Cell signalling 1

Question 1

What is the basic concept of cell signalling?

Answer 1

A chemical released by 1 cell is recognised by another cell

• involves receptor molecule that recognises signal in a highly specific manner
  = allows recipient cell to respond

Question 2

Why is cell signalling important?

Answer 2

> essential for coordination of cell behaviour
single cell orgs use signalling to identify + interact w/ cells of correct mating type in sexual reproduction
multicellular orgs depend on signalling for correct development, tissue maintenance + homeostasis

Question 3

What happens if a cell doesn’t receive a survival signal?

What happens if signals are mis-regulated?

Answer 3

Undergoes apoptosis

Cancer

Question 4

What do insulin signals do when blood glucose rises after eating food?

Answer 4

Pancreatic beta cells secrete insulin
–> acts on adipose/muscle/liver cells
= glucose + amino acid uptake + storage

Question 5

How could problems with insulin signalling lead to diabetes?

Answer 5

Insufficient insulin production
= failure of pancreatic beta cells

Insulin insensitivity
= failed response of peripheral tissues

Question 6

What are the 4 main types of cell signalling systems?

Answer 6

> endocrine
paracrine
neuronal
contact-dependent (juxtacrine)

Question 7

What is endocrine signalling?

Answer 7

Endocrine cells release hormones that act on distant target cells in the body

Question 8

What is paracrine signalling?

Answer 8

Signal only goes short distance + acts on cells in same tissue or adjacent tissue

Question 9

What is neuronal signalling?

Answer 9

1 cell releases neurotransmitter molecules across a synapse

Question 10

What is contact-dependent signalling?

Answer 10

Signal only acts on touching adjacent cells

Question 11

How are neutrons + support cells formed during development?

Answer 11

Through contact mediated cell signalling involving Delta + Notch

Question 12

What is delta?

What is notch?

Answer 12

A membrane-bound inhibitory signal protein

A receptor protein

Question 13

What does neurogenin do?

Answer 13

Promotes the expression of delta signals

Question 14

Describe Delta-Notch signalling in neuronal differentiation

Answer 14

1. Unspecified epithelial cells signal to their neighbours to maintain low neurogenin levels
   = promotes low levels of Delta expression
2. By chance some cells will express higher levels of Delta
   -> signals to surrounding cells to prevent neurogenin expression
   = stops them from differentiating as neurones + reduces their expression of Delta
3. Neurogenin levels increase in cells NOT receiving Delta signal
   = allows expression of factors e.g. Neuro D
   = initiate neuronal differentiation

Question 15

What 3 mechanisms could be used to ensure local signals don’t act too far from their origin?

Answer 15

> rapid degradation
binding to inhibitory proteins
binding to ECM

Question 16

How does AcH affect heart muscle, salivary gland cells + skeletal muscle differently?

What are their receptors?

Answer 16

Heart = decreased rate of firing
receptor:GPCR

Salivary gland = secretion
receptor: GPCR

Skeletal = contraction
receptor: ligand-gated ion channel

Question 17

What can the molecular relay/ intracellular signalling pathway (initiated after signal-receptor interaction) allow?

Answer 17

> modulation of the signalling pathway e.g. cross-talk w/ other signalling pathways
amplification of the pathway
distribution of signal to all parts of cell

Question 18

What are the 2 examples of cell-surface receptors?

Answer 18

G-protein coupled receptors

Enzyme-linked receptors

Question 19

What are the 2 types of intracellular receptors + their examples?

Answer 19

> those that act as transcription factors
e.g. steroid + thyroid hormone receptors

> enzymes directly activated by the signal molecule
e.g. guanylyl cyclase activated by NO

Question 20

What are steroid + thyroid hormones?

Answer 20

Small, hydrophobic signal molecules that interact w/ intracellular receptors

–> hormone-receptor complex moves into nucleus + acts directly as a TF

Question 21

Which cells produce testosterone?

Answer 21

Leydig cells in testis

Question 22

What is androgen insensitivity syndrome?

Answer 22

XY individuals lack testosterone receptor

–> develop female physical characteristics

Question 23

What is NO used to treat?

Answer 23

Angina = pain associated w. poor blood flow to heart

Question 24

Which features of NO ensures it acts only locally?

Answer 24

Reacts readily w/ O2 + water to form nitrates/nitrites

Half life = 5-10 seconds

Question 25

Describe how NO is used to treat angina

Answer 25

1. Nerve terminal releases neurotransmitter + binds to receptor on endothelial cell
2. Signalling system in cell produces NO (from arginine)
3. NO fuses to smooth muscle cells
4. NO binds to target protein (guanylyl cyclase)
   = rapid relaxation of smooth muscle cell
   –> dilates blood vessel

Question 26

What happens when guanylyl cyclase is bound to NO?

How is this signalling reversed?

Answer 26

Converts GTP to cGMP
–> increased cGMP = smooth muscle cell relaxation
= blood vessels dilate

cGMP phosphodiesterase converts cGMP into 5’-GMP
–> muscle cells contract
= blood vessels constrict

Question 27

How does viagra work?

Answer 27

Inhibits PDE5 phosphodiesterase in the blood vessels of erectile tissue
= sustained signalling response
= blood vessels remain dialect