L21- Glycogen Flashcards Preview

Biochemistry > L21- Glycogen > Flashcards

Flashcards in L21- Glycogen Deck (22):

How is glycogen stored?

In cytosolic granules in muscle and liver cells of vertebrates


What is glycogenolysis?

Degradation of glycogen


What does glycogen breakdown yield?

Glucose 1-phosphate (G1P)
Which can be converted to glucose 6-phosphate (G6p)
for metabolism via glycolysis


What does glycogen phosphorylase (GP) do?

catalyzes the sequential removal of glucose residues.
Breaking down glycogen. It stops 4 residues away from the branch point and cuts it off.
Results in a "limit dextrin" (like a y shape)which is degraded by a glycogen-debranching enzyme.
Then GP can break it down again to glucose molecules.


How is cellular glucose converted to G6P?

By glucokinase in the liver cells


What is required to incorporate one G6p into glycogen?

Three seperate steps
Glycogen synthase is the major regulatory step


Where is insulin produced and what does it stimulate?

Produced by beta cells of the pancreas
Increase rate of glucose transport into muscle, adipose tissue
stimulates glycogen synthesis in the liver


Where is glucagon made and what does it stimulate?

Produced by the alpha cells of the pancreas in response to low blood glucose
Stimulates glycogen degradation


What does adrenaline do?

Released by adrenal medulla when energy is requires
stimulates breakdown of glycogen to G1p


What is gluconeogenesis?

Liver and kidney make glucose from monocarbohydrate precursors such as lactate and alanine


Which steps in glycolysis require seperate enzymes for gluconeogenesis?

Only the 3 irreversible steps of glycolysis


What is the overall equation for gluconeogenisis

2 pyruvate + 2nadh+4atp+2gtp+6H20+2H+

goes to

glucose + 2nad+ + 4adp + 2gdp + 6Pi


Compare the energy used in gluconeogenesis to the energy generates in glycolysis?

Costs more to generate glucose than energy generated in glycolysis. because neither process is 100% efficient.


What does pyruvate carboxylase do?

pyruvate---> phosphoenolpyruvate
1st step of gluconeogenesis


What is pyruvate carboxylase (PK) activated by?

allosterically by acetyl coA
accumulation of acetylcoA from fatty acid oxidation signals abundant energy supply so starts gluconeogenesis


What are the precursors for gluconeogenesis?

Any metabolite that can be converted to pyruvate or oxolacetate. Major precursors:
1. lactate
2. most amino acids (especially alanine)
3. glycerol (from triglycerol hydrolysis)


What is the Cori cycle?

Interaction of glycolysis and gluconeogenesis.
Glucose makes lactate when muscle is anaerobic. liver uses lactate for gluconeogenesis. can regenrate glucose from this. Principal supply of energy for gluconeogenesis= fatty acid breakdown


What does glutamate dehydrogenase do in plants?

Incorporates ammonia into glutamate.
alpha-ketoglutarate +NH4---> glutamate +H20


How else is ammonia assimilated (not by glutamate dehydrogenase)?

Via glutamine synthetase.
Glutamate +NH3--> Glutamine

uses ATP


What is the transamination reaction in amino acid biosynthesis?

The amino group of glutamate is transferred to alpha keto acids generating alpha amino acids.


In amino acid catabolism what does transamination generate?

Glutamate or aspartate


What does the urea cycle do?

Converts ammonia into urea.
Waste nitorgen removed as it's toxic
(birds, reptiles - uric acid instead)