Chapter 16

Question 1

Define mitogen

Answer 1

Extracellular signal that leads to cell division

Question 2

Which types of molecules can directly activate intracellular receptors?

Answer 2

Small and hydrophobic

Question 3

Define endocrine signaling

Answer 3

Extracellular signals that are broadcast throughout the body via the bloodstream

Question 4

Define paracrine signaling

Answer 4

Signal molecules diffuse locally through the extracellular fluid and remain near the cell that secreted them

Question 5

Define autocrine signaling

Answer 5

Cells respond to local mediators that they produced (subcatagory of paracrine)

Question 6

Define neuronal/synaptic signaling

Answer 6

Nerve cells deliver messages over long distances quickly and specifically

Question 7

Define contact dependent signaling

Answer 7

Cells make direct physical contact; signal molecules lodged in the plasma membrane of the signaling cell meet receptor proteins embedded in the plasma membrane of the target cell

Question 8

Describe how hormones activate their receptors. What are their receptors called and where are they located?

Answer 8

bind to nuclear receptor proteins, changing their conformations

these receptors can be in the cytosol or the nucleus

Question 9

How do hormones and their receptors affect cells?

Answer 9

The activated receptor/hormone complex binds to regulatory portions of genes, activating transcription

Question 10

Describe hormone response elements

Answer 10

A section of many genes, allows many genes to be regulated by the same protein

Question 11

Hormones typically regulate ___ sets of genes in different cell types

similar/different

Answer 11

different

Question 12

What does GPCR stand for?

Answer 12

G-protein coupled receptors

Question 13

Describe the structure of a GPCR

Answer 13

protein that crosses the membrane seven times by alpha helices

Question 14

Describe how GPCRs are activated

Answer 14

binding of extracellular signals to the GPCR activates it by causing a conformational change that allows it to bind to a G protein

Question 15

Describe G-proteins

Answer 15

membrane-bound, trimeric, and activated by GTP

Question 16

How do GPCRs transmit signals into the cell? (stop at subunit)

Answer 16

binding of a GPCR to a G protein causes it to release its GDP, which causes the G protein to bind GTP (because GTP is more concentrated)

Question 17

Describe the subunits of the G protein

Answer 17

there is an alpha subunit and a beta/gamma subunit

the alpha is a GTPase, but both can phosphorylate other things

each subunit is attached by lipid anchors to the plasma membrane

Question 18

What are the two things most commonly activated by GPCRs?

Answer 18

Adenylyl cyclase and phospholipase C

Question 19

Describe “second messengers”

Answer 19

small, rapidly diffusing molecules that are produced to amplify extracellular signals and leave the membrane to go into the cell

Question 20

Describe the production of the second messengers IP3 and DAG by GPCR

Answer 20

they are produced from the cleaving of inositol phospholipid by a phosphoipase C that was activated by a GPCR via a G protein called Gq

the IP3 portion leaves and the DAG portion stays

Question 21

What does IP3 do?

Answer 21

It opens calcium channels in the endoplasmic reticulum

Calcium then binds to calmodulin, enabling it to interact with a wide variety of target proteins, including CaM-kinases

Question 22

What does DAG do?

Answer 22

It recruits and activates a protein kinase C (PKC) that moved from the cytosol to the plasma membrane

Question 23

How is cAMP produced and degraded?

Answer 23

an adenylyl cyclase activated by a GPCR produces cAMP from ATP

cyclic AMP phosphodiesterase converts cAMP to AMP

Question 24

How much cAMP is normally in the cell?

Answer 24

Not much, because the cell wants to be able to respond to small increases

cAMP is broken down to AMP quickly

Question 25

What are three things that cAMP can do in the cell?

Answer 25

activate PKA’s (cyclic-AMP-dependent protein kinases) that can phosphorylate serines or threonines

lead to phosphorylation of transcription regulators

lead to glycogen breakdown and the inhibition of enzymes that drive glycogan synthesis

Question 26

What does RTK stand for?

Answer 26

receptor tyrosine kinases

Question 27

Describe RTKs

Answer 27

largest class of enzyme-coupled receptors, have a cytoplasmic domain that functions as a tyrosine protein kinase, which phosphorylates particular tyrosines on specific intracellular signaling proteins

Question 28

What are the two things most commonly activated by RTKs?

Answer 28

phospholipase C (the GPCR one) and Ras

Question 29

How are RTKs activated and inactivated?

Answer 29

binding of a signal molecule causes dimerization and activation of the two subunits which then phosphorylate each other on three sites, allowing other proteins to dock

the tyrosine phosphorylations can be reversed by protein tyrosine phosphatases or activated RTKs can be dragged to the interior of the cell by endocytosis and destroyed by lysosomes

Question 30

Describe the activation of PIP3 by RTKs

Answer 30

RTKs activate a PI 3-kinase (similarish to phospholipase C), which will activate IP3 by phosphorylation (now be called PIP3)

Question 31

What does PIP3 do?

Answer 31

PIP3 will act as a docking site for molecules like AKT to be recruited to the membrane and activated

Question 32

Describe the proteins Bad and BCl2 and their relationship to PIP3

Answer 32

BCl2 inhibits apoptosis, but is inactivated by an un-phosphorylated Bad

PIP3 activates AKT, which will phosphorylate Bad

Question 33

Describe apoptosis

Answer 33

programmed cell death; a normal part of development and a beneficial response to massive DNA damage

Question 34

Describe the protein Tor

Answer 34

it is activated by PIP3 and enhances protein synthesis and inhibits protein degradation

Question 35

Describe protein Ras

Answer 35

a GTPase that is active when bound to GTP and inactive when bound to GDP

lipid anchor to plasma membrane

Question 36

Describe the activation of Ras by RTKs

Answer 36

the RTK activates and allows docking of an adaptor protein, which activates a Ras-activating (Ras-GEF) that stimulates the release of GDP from Ras

causes Ras to replace GDP with GTP (GTP is more concentrated)

Question 37

How is Ras inactivated?

Answer 37

a protein called Ras-GAP promotes hydrolysis of GTP

Question 38

What does Ras do in the cell?

Answer 38

lead to a kinase cascade

MAP kinase kinase kinase activates MAP kinase kinase, which activates MAP kinase (also called MARK, mitogen activated protein kinase)

Question 39

How is Ras associated with cancer?

Answer 39

It is mutated, such as to be hyperactive