Glycogen Metabolism Flashcards
This is the storage form of carbohydrates in animals.
Glycogen
What are the primary storage sites of glycogen?
Liver and skeletal muscle
This type of glycogen is more sensitive to dietary carbohydrates and is synthesized more rapidly following post-exercise glycogen depletion.
Proglycogen
This type of glycogen has a much slower and constant synthesis. It is responsible for carbohydrate loading (supercompensation).
Macroglycogen
How many grams of glycogen can skeletal muscle hold? Can it release glucose?
400 grams and skeletal muscle cannot release glucose
How many grams of glycogen can the liver hold? Can it release glucose?
100 grams and the liver can release glucose
Where would you store your glycogen?
Cytosol
What is the general mechanism for glycogen synthesis?
- Phosphorylate glucose
- Make UDP-glucose
- Initation
- Elongation of the chain
- Branching
This is a protein that starts the glycogen chain with the amino acid tyrosine.
Glycogenin
What is the enzyme that starts the glycogen chain?
Glycogen initiator synthase
When you are resynthesizing glycogen you are using what?
ATP
How many ATPs are broken down to attach each glucose for glycogen synthesis?
3
What is the enzyme, type of bonds created, and location of elongation of a glycogen chain?
Glycogen synthase adds alpha (1–>4) bonds in the cytosol
What is the enzyme and type of bonds created in the branching phase of glycogen synthesis?
Glucosyl 4:6 transferase adds alpha (1–>6) bonds
What enzyme degrades glycogen?
Glycogen phosphorylase
After glycogen has been degraded into glucose 1P what enzyme converts it into glucose 6P?
Phosphoglucomutase
When is glycogen phosphorylase no longer effective at breaking down glycogen?
When there are four glucose molecules left prior to a branch point
When glycogen phosphorylase is no longer effective, two new enzymes are required to continue glycogen degradation. What are they?
- Glucosyl (4:4) transferase: removes the outer three glucose molecules
- Amylo-alpha-(1,6)-glucosidase: removes the last glucose of the branch
What are the main regulating enzymes of glycogen synthesis?
Glycogen synthase (sitmulates) and glycogen phosphorylase (inhibits)
What does exercise do to GLUT4, glycogen synthesis, and insulin sensitivity?
GLUT4: increased translocation and increased amount of transporters
Glycogen synthesis: stimulated after exercise
Insulin sensitivity: increased after exercise
This phase of glycogen synthesis occurs 30-60 minutes after exercise, is insulin independent, and occurs when muscle glycogen levels are relatively low and carbohydrates are provided immediately after exercise.
Rapid phase
This phase of glycogen synthesis occurs several hours after exercise, is insulin dependent, is a much slower rate of glycogen synthesis, and must have carbohydrates and insulin available.
Slow phase
What are the two phases of increased glucose uptake?
Insulin-independent: <3-6 hours post exercise, AMPK pathway stimulated, P13K pathway is temporarily inhibited.
Insulin-dependent: 3-6 to 48 hours post-exercise
Does consumption of carbohydrates after exercise increase glycogen synthesis?
Yes
Is glycogen storage higher in trained athletes than the normal individual?
Yes
This is the increased in blood glucose level over the base-line level during a 2 hour period following the consumption of a defined amount of carbohydrate compared with the same amount of carbohydrate in a reference food.
Glycemic index
This term is used to describe the glycemic index times the grams of carbohydrate in a serving of the food. It considers both the quantity and the quality of the carbohydrate in a meal.
Glycemic load
The ____ the glycemic load, the ____ the expected elevation in blood glucose and in the insulinogenic effect of the food.
Higher; greater
What factors are involved with the synthesis of glycogen?
- High blood glucose
- Insulin
- Fructose (impacts liver not muscle)
- Low glycogen content
- High Energy Charge
- ATP
What factors are involved with the breakdown of glycogen?
- Low Blood Glucose (impacts liver not muscle)
- Glucagon (impacts liver not muscle)
- Low Energy Charge
- ADP, AMP
- Calcium (muscle contraction)
