Block 2 - Intro to Cell Communication

Question 1

What are the 4 ways cells can communicate change?

Answer 1

contact dependent - signal molecule in one cell contacts receptor on another cell
paracrine - cell to signaling cell to target cell
synaptic - one cell contacts another cell via a synapse
endocrine - endocrine cell releases a hormone into the bloodstream that reaches a receptor on a target cell

Question 2

Certain specialized receptor cells respond to —– stimuli

Answer 2

external

Question 3

Cell communication often involves —– signals

Answer 3

chemical

Question 4

Chemicals that are produced in one cell that work over a distance to produce a response in a second cell are called…

Answer 4

hormones

Question 5

Peptide and protein signaling molecules can’t —– so they require —–

Answer 5

can’t cross the plasma membrane so they require a receptor on the cell’s surface

Question 6

True or False: only a single stimuli or receptor links to a given signaling pathway

Answer 6

False - many can link to the same pathway

Question 7

When a chemical signal reaches a cell, the response is often caused by…

Answer 7

• speeding up/slowing down a biochemical reaction
• increase/decrease a protein by altering transcription or translation
• change the activity of a protein by phosphorylation/dephosphorylation (post-translational modification)
• change the location of a protein
• start/stop the release of a secreted product

Question 8

What are the three classes of plasma membrane receptors?

Answer 8

ion channel linked receptors
g protein coupled receptors
enzyme linked receptors

Question 9

All plasma membrane receptors are…

Answer 9

integral membrane proteins

Question 10

What are GPCRs?

Answer 10

• g protein coupled receptors
• activate a class of GTP binding proteins (G proteins) which are molecular switches that turn on while bound to GTP and turn off by hydrolysis of GTP to GDP

Question 11

What are GTP and GDP?

Answer 11

guanosine triphosphate
guanosine diphosphate

Question 12

GPCR’s have —- transmembrane spans and associate with a —unit G protein

Answer 12

7 transmembrane spans
3 unit G protein

Question 13

When a ligand binds to the GPCR, what happens?

Answer 13

• GTP exchanges for GDP on the G protein
• alpha subunit dissociates from the complex and activates signaling pathways that bring about a cell response

Question 14

True or False: the dissociated alpha subunit of a G protein always activates the same pathway

Answer 14

False - they are associated with different receptors and can activate different signaling pathways

Question 15

G proteins can…

Answer 15

• regulate ion channels
• activate adenylate cyclase (increasing intracellular cyclic AMP)
• activate Phospholipase C (increasing intracellular IP3 and DAG)

Question 16

Increasing cAMP can lead to…

Answer 16

protein phosphorylation
- activates protein kinase A which leads to protein phosphorylation and many different types of cell response

Question 17

Protein Kinase A plays a role in phosphorylation, but also…

Answer 17

interacts with cAMP response element CREB to activate transcription (so it activates a transcription factor)

Question 18

Many stimuli rely on —– signaling to “get their messages through”

Answer 18

cAMP signaling

Question 19

What happens after GPCR signaling activates phospholipase C?

Answer 19

• IP3 is released into the cytosol
• Ca++ release from the ER is stimulated
• elevated Ca++ activates calcium-dependent protein kinases and phosphatases that alter the activity of target proteins

AND

• DAG is produced and remains in the membrane (because it is hydrophobic)
• DAG activates members of the protein kinase C family

Question 20

Most signaling molecules can’t —- so their receptors…

Answer 20

can’t pass through the cell membrane, so their receptors are in the cell membrane

Question 21

Some small hydrophobic signal molecules like steroids can —– so their receptors…..

Answer 21

can diffuse directly in to the cell cytoplasm so their receptors are cytoplasmic or nuclear

Question 22

True or False: a stimuli can only act at one site

Answer 22

False - certain stimuli can act at more than one site and have more than one response/effect

Question 23

Signaling pathways allow the response to….

Answer 23

be amplified, and cause a pattern of changes involving several different reponses

Question 24

Although cells have many ways to cause a reponse, it is also important that they can…

Answer 24

terminate a response, diminish responsiveness, and prevent overstimulation

Question 25

What are the 5 ways a cell can terminate response?

Answer 25

receptor sequestration
receptor down regulation
receptor inactivation
signaling protein inactivation
production of an inhibitory protein

Question 26

What are Arrestins and how do they work?

Answer 26

• cytosolic proteins that recognize agonist-activated receptors and bind to them
• makes the receptor inaccessible for G proteins
• receptor is targeted for internalization by clathrin-coated pits and then as vesicles, where they are either recycled or sent to be degraded