Glycogen Metabolism Flashcards
What is glycogen?
A storage polysaccharide made up of glucose units, characterized by extensive branching to store large amounts of glucose.
What enzyme adds glucose-1-phosphate molecules to glycogen?
Glycogen synthase.
What enzyme breaks down glycogen?
Glycogen phosphorylase.
What is glycogenolysis?
The breakdown of glycogen.
What is glycogenesis?
The synthesis of glycogen.
How is glycogenolysis regulated?
It is regulated by phosphorylation of glycogen phosphorylase.
What stimulates glycogen breakdown in the liver during fasting?
Glucagon stimulates the release of glycogen breakdown, increasing blood glucose levels.
What is the role of protein kinase A in glycogen metabolism?
It phosphorylates phosphorylase kinase, activating glycogen phosphorylase and promoting glycogen breakdown.
What happens when glycogen phosphorylase is phosphorylated?
It converts from its low activity form (phosphorylase b) to its high activity form (phosphorylase a).
What is the effect of high glucose concentration on liver glycogen phosphorylase?
Glucose acts as an allosteric inhibitor, preventing glycogen breakdown.
What activates skeletal glycogen phosphorylase?
Allosteric activation occurs in rapidly contracting muscles due to high AMP concentration.
How does calcium affect glycogen breakdown?
Calcium release stimulates muscle contraction and glycogen breakdown.
What is the reciprocal regulation of glycogen metabolism?
Protein kinase A phosphorylates glycogen synthase, converting it to its inactive form, thus inhibiting glycogen synthesis while promoting breakdown.
How is protein phosphatase 1 (PP1) regulated in the fasted state?
PP1 can be downregulated by PKA-dependent phosphorylation mechanisms.
What activates glycogen synthase in the fed state?
Increased blood glucose and insulin release activate glycogen synthase via protein kinase B.
What is the role of insulin in glycogen metabolism?
Insulin activates protein phosphatase 1, promoting glycogen synthesis and inhibiting glycogen breakdown.
Why does a deficiency in muscle glycogen phosphorylase cause mild symptoms?
Muscle glycogen is used for contraction, and deficiency leads to cramps without glucose release into the blood.
What is the consequence of liver glycogen phosphorylase deficiency?
It can lead to severe hypoglycemia and potential coma due to inadequate glucose release.
What are lipids?
More reduced than carbohydrates, generally insoluble in water, and release more energy when oxidized.
What are ketone bodies?
Water-soluble fuel molecules, such as acetoacetate and hydroxybutyrate, derived from acetyl-CoA.
Where do lipids in our body come from?
From diet, storage, utilization as energy, or synthesis in the body.
What is the function of lipoproteins?
They transport lipids, consisting of a neutral core of TAGs and cholesterol esters, surrounded by phospholipids and apolipoproteins.
What is ApoB-100?
A protein part of a lipoprotein involved in cholesterol uptake by receptor-mediated endocytosis.
What are chylomicrons?
A type of lipoprotein mainly consisting of triacylglycerols and proteins like ApoB-48, ApoC-II, and ApoE.
