Cell Communication

Question 1

Why is cell communication important?

Answer 1

It is important for cell death, cell division, specification, and mating in yeast.

Question 2

What is Quorum Sensing

Answer 2

communication among bacteria, coordinates cell behaviors, signal is released and when it exceeds threshold concentration, signal reception and signal transduction cause gene expression.

Question 3

What are the forms of intercellular signaling?

Answer 3

Contact dependent, paracine (neighbor, stimulation, tissue); autocrine (self stimulation), synaptic (neuronal), endocrine (hormones, blood)

Question 4

Describe intracellular communication -

Answer 4

signal transduction occurs through kinases and phosphotases.

Question 5

What is signal transduction?

Answer 5

conversion of one signal to another

Question 6

What are ligands?

Answer 6

Molecules that stimulate a response in the target cell. Can be cell surface bound or hydrophobic and bind intracellular receptors.

Question 7

What are morphogens?

Answer 7

An extracellular signaling molecule that causes cells to have different fates based on their level of exposure to the signal.

Question 8

Where receptors located?

Answer 8

On the cell surface or intracellularly.

Question 9

How do multiple signaling molecules regulate cells?

Answer 9

Combinations of signaling molecules are integrated to control cellular processes. Same signal does not equal the same cellular decision in every cell type.

Question 10

What causes one signaling molecule to have varied responses?

Answer 10

Different receptors and different intracellular signals.

Question 11

Describe speed of response in endocrine and synaptic signaling.

Answer 11

Endocrine signaling has a slow response diffusing in blood. The ligand acts in low concentrations and the receptor has a high affinity for it.
In synaptic signaling, the response is rapid, the ligand is in high concentrations and the receptor has a low affinity for it.

Question 12

What’s the difference between signals that alter protein function and those that use transcription and translation to alter protein synthesis?

Answer 12

Altering protein function is quicker.

Question 13

What do protein kinase and protein phosphatase do?

Answer 13

Protein kinase adds a phosphate group through conversion of ATP to ADP. Protein phosphatase causes removal of phosphate group.

Question 14

What causes a signaling molecule to be on or off?

Answer 14

GTP bound molecules are on, GDP bound molecules are off.

Question 15

What are the types of cell surface receptors?

Answer 15

Ion channel coupled receptors, G-protein-coupled receptors, and Enzymes coupled receptors.

Question 16

What are g protein coupled receptors?

Answer 16

Signal molecules are Molecules for taste and smell, Neurotransmitters, Hormones, Light.
Receptors have 7 pass transmembrane proteins, use trimeric or monomeric (ran, rho, rac, ras) g proteins to relay signal.

Question 17

Describe trimeric G proteins -

Answer 17

Anchored in the cytoplasmic face of plasma membrane by lipids. • Composed of 3 subunits • GDP bound = Inactive • GTP bound = Active

Question 18

Describe activation of g protein -

Answer 18

• Activated GPCR functions like GEF to drive exchange of GTP for GDP on G protein.

*GTP activates the A subunit.
• One GPCR can activate many G proteins.
• Activation results in conformational changes that allow interaction of α subunit and βγ complex with targets.
. • Hydrolysis of GTP by α subunit returns G protein to inactive state. (Helped by GAP)

Question 19

What does adenylyl cyclase do?

Answer 19

It is an effector enzyme activated by 1 G protein. Stimulatory g proteins activate it, and inhibitory g proteins inhibit adenylyl cyclase.
Adenylyl cyclase catalyzes the production of cyclic AMP from ATP. cAMP activates protein kinase A.

Question 20

What does cAMP do?

Answer 20

Produced from ATP using adenylyl cyclase.

It is a second messenger and a small intracellular mediator formed/released in response to an extracellular signal.

It relays signaling in the cell. cAMP phosphodiesterase destroys cAMP to stop signaling.

Question 21

What is pKA?

Answer 21

PKA: cAMP-dependent protein kinase
• Composed of 2 regulatory and 2 catalytic subunits •cAMP binding to regulatory subunits causes conformational change and activation of catalytic subunits

Question 22

Describe CREB -

Answer 22

phosphorylation by pKA activates it, causing it to bind to CBP and activate the target gene, resulting in gene transcription.

Question 23

Describe amplification:

Answer 23

Amplification of a signal can occur at many points in a signaling pathway. Enzyme catalyzed steps are amplification steps.

Question 24

Describe desensitization to signals.

Answer 24

Altered ability of a cell to respond to a stimulus over time. Results in pathway turning off.

Question 25

how does desensitization occur?

Answer 25

• GPCR kinases (GRKs) activated by GPCR signaling
• GRKs phosphorylate GPCRs
• Arrestin recruited to sites of phosphorylation
• Prevents receptor interaction with G proteins and promotes endocytosis of receptor

Question 26

How is phospholipase c activated and what happens when it is activated?

Answer 26

Phospholipase c is activated by a G protein, causing diacylglycerol and IP3 to be formed. IP3 binds to Ca2+ channel in ER lumen, releasing Ca2+ and activating Protein kinase C along with diacylglycerol.

Question 27

What does Ca2+ function as?

Answer 27

It is a second messenger that increases in the cytosol after an extracellular signal, causing smooth muscle contraction, NT release, and glycogen breakdown.

Question 28

Describe intracellular receptors-

Answer 28

require small and/or hydrophobic ligands which can diffuse through the membrane.

Question 29

How do endothelial cells and NO cause relaxation of smooth muscle cells?

Answer 29

Endothelial cells bind signaling molecules (Ach), which promotes production of NO. NO binds to guanyl cyclase converting GTP to cyclic GMP, causing relaxation of smooth muscle cell.

Question 30

What do hormones do?

Answer 30

They are intracellular signaling molecules that bind nuclear receptors to influence transcription of target genes.

Question 31

Describe nuclear receptors -

Answer 31

can be inactive or active, binding of receptors to DNA causes transcription of target genes.