M3b L28

Question 1

Describe the basic elements of a signal transduction pathway

Answer 1

ligand-receptor-intracellular messaging-outcome
end result is phosphorylation or dephosphorylation of proteins

Question 2

Distinguish between cell surface receptors and nuclear receptors

Answer 2

cell surface: the receptor doesn’t cross the membrane, hormone binding site is located extracellularly, The signaling molecule could be an ion, a hormone, light, voltage, a neurotransmitter or a growth factor.
nuclear receptors: they bind to ligands (steroid hormones) that can cross the membrane directly, bind to receptor in cytosol

Question 3

Outline the types of cell-cell communication mediated by hormones

Answer 3

Endocrine hormones circulate in the blood and affect distance cells, peptides
Paracrine signals are directed at nearby cells, local hormones
Autocrine signals are directed at the same cell that produced them cytokines

Question 4

Outline two common on-off switches for signaling pathways

Answer 4

1. G-proteins: guanine nucleotide exchange and hydrolysis, switching mechanism GDP/GTP GTP binds, GDP gets kicked out after its turned on a phosphate leaves, and exchange, irreversible
2. Protein phosphorylation is a reversible modification of proteins, input signal is received, kinase activates ATP –> ADP, turns on, has phosphate, output signal, phosphatase inactivates, Phosphate leaves, turned off

Question 5

Describe G-protein signaling and cellular response(s) in the context of glucagon signaling in liver and adipose tissue

Answer 5

happens at the same time
adipose tissue: Protein Kinase A activates Hormone Sensitive Lipase (HSL)/Triacylglycerol Lipase. This enzyme starts triacyl-glyceride breakdown by hydrolysis to give a free fatty acid and a diacylglyceride Other lipases hydrolyze the di- and mono- acyl-glycerides to free fatty acids and glycerol

liver: Glucagon binds the cell surface receptor, initiating GDP/GTP nucleotide exchange and activation of adenylate cyclase. The production of cAMP starts a “kinase cascade” by activating Protein Kinase A. Protein Kinase A phosphorylates glycogen phosphorylase kinase, rendering it active. The now active phosphorylase kinase will phosphorylate glycogen phosphorylase, rendering it active, it breaks down glycogen to glucose-1-phosphate

Question 6

Describe tyrosine kinase signaling and cellular response(s) in the context of insulin signaling in liver, muscle and adipose tissue

Answer 6

Process called autophosphorylation one enzyme will phosphorylate another enzyme as part of its control mechanism, activation or inhibition, process of autophosphorylation is a protein adding a phosphate group onto itself
Increase in
glucose uptake in muscle and liver
glycogen synthesis in muscle and liver
glycolysis in liver and adipose tissue to acetyl-CoA