Download Objectives 7

1.
- Energy is stored as glycogen (carbohydrates), protein (amino acids) or triacylglyercols (fatty
acids)
- The four circulating fuels are glucose (most important), lactate, free fatty acids, and ketone
bodies; these provide fuel in response to specific physiological conditions
- In fed and early starvation states (< 1 week) states the brain relies on glucose, whereas in
prolonged starvation ketone bodies become the fuel for the brain
- Most energy in the body is produced by complete oxidation of acetyl CoA leading to ATP
production
2. After a meal, a large portion of dietary glucose bypasses the liver, and promotes release of
insulin from beta-cells from the pancreas
- insulin accelerates storage and metabolism of glucose in liver, muscle, and adipose
- surplus fuel is converted to glycogen and fat under + influence of insulin
- kinases in liver phosphorylate sugars (glucose, fructose, and galactose) to trap them in the cell
- In the liver, glucose is first stored as glycogen and excess is metabolized to fatty acids (stored
as TAGs)
- excess carbohydrates are stored as TAGs in adipose tissue (fat)
- In well-fed state, liver utilizes exogenous glucose (no de novo synthesis)
- RBCs metabolize glucose anaerobically for energy (no mitochondria)
- muscle stores some glucose as glycogen or may metabolize glucose anaerobically or
aerobically, depending on the capillary and mitochondrial content associated with a particular
muscle
- uptake of glucose in the liver is max. active even when insulin is not present; liver transporter
functions independent of insulin preventing hyperglycemia
3. Look at table on 7-5
- uptake of glucose by adipose and muscle cells is insulin-regulated to ensure uptake occurs
only when glucose is abundant
- glucose transport proteins stored in the cell are moved to the plasma membrane after insulin
binds to its cell surface receptor
- uptake of glucose by brain depends on glucose availability to ensure adequate fuel for brain
function
- glucose transporters characterized by insulin-dependent or insulin-independent and by the
specific transport protein involved
4. Sources of blood glucose include the diet (exogenous glucose) in absorptive phase, liver
glycogen (endogenous via glycogenolysis) in postabsorptive phase (4-20h after food intake),
and de novo glucose synthesis in the liver (gluconeogenesis) from amino acids in early and
prolonged starvation
- amino acids and lactic acid are key substrates for gluconeogenesis
- use of glucose in the body diminishes as food deprivation progresses
- reduced use is first apparent in liver, muscle and adipose tissue, followed later by diminished
metabolism in the brain during prolonged starvation
5. Major fuel of the brain
Well-fed: Glucose
Post-absorptive: Glucose
Early gluconeogenic starvation: Glucose
Prolonged gluconeogenic starvation: Ketone bodies
6.
- the energy from hydrolysis of the terminal ATP phosphoanhydride bond drives energyrequiring reactions of biological processes
- release of these phosphates from ATP and other high-energy phosphate compounds constitutes
the high-energy phosphate transfer potential
- oxidation of fuels provides energy for the phosphorylation of ADP  ATP (oxidative
phosphorylation)
- compounds having higher energy phosphate bonds, than exists between the beta and gamma
phosphates of ATP, can phosphorylate ADP without consumption of oxygen (substrate-level
phosphorylation)