WEEK 4

Question 1

what are the 3 steps of signalling

Answer 1

1. signal reception
2. transduction
3. response

Question 2

types of intercellular signalling

Answer 2

direct cell to cell:

• junctions (gap and plasmodesmata)
• cell-cell recognition - receptors on membrane

local signalling:

• paracrine - cells in the same tissue via local regulators secreted via vesicles
• synaptic signalling - nerve electric impulse - neurotransmitter release

long distance:
- endocrine - hormones can be gas, lipid soluble or water soluble

Question 3

what are the 2 types of cell receptors and how do they operate

Answer 3

Ligand gated ion channel
- signal binds –> channel opens –> ions flow –> channel closes at the end of signal

G-protein coupled receptors:
→ Signal molecule binds to receptor
→ Receptor shape changes
→ allows G-protein to bind
→ G protein activated via hydrolysis of GTP
→ G-Protein activates an enzyme that triggers a cellular response
→ G-Protein deactivated by hydrolysis of GTP
→ signalling system turns off and resets

Question 4

what is the main method of signal transduction and 2 examples and what are the benefits

Answer 4

secondary messengers - intracellular signal molecule activated following receptor activation by first messenger

allows for amplication of signal
, control
and multiple responses

e. g. Ca2+
- causes tropomyosin to expose myosin binding site on actin microfilament allowing for muscle contractions
- can bind to calimodulin which activates other proteins

Kinesin enzyme
- phosphorylation enzyme - adds phosphate
- acts as on/off switch
- Phosphorylation Cascades (series of phosphorylation) → allows for amplification
→ Amplification - small initial signal massively increased

Question 5

what are some responses that can occur and how fast are they

Answer 5

• altered metabolism (fast)
• altered gene expression - growth factors (slow)
• altered cell movement - muscle, phagocytosis (fast)
• adrenaline (fast)