QUESTION 16 Use the figure below to tie all the topics from the unit together. W

Question

QUESTION 16 Use the figure below to tie all the topics from the unit together. Write a paragraph describing what's happening in the figure, putting the relevant lectures in paraenthesis where appropriate. Reference at least 6 lectures. Ex: (Glut2 is a protein (lecture 6) build by macromolecular synthesis) o insulin oglucose GLUT4 nsulin receptors active nactive signal transduction gene expression & growth regulation glucose utilization Muscle cell glycogen /lipid/protein synthesis 2004 BETA CELL BIOLOGY CONSORTIUM

Explanation / Answer

The figure shows the effect of insulin on muscle cell glucose metabolism.

When the blood glucose levels increase, insulin is secreted from pancreatic beta cells. Insulins acts to lower the blood concentration by activating insulin-sensitive glucose transporters (GLUT-4 ) in various cell types including muscle. Binding of insulin to its receptor on muscle cells triggers the fusion of vesicles containing GLUT-4 transporter to the plasma membrane and this transporter embeds in the plasma membrane where it can carry its function of glucose uptake.

Insulin also acts on the target cell by triggering them to make glycogen (storage form of glucose), lipids and protein synthesis. Lipid synthesis will also increase because acteyl CoA concentration increases as a result of increased rate of glucose oxidation to acetyl CoA. Acetyl CoA is a precursor of fatty acid synthesis.

Insulin also triggers protein synthesis via signal transduction through PI3K mTOR signalling pathway. Insulin binds to its receptor and triggers its tyrosine kinase acitivity in the intracellular domain. Activated phosphorylated receptor then triggers a cascade of phosphorylation and activation events downstream of it. Ultimately S6K (ribosomal protein) is activated and 4EBP1 ( eIF4E-binding proteins ) is inactivated leading to increased rate of protein synthesis.

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