Hormones and cell signalling

Question 1

Give an example of an autocrine factor

Answer 1

Growth factors

Question 2

Describe autocrine action

Answer 2

When a hormone has an affect on the cell that produced it

-Most effective when autocrine cells are in a group together as they receive a stronger signal

Question 3

What happens when a hormone bind to its nuclear receptor?

Answer 3

Hormone and receptor bind-> activated receptor-> active receptor binds to DNA-> regulates transcription of specific target genes
(in the presence of the hormone the nuclear receptor recruits additional coactivator proteins which regulate activation of nearby target genes.

Question 4

Are most signalling molecules hydrophobic or hydrophilic?

Answer 4

Hydrophilic- so cannot cross membrane directly but have to bind to surface protein

Question 5

What are the 3 zones of a receptor?

Answer 5

• Extracellular hormone binding domain
• Transmembrane domain
• Intracellular domain

Question 6

Describe the effects of a ligand binding to a receptor

Answer 6

When the ligand bind to the EXTRACELLULAR hormone binding domain it causes conformational changes in the cytoplasmic domain. This stimulates a signalling pathway. Often involves a protein kinase. The receptor then phosphorylates intracellular proteins.

Question 7

List examples of intracellular signalling molecules

Answer 7

ACTH, ADH, LH, FSH-> adenyl cyclase
ANP-> Guanylyl cyclase
TRH, GnRH->Phospholipase C
insulin, prolactin, IGF, Growth hormone-> Tyrosine kinase

Question 8

List different cell surface receptors

Answer 8

• Ion channel linked
• G protein linked
• Tyrosine linked
• Receptors with intrinsic enzymatic activity

Question 9

What is the action of ion channel linked receptors?

Answer 9

Rapid synaptic signalling

• Ions move passively by diffusion
• Changes the excitability of the post synaptic cell
  e. g. GABA receptors/ Nicotinic Ach receptors

Question 10

What is the action o f G protein linked receptors?

Answer 10

Indirectly activate a separate plasma membrane bound protein, single polypeptide chain that spans membrane 7 times
e.g. ACh receptor -> binding of ligand recruits G protein complex-> GTP replaces GDP and regulates secondary messengers

Question 11

What is the action of tyrosine kinase linked receptors?

Answer 11

Directly associates with the enzyme they activate

Question 12

What are second messenger signalling molecules?

Answer 12

Small intracellular signalling molecules
They are generated in large numbers by receptor activation.
They amplify the signal and pass it on by binding to and altering the behaviour of other proteins.

Question 13

How are proteins phosphorylated and how is it reversed?

Answer 13

• Phosphorylated by protein kinase enzymes

- Reversed by phosphoprotein phosphatase

Question 14

What is signal transduction?

Answer 14

-Adding/ removing phosphate groups

Question 15

What is down the adenylate cyclase system?

Answer 15

• Subunit of G protein activates the adenylate cyclase
• Adenylate cyclase causes the conversion of ATP to cAMP
• cAMP activates protein kinase A
• Protein kinase A = part of cascade of intracellular phosphorylations

Question 16

What receptor does insulin like growth factor 1 use?

Answer 16

Tyrosine kinase linked receptors

Question 17

What is the Ras pathway?

Answer 17

-A signal transduction pathway from tyrosine kinase receptors
Ligand and receptor binding triggers RAs-> leads to a series of protein kinases which activate transcription factors and result in a cellular response

Question 18

What are the two main classes of molecular switch?

Answer 18

• Phosphorylation

- GTP binding

Question 19

What is the proper name for the G protein?

Answer 19

Guanine nucleotide binding protein

Question 20

Describe growth factor activation of tyrosine kinase receptors

Answer 20

• The tyrosine kinase changes ATP- ADP

- Causes a change in charge and polarity