Receptors and Signalling II

Question 1

How do enzyme linked receptors work?

Answer 1

Ligand docks to the receptor and undergoes some kind of change causing the activation of an intrinsic enzyme

Question 2

What is the role of Receptor Tyrosine Kinases (RTKs)?

Answer 2

Phosphorylate proteins/molecules on their tyrosine residues
- Mitogen signalling usually involves RTKs (induction of cell division or cell growth)

Question 3

How do RTKs work?

Answer 3

RTKs are a single pass transmembrane protein - signalling cascade is initiated by ligand-induced dimerisation of receptors (most cases)
The ligand beinds to two receptors prodicing a monomer-monomer bridge (dimerisation)
The receptors then autophosphorylate each other, using their tyrosine kinase domains

Question 4

What does autophosphorylation of RTKs cause?

Answer 4

Phosphorylation creates a number of docking sites to specifically bind intracellular signalling proteins - these proteins bind to the docking sites thus prodcuing a large signalling complex

Question 5

What is the role of Ras (activated by RTKs)?

Answer 5

Causes activation of the MAP kinase cascade in whcih Ras activate MAPKKK. MAPKKK then phosphorylates MAPKK which then phosphorylates and activates MAPK which causes changes in gene expression leading to proliferation

Question 6

How is the Ras signal turned off?

Answer 6

1. Ras intrinsice GTPase converts GTP to GDP leading to its automatic deactivation
2. This is accelerated by a GTPase-activating protein (GAP), which is also recruited to the active receptor

Question 7

What is mitogenesis?

Answer 7

Fundamental mechanism by which all organisms propagate
Unicellular = New organism
Multicellular = requires lots of rounds to produce new individual but cell division required to replace old cells

Question 8

What are the stages of M phase (Mitosis) and Interphase?

Answer 8

Mitosis:
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Interphase:
- Cell Growth
- DNA replication