Flashcards in Part 2 - lecture 2 - Quiz Deck (29):
What is glucose stored as?
What are the processes of building up and breaking glycogen down?
Glycogenolysis - breaking down
Glycogenesis - build up
Where is glycogen found?
Mostly in liver and muscle - higher percentage stored in liver but more muscle in our body so total is more in muscle
What is the purpose of glycogen in liver?
Maintains circulating blood glucose and varies in response to diet - shares with other tissues through GLUT2
What is the purpose of glycogen in muscles?
Used as a reserve for ATP synthesis - does not form free glucose to maintain circulating levels
Where are enzymes of glycogen digestion located?
In the cytosol
When do glycogen granules in liver show absence in fasted animals?
What does glycogen produce in red and white muscle cells?
Red = goes to CO2 and H20
White = goes to lactate
Do white or red muscle cells have more capacity for glycolysis and glycogenolysis?
What is the strucutre of glycogen?
Linear amylose chain with branched amylopectin at every 4th residue (less frequent further out)
What are the chain terminals in glycogen used for?
Accept glucose during glycogenesis or sites of degradation during glycogenolysis
Why do we not store glucose as fat?
Glycogen can be utilized in absence of oxygen and converts to glucose and mobilizes faster than fat
Why do we not store glucose as glucose?
Glucose is osmotically active and would bring in water and cause cell to burst - glycogen does not
How does glycogen degradation occur?
Glycogen phosphorylase cleaves the alpha 1,4 linkages between two glucose units by adding a phosphate group at terminal non-reducing ends to form glucose 1-P --> mutase make G6P and in liver G6P becomes glucose from G6 phosphatase or in liver tissue G6P is used in glycolysis to get lactate in white muscle or CO2 in red
How is glycogen completely degraded?
Debranching enzyme uses transferase to remove 3 glucosyl residues and transfer to free end and single residue left is broken by glucosidase to give free glucose
What is Pompe disease?
Type II glycogen storage disease - lysosomal storage disease where alpha-1,4-glucosidase found in lysosomes is deficient -- leads to accumulation of glycogen and causes cardiomegaly
What is Cori's disease?
Type III - debranching deficiency -- can lead to accumulation of glycogen --
can lead to mild fasting hypoglycemia
What is Hers disease?
Type VI - Liver phosphorylase deficiency - can lead to mild fasting hypoglycemia
What is McArdle syndrome?
Type V - skeletal muscle phosphorylase deficiency - causes muscle cramping -- glycogen stores are not available to exercising muscle - releases other enzymes like CK, aldolase and myoglobin
What is von Gierke syndrome?
Type I - Translocase or G6phosphatase deficiency in liver and kidney which causes glucose to not be produced leading to fasting hypoglycemia (severe) lactic acidosis (from gluconeogenesis being inhibited), hyperlipidemia, hyperuricemia (more purines formed - cause gout), renomegaly, hepatomegaly (enlarged kidney and liver) - must be fed with continuous carbohydrates
How is glycogen synthesized?
It utilizes glycogenin to link glucose to one of it's tyr residues - glucokinase/hexokinase with ATP forms G6P + ADP --> then phsphoglucomutase makes G1P --> G1Puridyltansferase makes UDP-glucose + PPi -- added by glycogenin -- glycogen synthase transfers activated UDP-glucose to form new alpha1,4 linkage -- when at least 11 residues branching enzyme moves 7 residues to form alpha 1,6
What is glycogenin?
A self-glucosylating enzyme that uses UDP glucose to link glucose to one of its own Tyr residue - serves as a primer
What regulates glycogen phosphorylase (from glycogen to glucose)?
G6P and ATP inhibit in liver and muscle -- have enough energy
Glucose inhibits in liver
AMP and Ca activate in muscle -- need more energy
What does glucagon in liver do to glycogen production?
Glucagon acts as phosphorylating kinase to activate cAMP to activate glycogen phosphorylase kinase to activate glycogen phosphorylase which degrades glycogen -- insulin would activate synthesis because it acts as a dephosphorylator
What activates glycogen synthase (G1P to glycogen)?
G6P - signaling excess glucose is available
What is the major function of glucagon in liver?
To mobilize liver glycogen during periods of low food intake - also inhibits glycolysis at PFK1 and pyruvate kinase
What has an effect similar to glucagon?
What does calcium do to glycogen in muscle?
Activates phosphorylase kinase which leads to activation of glycogen phosphorylase to degrade glycogen