Basics of carbohydrate utilisation during exercise

Question 1

carbohydrates as a source of energy
- why does glucose have high chemical energy
- basically how does glucose then resynthesise ATP

Answer 1

• glucose has 23 C-H bonds
• Glucose is broken down into smaller carbon subunits. Electrons are passed onto electron carriers which are used to resynthesise ATP

Question 2

basic carb recpa
- what do you call different numbers of bonded carb monomers
- how are monomers joined
- what different bonds do amylopectin and glycogen have
- features that make them digestable and optimal for energy provision

Answer 2

• Monosaccharides (1), disaccharides (2), oligosaccharides (2-10) and polysaccharides (>10) carbohydrate units
• α(1-4) – glycosidic bonds
• α(1-6) – glycosidic bonds repeat every 20-30 residues for starch and every 8-12 residues for glycogen
• Compact, hydrophilic molecules with high surface area due to branches

Question 3

digestion of carbs-
- where does it occur
- enzymes
- how does absorption work

Answer 3

• mouth (saliva), small intestine, villi of small intestine
• amylase to oligosaccharides in the small intestine, and then to disaccharides on the villi, specific enzymes (lactase, maltase, sucrase) break di into mono
• absorbed into the cytosol of enterocytes and transported into capillaries that empty into venous blood and the portal vein that supplies the liver

Question 4

glycogen content of liver and muscle-
- what is the volume of glycogen in liver and muscle
- more glycogen in liver or muscle?
- where is glycogen in muscles
- how is muscle glucose increased during exercise

Answer 4

• liver (3-7%) and muscle (1-1.5%)
• muscle as there’s more muscle than liver
• stored in granules in the sarcomere, with enzymes for its breakdown and storage, between thick and thin filaments of the sarcomere and near the mitochondria.
  -breakdown of glycogen in liver and transported in blood to muscle

Question 5

synthesis of glycogen
- type of reaction
- process
- enzymes used

Answer 5

• Anabolic, condensation
• Uridine Triphosphate (UTP) reacts with glucose to provide energy to build the glycogen chain
• glycogenin, glycogen synthase & branching enzyme

Question 6

breakdown of glycogen
- type of reaction
- process
- enzymes used

Answer 6

• Catabolic, hydrolysis
• phosphorylation reaction - A phosphate group is added to glucose to release it from the glycogen chain
• glycogen phosphorylase & debranching enzyme

Question 7

glycogen breakdown during exercise
- what happens to rate of glycogen breakdown when muscles contract
- what enzyme is responsible for this
- what increases the activity of this enzyme and why(4)
- which 2 are direct and which 2 are indirect

Answer 7

• increases rapidly in muscles and liver
• glycogen phosphorylase
• 1.↑ Pi - GP substrate 2.↑ AMP/ATP ratio AMP binds to an enzyme that increases GP activity 3.↑ Adrenaline - binds to adrenaline receptor, causes conformational change activating cyclic AMP to bind to GP 4.↑ Ca2+ - accumulating calcium increases activity
• 1 and 2 direct, 3 and 4 indirect

Question 8

impact of Exercise on Glycogen synthase

Answer 8

when exercise starts glycogen synthase activity is inhibited (allowing glycogen breakdown to occur). Prolonged periods of exercise may activate GS to maintain energy balance. GS can be rapidly activated after exercise.