ induces activation of PKA

Answer 39

epinephrine

Question 40

What does the downstream do?

Answer 40

generate lots of ATP for a response to threat in liver: glycogen breakdown to glucose, inhibition of glycogen synthesis cardiac muscles: increase contraction rate adipose tissue: hydrolysis of triglycerides to generate more glucose

Question 41

What is desensitization?

Answer 41

ability to turn off or reject the signal

Question 42

What ways can desensitization occur?

Answer 42

receptor sequestration receptor destruction hormone level drop remove the signaling molecule

Question 43

What is receptor sequestration?

Answer 43

endoscope- invagination of membrane

Question 44

What is receptor destruction?

Answer 44

endoscopes and lysosomes

Question 45

What is hormone level drop?

Answer 45

decreased adenyly cyclase activity to decreased cAMP and decreased PKA activity

Question 46

What is removing the signal molecule?

Answer 46

phosphodiesterase will remove cAMP

Question 47

What do G protein receptor kinases do?

Answer 47

phosphorylate the receptor such that another protein called arresting will bind to the 3rd intracellular loop of receptor and prevent G alpha from interacting with third loop of the receptor

Question 48

What does GRK result in?

Answer 48

G protein G alpha-GDP does not get converted to G alpha-GTP by receptor