Cell signalling (5)

Question 1

Why do cells need to communicate?

Answer 1

1. process information- sensory stimuli e.g. sight, sound
2. self-preservation- identify danger e.g. spinal reflexes, sympathetic nervous system
3. voluntary movement
4. homeostasis- e.g. thermoregulation

Question 2

What is endocrine signalling?

Answer 2

hormone travels within blood vessels to act on a distant target cell

• intercellular signalling
• e.g. insulin, adrenaline, glucagon

Question 3

What is paracrine signalling?

Answer 3

hormone acts on an adjacent cell

• intercellular signalling
• e.g. insulin inhibiting glucagon secretion from alpha cells in islets, osteoclast activating factors produced by adjacent osteoblasts

Question 4

What is signalling between membrane-attached proteins?

Answer 4

plasma membrane proteins on adjacent cells interacting

• intercellular signalling
• e.g. TCR interacting w/ MHC

Question 5

What is autocrine signalling?

Answer 5

signalling molecule acts on same cell

• intercellular signalling
• e.g. activated T-cell secretes IL-2, which binds to IL-2 receptor on same cell

Question 6

What type of signalling is neurotransmission?

Answer 6

specialised paracrine
initial cell= presynaptic axon terminal
adjacent cell= usually post-synaptic cell
NT binds to receptors on psm and receptors modulate activity

Question 7

What are ionotropic receptors?

Answer 7

• intracellular
• ligand/hormone binds–> changes conformation of protein–> opens ion permeable pore–> allows movement of ions across membrane
• e.g. nicotinic acetylcholine receptor

Question 8

What is a G-protein coupled receptor (GPCR) and how does it work in detail?

Answer 8

hormone/ligand binds to external surface–> changes conformation of receptor–> allows G-protein heterotrimer to bind to internal surface of receptor–> bound GDP exchanged for GTP–> G-protein dissociates into 2 active components: alpha subunit w/ GTP molecule and beta-gamma subunit–> bind to target proteins–> internal GTPase dephosphorylates GTP to GDP–> alpha subunit dissociates from target protein and rejoins w/ beta-gamma subunit–> inactive again

Question 9

What is an enzyme linked receptor?

Answer 9

ligands bind–> receptor clustering–> activates internal enzymes–> phosphorylate receptor–> these signalling proteins recruit others

Question 10

What is an intracellular receptor?

Answer 10

special hormone crosses cell membrane and acts binds to receptor INSIDE cell–> ligand-receptor complex=transcription factor
- type 1 e.g. glutocorticoid receptor (located in cytoplasm, associated w/ chaperone molecules) and type 2 e.g. thyroid hormone receptor (located w/in nucleus)

Question 11

What does a heterotrimeric G-protein comprise?

Answer 11

Galpha and Gbetagamma

and GDP

Question 12

What are the 3 main categories of G-protein alpha subunit and what are their intracellular signalling pathways?

Answer 12

G alpha s- stimulates adenylyl cyclase–> converts ATP to cAMP–> activates protein kinase A (PKA)
G alpha i- inhibits adenylyl cyclase–> reduces PKA levels
G alpha q- stimulates phospholipase C (PLC)–> converts PIP2 to IP3 (stimulates calcium release) and DAG (activates PKC)