signal transduction pathways and hormone signalling

Question 1

how are cellular responses to signals achived?

Answer 1

typically, the signal binds to a cell surface receptor and the resulting conformational change stimulates a signal transduction pathway
-signal transduction pathways may involve a cascade of intracellular kinases or generation of intracellular signals called second messengers

Question 2

receptor tyrosine kinases

Answer 2

enzyme-linked receptors that recognise various types of signaling molecule
epidermal growth factor is a signalling molecule that binds to the EGF receptor to stimulate cell growth and division

Question 3

g-protein-coupled receptors

Answer 3

• “the first messenger” signals that bind to the cell surface receptors
• binding of signals to GPCRs often lead to the production of intracellular second messengers
• second messengers relay signals inside cells and include: cAMP, Ca+, Diaclglycerol (DAG), inositol triphosphate (IP3)

Question 4

signal transduction via cAMP

cAMP= cyclic adenosine monophosphate

Answer 4

activation of GPCR by siganlling molecule stimulates GTP binding by Gα subunit releasing it from Gβγ
α subunit binds to and activates adenylyl cyclase enzyme, stimulating cAMP synthesis

Question 5

cAMP activates protein kinase A (PKA)

Answer 5

the binding of cAMP to PKA activates the kinase enzyme activity
activated PKA phosphorylates specific intracellular proteins, including enzymes, structural proteins and transcription factors- resulting in a cellular response

Question 6

what are the advantages to second messengers

Answer 6

signal amplification- binding of the signal to one receptor molecule can cause the synthesis of many cAMP molecules that activate PKA, then each PKA can phosphorylate many proteins

speed- large amounts of cAMP can be produced very quickly following ligand binding to the receptor and can quickly diffuse through the cell

Question 7

what are other second messengers?

Answer 7

• activated G-proteins can activate signal transduction through the second messengers IP3 and DAG
• α-subunit activates phospholipase C, that then cleaves the phosphilipid PIP2, producing diacylglycerol (DAG) and inositol triphosphate (IP3)
• IP3 and Ca2+ channels in the ER increase the level of cytosolic Ca2+
• DAG activates protein kinase C (PKC)