Topic Homeostasis & Cell Signalling Essay - Main Points!

Describe the mechanism of action of glucagon in the homeostatic control of human blood glucose

Main points
Key idea:	Role of glucagon in maintaining homeostatic level of glucose at 100mg/100ml of blood
· Glucagon secreted when blood glucose drops below 100mg/100ml of bl · Ref to α cells (of Islets of Langerhans) detect this change & secrete glucagon directly into bl · Bl transport peptide hormone to target cells (e.g. liver cells)
Key idea:	Glucagon signalling in target cells
· Peptide hormone binds to G protein-linked receptor + activates G protein · Ref to a GTP displaces previously bound GDP in protein · Active G protein moves freely along membr + binds to & activates adenylyl cyclase · Ref to enz catalysing conversion of ATP to cyclic adenosine monophosphate (cyclic AMP or cAMP), a second messenger · cAMP then activates a protein kinase which triggers next step in pathway leading to cell’s response
Key idea:	Cellular responses
· Cellular responses include (i) activation of glycogen phosphorylase for breakdown of glycogen (i.e. glycogenolysis), increase in availability of glucose for cellular resp (ii) Enz (e.g. glycogen synthase) also inhibited (iii) Conversion of aa & fats to glucose (i.e. gluconeogenesis). · Taken together, all these cellular responses restore normal bl glucose conc level
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Insulin and glucagon are peptide hormones. They are unable to pass through the cell memrbane via simple diffusion. They bind to specific cell surface receptors and initiate signal transduction pathways that result in specific cellular responses that will collectively restore the homeostatic level of blood glucose in the body.