CMB1004/L16 Cell Signalling II Flashcards
What is the role of phospholipase C?
Cleaves PIP2 to produce IP3 and DAG
Why is PIP2 cleaved by phospholipase C? (2)
Secondary messenger products are soluble and able to initiate Ca2+ release
What is the role of IP3?
Causes Ca2+ release from endoplasmic reticulum
What is the role of DAG?
Works with Ca2+ to activate protein kinase C (PKC)
What is DAG?
Diacylglycerol
What is PIP3?
Phosphatidylinositol 4,5-bisphosphate
What is IP3?
Inositol 1,4,5-triphosphate
Why are small changes in Ca2+ concentration easily detected?
Cytosolic Ca2+ levels are maintained at a low level (10^-7M) compared to extracellular Ca2+ (10^-3M)
What protein are many Ca2+ effects mediated by?
Calmodulin
Describe the structure of calmodulin. (2)
Binds 4 Ca2+ ions
Long helical domain with 2 globular ends activated by binding of Ca2+
Describe the binding of calmodulin with its target proteins.
Conformational change by Ca2+ ions allow wrapping around and activation of target proteins
Describe the structure of enzyme linked receptors. (2)
Single-span transmembrane protein
Cytosolic domain has intrinsic enzymatic activity or is associated with an enzyme
What is the most common type of enzyme linked receptor?
Receptor tyrosine kinases
Name 2 receptors in the RTK (receptor tyrosine kinase) family.
Insulin receptor
Many growth factor receptors
What occurs immediately after binding of a ligand to growth factor receptors?
Cross-linking of two receptor chains
What allows cross-phosphorylation (autophosphorylation) of receptor chains in enzyme coupled receptors?
Oligomerisation of receptor chains
How does the insulin receptor act differently to other enzyme-linked receptors? (2)
They are tetramers
Ligand binding causes realignment of polypeptide chains activating cross-phosphorylation
What provides docking sites for signalling proteins?
Phosphorylated tyrosine residues
What is the main signal- transducer for growth factors?
Ras
Simply describe the structure of Ras.
Small, monomeric G-protein
Simply describe the process following ligand binding to a trimeric G-protein coupled receptor. (3)
Bind directly to receptor
Receptor activates GDP release
GTP hydrolysis by intrinsic GTPase activity alone
Simply describe the process following ligand binding to a monomeric (e.g. Ras) protein receptor. (3)
Not directly linked to receptor
GDP release activated by GEF (guanine nicleotide exchange factor)
Weak intrinsic GTPase activity - needs GAP to drive GTP hydrolysis
What is GAP?
GTPase activating protein
What is GEF?
Guanine nucleotide exchange factor
What mediates binding of RTK to RAS and GEF?
Adaptor protein Grb-2
What type of pathway is activated by Ras?
MAP-kinase pathway
Give the order of kinase enzymes in the Ras MAPK pathway (4).
Ras, Raf, Mek, Erk
What 2 processes occur in the Ras-MAPK pathway?
Phosphorylation
Amplification
What kind of protein is RAS?
Proto-oncogene
Gene normally involved in signalling and is mutated in cancer progression
What are the most common RAS mutations?
Reduction of GTP hydrolysis activity
What occurs in the BRAF V600E mutation in melanoma?
BRAF remains activated
Continuous signalling down pathway
Treated with inhibitor Vemurafenib
