Unit 8 - Cell Communication

Question 1

Why do single-celled organisms need to communicate?

Answer 1

• social life, yeast mating

Question 2

PLAY
Why do single-celled organisms need to communicate?
-social life (yeast mating)
Why do multi-cellular organisms need to communicate (

Answer 2

1. Day-to-day physiology
2. Coordination of development
3. Coordination of growth

Question 3

Signalling Pathway

Answer 3

1. signalling molecule is synthesized and released by the signalling cell
2. signal molecule travels to target cell
3. signal binds to receptor protein on/in target cell
4. changes in protein activity, gene expression, cell movement, shape, metabolism, secretion

Question 4

Steroid Hormone Mechanism of Action

Answer 4

• receptors on steroids are members of nuclear receptor family of transcription factors
• activated receptor-steroid complex binds to regulatory region of target gene –> activates transcription

Question 5

Intracellular Signalling Cascade

Answer 5

1. Primary Transduction
2. relay
3. transduce and amplify
4. integrate
5. distribute

Question 6

Second Messenger

Answer 6

small, non-protein molecule, relays signals from cell surface receptors to target molecules within the cell

Question 7

Kinase/Phosphotase

Answer 7

molecular toggle switch:

1. activation of kinase changes shape of target protein 2. phosphorylation causes target protein to become active 3. phosphatase removes Pi
2. target protein is back in inactive form, original shape

Question 8

GDP/GTP

Answer 8

Molecular Toggle Switch:

1. G-protein bound to GDP = inactive
2. G-protein changes shape, drops GDP, picks up GTP
3. G-protein bound to GTP = active
4. GTPase changes GTP –> GDP, back to inactive form

Question 9

serine/threonine kinases

Answer 9

phosphate hydroxyl groups of serine and threonine in a particular sequence

Question 10

Receptor Tyrosine Kinase (RTK)

Answer 10

• largest class of enzyme-coupled reactions
• signal proteins recruited to cytosolic tails of RTKs, activates downstream signals
• activate Ras

Question 11

G - protein

Answer 11

1. turn themselves off by hydrolyzing GTP to GDP
2. dissociation of GDP and replacement with GTP is in response to a signal
3. active form activates downstream steps in cascade

Question 12

Ion Channel-Coupled Receptors

Answer 12

• binding of ligand opens/closes ion channel

- flow of ions changes voltage across membrane

Question 13

GPCRs

Answer 13

-binding of ligand activates G-proteins, activates enzyme/ion channel in membrane which sets off cascade

Question 14

How long does G-protein signal last?

Answer 14

-usually a few seconds, as long as the alpha and beta subunits are free

Question 15

Consequences of disruptions in G-alpha function

Answer 15

1. cell is continuously active –> prolonged secretion into the gut
2. whooping cough –> bacterium colonizes lung, inappropriate signal that generates coughing

Question 16

what are downstream targets of G-proteins?

Answer 16

1. ion-channels

2. membrane-bound enzymes

Question 17

Cyclic AMP

Answer 17

• adenylyl cyclase is activated by GPCRs

- ATP is added, produces cyclic AMP which acts as a second messenger

Question 18

Ca2+ (intracellular signal)

Answer 18

1. concentration in cytosol very low compared to outside of cell
2. increased with opening of channels –> rapid signal
3. binding Ca2+ activates many different proteins
4. Activates Calmodulin (CaM)

Question 19

Ras

Answer 19

• GTP binding protein
• small, monomeric
• bound to inner membrane by lipid tail
• molecular switch, active when bound to GTP
• sets off relay of signals

Question 20

Mutations in Ras can lead to…

Answer 20

permanently activated proteins = cancer, most commonly mutated gene in human cancer cells