L8- Ca2+ signalling

Question 1

What are receptor tyrosine kinases?

Answer 1

• One transmembrane segment with an extracellular protein ligand binding domain
• Cross phosphorylation activation
• Tyrosine phosphatases terminate activation

Question 2

What are ligands for tyrosine kinases?

Answer 2

• Epidermal growth factor
• Insulin- glucose and lipid metabolism
• Vascular Endothelial Growth factor- angiogenesis
• Nerve Growth Factor

Question 3

What do the phosphorylated tyrosines act as?

Answer 3

Docking sites sites for interacting proteins.

Question 4

What are the RTK signalling pathways?

Answer 4

1. RTK’s evoke hydrolysis of PIP2 through phospholipase C activation
2. RTK’s evoke hydrolysis of PIP2 through PI3-kinase activation
3. RTK’s evoke dephosphorylation of PIP3 via PTEN

Question 5

What does PIP3 do?

Answer 5

Recruits Akt and PDK1 to the cell membrane

PDK1 phosphorylates Akt which phosphorylates Bad and inhibits apoptosis

Question 6

What is RAS and RAS-GEF?

Answer 6

RAS= a small monomeric G protein
GEF= Guanine exchange factor

Question 7

How is RAS activated y RTK?

Answer 7

RTK activation recruits RAS-GEF to adaptor protein

RAS-GEF activates RAS by stimulating exchange of GDP for GTP

Question 8

What does activated RAS do?

Answer 8

Stimulates Raf
Raf phosphorylates Mek
Mek phosphorylates Erk

Question 9

What is intracellular and extracellular Ca2+ concentration?

Answer 9

Ca2+ intracellular= 100mM

Ca2+ extracellular= 1.5mM-2.5mM

Question 10

What effectors does Ca2+ impact?

Answer 10

• Enzymes: Kinases, phosphatases, phospholipases

* Ion channels: K+, Cl-, TRP channels

Question 11

What does Ca2+ mediate?

Answer 11

• Contraction

* Hormone and transmitter release

Question 12

What are the Ca2+ and release pathways?

Answer 12

1. Ligand gated ion channels (NaChR, GluRs)
2. TRP channels
3. Voltage gated calcium channels
4. Conformational coupling
5. Calcium induces Ca2+ release
6. IP3R mediated Ca2+ release

Question 13

What is the order of speed of the Ca2+ pathways?

Answer 13

• RAPID- Voltage gated Ca2+ channels FAST
• VGCC to Ryanodine receptors
• Calmodulin, ion channels, kinases
• Ca2+/CaM- dependent kinase II
• Slow Ca2+ oscillations SLOW

Question 14

What are buffers?

Answer 14

Calcium binding proteins such as parvalbumin (slow) and calbindin (fast)
They mitigate fluctuations in intracellular calcium concentrations (excessive/decreases)1

Question 15

What transporters carry out Ca2+ sequestration and extrusion?

Answer 15

• Mt Ca2+ uniporter
• Na2+/Ca2+ exchangers
• SERCA
• PMCA

Question 16

How does calcium induced calcium release occur?

Answer 16

• Ryanodine receptors (RyR) are Ca2+ activated
• IP3R are Ca2+ activated in the presence of IP3 but are inhibited when intracellular calcium exceeds 300nM
• Modulation by cAMP, CAM etc

Question 17

What is CAM?

Answer 17

Calmodulin (CAM) is a ubiquitous and abundant Ca2+ sensor
• Ca2+/CAM interaction controls activity of numerous target proteins
• e.g CAM dependent kinases, phosphatases and ion channels