CMB1004/L16 Cell Signalling II

Question 1

What is the role of phospholipase C?

Answer 1

Cleaves PIP2 to produce IP3 and DAG

Question 2

Why is PIP2 cleaved by phospholipase C? (2)

Answer 2

Secondary messenger products are soluble and able to initiate Ca2+ release

Question 3

What is the role of IP3?

Answer 3

Causes Ca2+ release from endoplasmic reticulum

Question 4

What is the role of DAG?

Answer 4

Works with Ca2+ to activate protein kinase C (PKC)

Question 5

What is DAG?

Answer 5

Diacylglycerol

Question 6

What is PIP3?

Answer 6

Phosphatidylinositol 4,5-bisphosphate

Question 7

What is IP3?

Answer 7

Inositol 1,4,5-triphosphate

Question 8

Why are small changes in Ca2+ concentration easily detected?

Answer 8

Cytosolic Ca2+ levels are maintained at a low level (10^-7M) compared to extracellular Ca2+ (10^-3M)

Question 9

What protein are many Ca2+ effects mediated by?

Answer 9

Calmodulin

Question 10

Describe the structure of calmodulin. (2)

Answer 10

Binds 4 Ca2+ ions
Long helical domain with 2 globular ends activated by binding of Ca2+

Question 11

Describe the binding of calmodulin with its target proteins.

Answer 11

Conformational change by Ca2+ ions allow wrapping around and activation of target proteins

Question 12

Describe the structure of enzyme linked receptors. (2)

Answer 12

Single-span transmembrane protein
Cytosolic domain has intrinsic enzymatic activity or is associated with an enzyme

Question 13

What is the most common type of enzyme linked receptor?

Answer 13

Receptor tyrosine kinases

Question 14

Name 2 receptors in the RTK (receptor tyrosine kinase) family.

Answer 14

Insulin receptor
Many growth factor receptors

Question 15

What occurs immediately after binding of a ligand to growth factor receptors?

Answer 15

Cross-linking of two receptor chains

Question 16

What allows cross-phosphorylation (autophosphorylation) of receptor chains in enzyme coupled receptors?

Answer 16

Oligomerisation of receptor chains

Question 17

How does the insulin receptor act differently to other enzyme-linked receptors? (2)

Answer 17

They are tetramers
Ligand binding causes realignment of polypeptide chains activating cross-phosphorylation

Question 18

What provides docking sites for signalling proteins?

Answer 18

Phosphorylated tyrosine residues

Question 19

What is the main signal- transducer for growth factors?

Answer 19

Ras

Question 20

Simply describe the structure of Ras.

Answer 20

Small, monomeric G-protein

Question 21

Simply describe the process following ligand binding to a trimeric G-protein coupled receptor. (3)

Answer 21

Bind directly to receptor
Receptor activates GDP release
GTP hydrolysis by intrinsic GTPase activity alone

Question 22

Simply describe the process following ligand binding to a monomeric (e.g. Ras) protein receptor. (3)

Answer 22

Not directly linked to receptor
GDP release activated by GEF (guanine nicleotide exchange factor)
Weak intrinsic GTPase activity - needs GAP to drive GTP hydrolysis

Question 23

What is GAP?

Answer 23

GTPase activating protein

Question 24

What is GEF?

Answer 24

Guanine nucleotide exchange factor

Question 25

What mediates binding of RTK to RAS and GEF?

Answer 25

Adaptor protein Grb-2

Question 26

What type of pathway is activated by Ras?

Answer 26

MAP-kinase pathway

Question 27

Give the order of kinase enzymes in the Ras MAPK pathway (4).

Answer 27

Ras, Raf, Mek, Erk

Question 28

What 2 processes occur in the Ras-MAPK pathway?

Answer 28

Phosphorylation
Amplification

Question 29

What kind of protein is RAS?

Answer 29

Proto-oncogene
Gene normally involved in signalling and is mutated in cancer progression

Question 30

What are the most common RAS mutations?

Answer 30

Reduction of GTP hydrolysis activity

Question 31

What occurs in the BRAF V600E mutation in melanoma?

Answer 31

BRAF remains activated
Continuous signalling down pathway
Treated with inhibitor Vemurafenib