Biochemistry 2280A Study Guide - Midterm Guide: Ketone Bodies, Blood Sugar, Triglyceride
30 Apr 2018
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Biochemistry 2280 – Midterm
Big Picture: Energy Metabolism
Explain the effects of insulin and glucagon in the main pathways of
energy metabolism
Fed state
• e’e eaten, blood glucose is high, pancreas secretes insulin
• stimulates uptake of glucose by many tissues
• increases glycolysis to make ATP because we can
• when we have lots of ATP, we don't have to do that anymore (cycle is inhibited)
• this turns on other pathways (storing waste; glycogen or triacylglycerols)
• taking intermediates and making other biosynthetic molecules with them
• some glucose-6-phosphate is diverted through the PPP to make NADPH and ribose-5-
phosphate
Unfed state
• glucose is low, pancreas secretes glucagon
• inhibits glycolysis
• glycogen is the first energy source to take out of storage; easy to break down
• liver releases glucose from glycogen (keeps the brain happy for a while)
• then muscle cells break down their own glycogen if they need more (and fatty acids)
• eventually (after about 16 to 24 hours), the body breaks down glucose from amino
acids with gluconeogenesis
• adipocytes release fatty acids from storage (but the brain doesn’t use those;
muscle/liver do)
• fatty acids make ketone bodies but that takes a while (not main source of energy for
brain)
• biosynthesis is not favoured in this state
Describe the metabolic responses to prolonged fasting
- gluconeogenesis cannot continue indefinitely; nitrogen becomes depleted
- the body then needs proteins to survive
- release of fatty acids and glycerols from triacylglycerols continues and the sustained level of
fatty acid in the blood leads to increased ketone body production in the liver
- the brain adapts, and the ketone bodies become its main source of energy
- muscle tissue continues to use fatty acids
- in general, all metabolism slows as the body tries to conserve energy
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