Cell signalling

Question 1

Name 4 reasons we use cell signalling?

Answer 1

Process information
Self preservation
Voluntary movement
Homeostasis

Question 2

What is meant by Endocrine Communication?

Answer 2

Hormones travel within blood vessels to act on a distant target cell

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Question 3

Explain what occurs during Hypoglycaemia?

Answer 3

Glucagon secreted by alpha cells in the islets of Langerhans (in pancreas)

Glucagon travels out of pancreas via blood vessels

Glucagon stimulates glycogenolysis and gluconeogenesis within the liver → increasing blood glucose levels

Question 4

What is meant by Paracrine Communication

Answer 4

Hormone acts on an adjacent cell

Question 5

Explain what happens in Hyperglycaemia?

Answer 5

Increased blood glucose - insulin secretion by beta cells in the Islets of Langerhans

Insulin has paracrine effects: Inhibiting glucagon secretion

Insulin also has endocrine effects on the liver

Question 6

What is meant by Autocrine Communication?

Answer 6

Signalling where molecule acts on the same cell

Question 7

How does an ionotropic receptor work?

Answer 7

Ligand binds to receptor protein

causes conformational change and substrate moves in along the concentration gradient

Question 8

How do G-protein coupled receptors work?

Answer 8

7-transmembrane receptor
Conformation changes when a ligand binds to it
This causes the g-protein to associate to the receptor resulting in GDP phosphorylated into GTP
The G-alpha subunit disassociates and can act as second messengers As well as the gamma beta subunit
Remains active as long as ligand is bound

Question 9

How do enzyme linked receptors work?

Answer 9

• ligand binding
• receptors cluster - conformational change
• Linked enzyme phosphorylates receptor
• binding of signalling proteins to cytoplasmic domain of receptor
• recruit other signalling proteins
• signal generated

Question 10

How to type 1 intracellular receptors work?

Answer 10

chaperone molecules - heat shock proteins

Once hormone binds to receptor, hsp dissociates
hormone-receptor complex forms a homodimer with another identical hormone-receptor complex

Homodimer translocates to nucleus where it binds to DNA and acts as a transcription factor

Question 11

How do type 2 intracellular receptors work?

Answer 11

Binding of hormone ligand - transcriptional regulation by activated hormone-receptor complex
Located within a nucleus often already bound to DNA

Question 12

What is an intracellular receptor?

What exerts their actions on these?

Answer 12

A transcription factor, involved in regulation of mRNA and protein synthesis

Steroid hormones as they are membrane permeable

Question 13

What is a G protein complex consisting of?

Answer 13

Alpha subunit

Beta-gamma subunit

Associated GDP molecule

Question 14

Example of an ionotropic receptor?

Answer 14

nicotinic acetyl choline
GABA a
NMDA

Question 15

What are three different types of Gprotein linked receptors and what do they do?

Answer 15

Gs - stimulates adenylyl cyclase ie β1adrenergic
converts ATP to cyclicAMP (CAMP)
CAMP activates protein kinase A (PKA)

Gi- Inhibits adenylyl cyclase ie M2-muscarinic receptor
reduces levels of PKA

Gq - stimulates phospholipase C (PLC) ie AT-1 angiotensin receptor

Converts PIP2 to IP3 and DAG
IP3 stimulates calcium release and DAG activates PKC

Question 16

Give some examples of enzyme linked receptors

Answer 16

Insulin receptor - CD220 antigen

ErbB receptors
epidermal growth factor receptor

Question 17

Give an example of a type 1 intracellular receptor and a type 2?

Answer 17

1. GC-R - cortisol

2. TRα - thyroxine