Intracellular Signalling

Question 1

Ways a cell responds and examples

Answer 1

1. Change in metabolic activities
   Eg glucagon breaks down glycogen
2. Secrete and release
   Eg antigen binding to mast cell stimulates histamine release
3. Change in gene expression
   Epidermal growth factor -> cell growth
4. Sensory perception
   Light activation of rhodopsin

Question 2

Extracellular signals and examples

Answer 2

1. Aa
Eg adrenaline 
2. Steroids 
Eg testosterone 
3. Proteins
Eg insulin 
4. Gases 
eg CO

Question 3

5 ways cells signal to each other

Answer 3

1. Endocrine 
Signal travels in blood
2. Autocrine 
Acts on same cell that produces it
3. Paracrine
Acts on neighbouring cells 
4. Contact dependent 
Integral part of one cell interacts directly with another
5. Neuronal
Electrical signal passed through a synapse

Question 4

2 types of receptor and implications

Answer 4

1. Cell surface
   Hormone is hydrophilic
   Triggers response in cell
2. Intracellular
   Hormone is hydrophobic
   Crosses CM
   Binds to receptor inside cell

Question 5

4 things that can happen after signal binds to receptor

Answer 5

1. Membrane depolarisation
2. Activation of transcription factor
3. Secondary message
4. Activation of enzymatic kinase cascade

Question 6

How Steroid hormone receptors activate transcription factors

Answer 6

Steroid hormones have hormone binding domain/DNA binding domain/transcription factor domain
Binding of steroids-> conformational change-> DNA binding & transcription activation (ligand dependent transcription factors)

Question 7

3 Examples of secondary messenger formation

Answer 7

1. GPCR activates adenylyl cyclase-> cAMP formed

2. GPCR activates Phospholipase C-> ip3/DAG formed

Question 8

How G proteins work

Answer 8

3 subunits: alpha beta gamma
Signal binds to receptor -> G proteins associate with receptor-> gdp exchanged for GTP->
Alpha dissociates-> alpha activates effector enzymes
Reassociation when GTP hydrolysed to gdp

Question 9

camp dependent protein kinase a components and formation

Answer 9

Made of 2 catalytic and 2 regulatory subunits

Camp binds to R subunits-> tetramer dissociates-> c subunits are active enzymes

Question 10

Kinase cascade through glucagon receptor

Answer 10

Glucagon binds to glucagon receptor
ATP converted to camp
(Camp) activates PKA
(PKA) converts phosphorylase kinase b to a *ATP
(Phosphorylase kinase a) converts phosphorylase b to a *ATP
(Phosphorylase a) converts glycogen to glucose-1-phosphate

Question 11

Camp & gene transcription

Answer 11

PKA phosphorylates CREB (camp response element binding protein)
CREB binds to specific sequences in target genes, stimulating transcription

Question 12

How is DAG and IP3 produced, what do they do. Example

Answer 12

Alpha subunit that has dissociates from G protein activates Phospholipase C
Phospholipase C cleaves inositol phospholipids
IP3 / DAG produced
IP3 activates Ca2+ channel in ER-> ca2+ conc in cytoplasm increases-> DAG ANDd ca2+ activate PKC

Eg adrenaline receptor

Question 13

EGF- ras cascade

Answer 13

EGF binds to receptor-> autophosphorylation of Y residues in cytoplasmic domain (receptor tyrosine kinase) -> adaptor proteins SIS and GRB2 have ohosohotyrosine binding sites (SH2 and PTB) -> GDP ras -> gtp ras

Question 14

What’s ras

Answer 14

Monomeric G protein

GTP ras triggers kinase cascade
MAPKKK activates MAPKK which activates MAPK which activates transcription factor

Question 15

What’s convergence

Answer 15

Signals trigger Different pathways , same effect

Question 16

What’s cross talk

Answer 16

Different signals trigger diff pathways that block each other