Cell Signalling

Question 1

what is cell signalling

Answer 1

process of cellular communication -> allows us to function as organisms

Question 2

autocrine extracellular signalling

Answer 2

cell targets itself
- often involved in signal amplification (+ve feedback) and attenuation (-ve feedback)
- e.g. inflammatory cell activating itself with IL2

Question 3

endocrine extracellular signalling

Answer 3

cell targets distant cell through bloodstream
- e.g. glycemia regulation
- usually hormones

Question 4

juxtacrine extracellular signalling

Answer 4

cell targets neighbouring cell by direct contact -> via ligand, receptor, or GAP junction
- e.g. antigen presentation + cardiac contraction

Question 5

paracrine extracellular signalling

Answer 5

cell targets neighbouring cell without direct contact
- across synapses

Question 6

extracellular signalling molecules (1st messengers)

Answer 6

• growth factors
• neurotransmitters
• hormones (endo + para)
• cytokines
  synthesised + secreted by signalling cells
• specific response occurs in target cells with specific receptors

Question 7

4 main classes of receptors

Answer 7

• ligand gated ion channel
• g-protein coupled receptor (GPCR)
• kinase-linked receptor
• nuclear receptor

Question 8

ligand gated ion channel (ionotropic receptors)

Answer 8

• very fast binding and channel opening
• involved in fast synaptic transmission
• ligand binding site is on extracellular side

Question 9

ligand gated ion channel example

Answer 9

nicotinic ACh receptor (nAChR)
- permeable to Na+ and K+
- Na+ in and K+ out -> membrane depolarisation
- found at NMJ for muscle contraction

Question 10

g protein coupled receptor (GPCR)

Answer 10

• largest family
• second messenger coupled
• slower than ligand gated ion channel
• coupled to intracellular g protein

Question 11

GPCR example

Answer 11

stimulated by light, hormones, neurotransmitters
- adenoreceptors
- angiotensin II receptors
- muscarinic Ach receptor

Question 12

kinase-linked receptor

Answer 12

• large, heterogenous group
• one transmembrane domain
• mostly function as dimers
• ligand and dimerisation leads to phosphorylation

Question 13

kinase-linked receptor example

Answer 13

catalytic receptors = autophosphorylation
- e.g. insulin receptor
non-catalytic receptors (cytokines)
- e.g. IL-2 + IL-6

Question 14

nuclear hormone receptor

Answer 14

• intracellular receptors in cytosol or nucleus
• ligand-activated transcription factors
• regulate gene transcription
• seperate ligand and DNA binding sites

Question 15

nuclear hormone receptor examples

Answer 15

• steroid hormones
• thyroid hormones

Question 16

signal transduction steps

Answer 16

1. first messenger
2. receptor
3. second messenger
4. response

Question 17

singal transduction - liver cell example

Answer 17

first messenger = adrenaline
receptor = beta-adrenergic receptor
response = breakdown of glycogen into glucose

Question 18

are second messengers short or long lived intracellular signalling molecules

Answer 18

short-lived as can terminate response?

Question 19

how do second messengers allow for transduction and amplification

Answer 19

through quick increase in concentration after cell stimulation

Question 20

what are the 4 classes of second messengers

Answer 20

• cyclic nucleotides (cAMP, cGMP)
• membrane lipid derivatives (DAG)
• Ca2+
• gas (NO + CO)

Question 21

can some second messengers be first messengers

Answer 21

yes (depends on hierarchy of events)

Question 22

pathway specificity

Answer 22

multiple factors influence response of one cell to one signal

Question 23

pathway complexity

Answer 23

many pathways allow multiple responses

Question 24

type I diabetes

Answer 24

destruction of pancreatic B cells (autoimmune)
- message is lost so nothing for receptor to detect so GLUT4 doesn’t open

Question 25

type II diabetes

Answer 25

message ignored by receptor - GLUT4 doesn't open

Question 26

Myasthenia Gravis

Answer 26

autoantibodies traget ACh receptors at NMJ - no Na+ into post synaptic cleft so no muscle contraction