Glycogen (Deevska) Flashcards
What is the preferred energy source for the brain and RBC’s, and essential for exercising muscles?
Glucose
Glucose is obtained from what 3 things?
Diet, GNG, Glycogen stores
True false: Dietary intake is sporadic, depends on the diet, and is always a reliable source of blood glucose.
False, not always a reliable source
True/False: GNG can sustain synthesis of glucose.
true, but it is slow in response to low blood glucose levels
What does glycogen do?
Mechanism for storing glucose in a rapidly mobilizable form, to maintain blood glucose levels…
2 main stores of glycogen
Skeletal muscle- own use as energy
Liver- maintain blood glucose during early fasting
True/False. Virtually any cell in the human body can store glycogen.
True
Is more glycogen stored in liver or muscle tissue?
Muscle tissue= 400g
Liver= 100g
What also comes along when you store glycogen?
Water makes up of about 5 times the amount of glycogen.
What happens when there is absence of dietary glucose?
Glycogen is broken down to glucose and rapidly released from liver and kidney.
In muscle the same thing happens, but the muscles immediately use it as energy.
Large molecules of glycogen exist as discrete __________ granules (Beta particles).
cytoplasmic
4 steps of glycogen synthesis… a lot here…
- Synthesis of Uridine diphosphate glucose.
-Highly exergonic, traps glucose in the cell, and ensures UDP glucose is sunthesized - Synthesis of a primer to initiate glycogen synthesis.
- Elongation of glycogen chains.
-Glycogen synthase can only elongate primers
-no primers present, protein glycogenin serves as primer and attaches UDP-glucose via alpha (1,4) glycosidic bonds. - Formation of branches
Enzyme: Branching Enzyme
Why are branches on glycogen important?
more branches= more soluble.
Higher surface area= very fast degradation to maintain blood glucose levels. (increase non-reducing ends)
Glycogenolysis 4 steps.
Seperate set of enzymes… not just reversal of Glycogen synthesis.
- Shortening of chains
- Removal of branches
- Conversion of glucose-1-P to glucose-6-P
- Conversion of glucose-6-P to glucose (liver only)
What is the rate limiting step in glycogen degradation?
(step 1) Glycogen to Glucose 1-P via Enzyme: Glycogen phosphorylase
What does Glycogen phosphorylase need as a coenzyme?
Pyridoxal phosphate (PLP) (derived from vitamin B6)
What is the enzyme involved with the removal of branches?
(step 2) Debranching enzyme, which is a single protein with 2 activities.
- 4:4 transferase- breaks alpha1,4 bond and transfers to end of another chain.
- 1:6 glucosidase
What enzyme is involved with conversion of glucose-1-P to glucose-6-P.
(step3) Phosphoglucomutase. Forms Glucose1,6 bisP
What enzyme is involved with dephosphorylation of Glucose-6-P to glucose?
(step4) Glucose 6-phosphatase. (Primarily in the liver)
What does it mean to be reciprocally activated?
Glycogenesis is on then glycogenesis is off… vice versa
What is activated in muscles during exercise?
Glycogenolysis
What is activated immediately after eating in the liver?
Glycogenesis
What begins at rest in the muscle?
Glycogenesis
What happens during fasting in the liver?
Glycogenolysis
What are the two main enzymes of glycogen?
Glycogen synthase
Glycogen phosphorylase
How are Glycogen synthase and glycogen phosphorylase regulated?
Hormonal regulation
Allosteric regulation
Can glycogen synthase and glycogen phosphorylase be active at the same time?
No, reciprocally activated
True/False: Glycogen synthase is active when it is phosphorylated.
True
Explain hormonal regulation.
Glucagon and epinephrine bind leads to cAMP (2nd messenger) activating PKA which activates phosphoylase kinase.
How does glucagon, glucose, and glycogen react to each other?
Glucagon is secreted by low levels of glucose. Glycogen must be broken down to maintain blood glucose levels.
When insulin is secreted insulin binds in ____ and _____ cells.
Liver and muscle
Glucose6-P activates ___________ in liver and muscle.
Glycogen synthase
In muscle, AMP, Ca2+ activates __________.
Glycogen
