General Principles of Cell Communication

Question 1

What are the 3 types of cell signalling?

Answer 1

Endocrine - widespread, effects many cells in the body
Autocrine - signal feeds back onto same cell
Paracrine - two cells close, simple diffusion, short distance

Question 2

All receptors do 2 things

Answer 2

Recognise a specific signal

Initiate a cellular response

Question 3

Explain the functionality of receptor tyrosine kinases

Answer 3

Responds to growth factors
Act in dimers
Kinase = phosphorylates intracellular proteins 
1st messenger binds to receptor 
Stimulates enzyme
Phosphorylates proteins

Question 4

What is the result of some mutations in receptors?

Answer 4

constitutive activity
activation in the absence of a ligand
If the ligand is a GF –> cancer

Question 5

Example of a ligand-gated ion channel
Why is it named this?
How does it work?

Answer 5

nicotinic acetylcholine receptor (nAChR)
5 subunits, Na+ pore through centre
Binds ACh on post-synaptic membrane, leads to depolarisation
Nicotinic - nicotine mimics ACh in brain –> addiction

Question 6

Example of a GPCR

Answer 6

Muscarinic acetylcholine receptors

Muscarine found in mushroom mimics ACh

Question 7

Define G protein and outline structure

Answer 7

heterotrimeric GTPases that transfuses effect from receptor to effector
7 transmembrane helices
Guanine nucleotide regulatory binding protein

Question 8

Which organisms to not have GPCR’s?

Answer 8

bacteria

Question 9

Outline the steps involved when a ligand binds to a GPCR

Answer 9

1) Ligand binds to GPCR
2) GPCR undergoes conformational change
3) alpha subunit exchanges GDP for GTP
4) alpha subunit detaches –> effect
5) GTP hydrolysed to GDP by GTPase within the subunit
6) alpha subunit reassociates

Question 10

How does the cholera toxin interact with GPCR’s to produce it’s effect?

Answer 10

decreases activity of GTPases
GTP binds irreversibly
prolonged activation of Gs
increased cAMP

Question 11

How does bordatella pertussis interact with GPCR’s to produce it’s effect (whooping cough)?

Answer 11

prevents GPCR interacting with g-protein (Gi)
No GDP dropping off
Prevents Gi inhibition so cAMP increases

Question 12

What converts ATP into cAMP?

How is the cAMP signal switched off?

Answer 12

adenylyl cyclase

cAMP phosphodiesterase converts cAMP into 5’AMP

Question 13

In what 2 ways can you increase cAMP?

Answer 13

activate adenylyl cyclase

inhibit cAMP-PDE

Question 14

What does cAMP do?

Answer 14

activates protein kinase A (PKA)

phosphorylates proteins

Question 15

What is phospholipase C and where is it found?

Answer 15

Effector of a GPCR
An enzyme
Phospholipid bilayer

Question 16

What happens when PLC is activated?

Answer 16

two 2nd messengers are formed
InsP3 - Inositol-1,4,5-trisphosphate
DAG - diacylglycerol

Question 17

Which type of Gprotein relay signals to phospholipase C?

Answer 17

Gq and G11

Question 18

What effect does InsP3 have?

What effect does DAG have?

Answer 18

InsP3 causes the release of calcium from intracellular stores
DAG activates membrane bound protein kinase C
These both lead to protein phosphorylation/dephosphorylation

Question 19

What is UDP?

What is UDP-Glc?

Answer 19

uridine diphosphate

glucose bound to UDP - the metabolically activated form of glucose

Question 20

What enzyme catalyses this reaction?

glycogen(n) + UDP-Glc –> glycogen(n+1) + UDP

Answer 20

glycogen synthase

Question 21

What enzyme catalyses this reaction?
What is the second product?
glycogen(n+1) + Pi –> glycogen(n) + Glc-1-P

Answer 21

glycogen phosphorylase

glucose-1-phosphate

Question 22

What do protein kinases do?

What do protein phospatases do?

Answer 22

• adds phosphate

- removes phosphate

Question 23

2 pathways in the enzyme cascade for glycogen metabolism

Answer 23

cAMP activates cAMP dependent protein kinase (PKA)
activates glycogen phosphorylase kinase
activates glycogen phosphorylase
–> glycogen
OR
cAMP activates cAMP dependent protein kinase (PKA) which activates glycogen synthase

Question 24

Effect of increased cAMP on glycogen metabolism

Answer 24

activates glycogen breakdown

inhibits glycogen synthesis

Question 25

Effect of decreased cAMP on glycogen metabolism

Answer 25

inhibits glycogen breakdown

Activates glycogen synthesis