White - Cell Communication 1

Question 1

Signal Transduction

Answer 1

Cell-to-cell communication; must traverse from outside the cell to inside the cell; important in the development of an organism and for coordination of metabolism; absolutely required for multicellular organisms

Question 2

Fast Response

Answer 2

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

Question 3

Slow Response

Answer 3

Change in amounts of proteins by change in expression of genes

Question 4

Signal Transduction Process

Answer 4

Ligand binds to high affinity receptor, which produces intracellular signal proteins to interact with effector proteins; these effector proteins can alter metabolism, alter gene expression, or alter the shape and/or movement of the cell

Question 5

Endocrine Signaling

Answer 5

Long distance signaling; signal goes to blood stream and travels to distant target cells; long lasting because it takes time to go through the circulatory system to find a target cell

Question 6

Paracrine Signaling

Answer 6

Acts locally and affects nearby cells; short lived signals

Question 7

Synaptic Signaling

Answer 7

Acts locally and affects nearby cells; short lived signals (specifically neurotransmitters)

Question 8

Autocrine Signaling

Answer 8

Cells respond to signals that they themselves release or release to cells of the same type; cell secretes signal that feeds back and binds to a receptor on its own surface (growth factors); causes cells to grow, divide, and mature

Question 9

Direct Cell Signaling

Answer 9

Immune cells; Antigen presenting cells to T-cells

Question 10

Signals (Ligands)

Answer 10

Typically secreted by exocytosis and can stay near or far

Question 11

Receptors

Answer 11

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

Question 12

Effectors

Answer 12

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

Question 13

Nitric Oxide signaling is an example of what kind of signaling?

Answer 13

Paracrine signaling

Question 14

Cell Surface Receptors

Answer 14

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

Question 15

Intracellular Receptors

Answer 15

Steroid receptor can have receptor in cytosol (estrogen); alters gene expression in nucleus

Question 16

G Protein Coupled Receptors

Answer 16

Part of 2nd messenger system; has 3 parts (Extracellular domain, transmembrane domain, cytoplasmic domain); 7 transmembrane domains

Question 17

Extracellular Domain of GPCR

Answer 17

Binds to ligand

Question 18

Transmembrane Domain of GPCR

Answer 18

Anchors receptor

Question 19

Cytoplasmic Domain of GPCR

Answer 19

Associates with G-protein

Question 20

G-Proteins

Answer 20

Heterotrimeric proteins composed of 3 subunits (alpha, beta, gamma); impacts effector; also called guanine nucleotide-binding proteins

Question 21

GPCR Activity/Process

Answer 21

GPCR–> Trimeric G protein–> Effector enzyme–> 2nd messenger–> Targets of 2nd messenger–> Biological response

Question 22

Steps in G-Protein Relaying Signals

Answer 22

1. Ligand binds to receptor
2. Conformational change occurs in receptor
3. Receptor binds to G protein
4. Receptor acts as a Guanidine Exchange Factor (GEF)
5. Confirmation of G-alpha protein is changed such that it kicks out GDP and GTP binds to it
6. G-alpha now becomes active and can bind to effector molecule and activate effector molecule
7. Effector molecule in this case is adenylyl cyclase which catalyzes formation of cAMP

Question 23

How do you stop the G protein from relaying signals?

Answer 23

Hydrolyze GTP to GDP which returns G-alpha to inactive step to be recycled through process again

Question 24

What does adenylyl cyclase do?

Answer 24

Generates cAMP which goes on to interact with it’s target proteins to cause a biological response

Question 25

G-alpha-S Protein

Answer 25

Stimulates adenylyl cyclase

Question 26

G-alpha-I Protein

Answer 26

Inhibits adenylyl cyclase

Question 27

What does cAMP do?

Answer 27

Activates a protein kindase called PKA

Question 28

Desensitization

Answer 28

Ability to turn off or reject the signal; important in the cell cycle and development of cancer

Question 29

5 Ways to Desensitize a Signal

Answer 29

1. Receptor sequesteration (invagination of membrane and formation of endosome)
2. Receptor destruction (formation of endosomes and lysosomes to form proteases)
3. Hormone levels drop, which decreases adenylyl cyclase activity, which decreases cAMP, which decreases PKA activity
4. Remove the signaling molecule (phosphodiesterases will remove cAMP)
5. GRK’s (G Protein Receptor Kinases)

Question 30

GRK’s

Answer 30

Phosphorylate the receptor such that another protein called arrestin will bind to the 3rd intracellular loop of receptor and prevents G-alpha from interacting with the third loop of receptor; prevents G-alpha-GDP from becoming G-alpha-GTP