cell cycle

Question 1

5 stages of signalling cascades

Answer 1

response to EC factors -> signal amplification -> signal integration -> modulation by other pathways -> regulation of divergent responses (e.g. metabolic pathway, gene expression, cytoskeleton)

Question 2

2 examples of dimeric peptide growth factor ligands which bind and activate receptors (e.g. promoting cell cycle at G1)

Answer 2

epidermial growth factor (EGF), platelet-derived growth factor (PDGF)

Question 3

what are inactivated receptors found as

Answer 3

monomeric, inactive state

Question 4

in presence of a ligand, what happens to the receptor

Answer 4

forms dimers, activating receptor protein tyrosine kinase (RPTK) domain by cross-phosphorylating amino acid residues on each other

Question 5

how does protein phosphorylation of serine, threonine and tyrosine (amino acids with exposed OH group) occur, and what enzyme catalyses it and reverses it

Answer 5

transfer of phosphate group from ATP to hydroxyl groups (by protein kinase); reversed by protein phosphatases

Question 6

2 ways in which the added phosphate group (-ve charge) can alter protein function

Answer 6

causes a conformational change in shape, leading to change in activity; creates a docking site for another protein

Question 7

what does receptor activation, by phosphorylated amino acids, trigger

Answer 7

kinase cascades and binding of adaptor proteins

Question 8

frequently, what is the protein regulated by a kinase, and what does this lead to

Answer 8

another kinase, so causes multiple phosphorylations and leads to signal amplification, diversification and opportunity for regulation (reversed by protein phosphatases)

Question 9

what activates the EC signal-regulated kinase cascade (ERK)

Answer 9

Ras (activated by GTP)

Question 10

describe general ERK cascade

Answer 10

activated Ras -> activates kinase 1 -> kinase II [ATP->ADP] -> kinase III [ATP->ADP]

Question 11

kinase I specific to ERK

Answer 11

Raf

Question 12

kinase II specific to ERK

Answer 12

MEK

Question 13

kinase III specific to ERK

Answer 13

ERK

Question 14

what is B-raf, and when is it mutationally activated

Answer 14

oncogene, mutationally activated in melanomas

Question 15

what do protein kinases stimulate

Answer 15

change in cell proteins and gene expression to promote division

Question 16

example of cell protein which promotes cell proliferation

Answer 16

c-Myc (phosphorylated and inputs directly into cell cycle)