Carbohydrate metabolism, glycogen and gluconeogenesis Flashcards
what is glycogenesis
synthesis of glycogen from glucose
what is glycogenolysis
breakdown of glycogen to form glucose
what is glycogen
main storage form of glucose in liver and muscle cell
liver glycogen
broken down between meals and released to maintain blood glucose levels for red blood ells and brain
muscle glycogen
not available for maintenance of blood glucose levels
provides energy during bursts of physical activity
what is the primary source of glucose overnight when hepatic glycogen is depleted
gluconeogenesis
how is glycogen joined together
it is a polymer consisting of glucose molecules joined by alpha 1-4 glycosidic bonds
what is the name of the primer in glycogen
glycogenin
what is the name of the enzyme that moves the phosphate from carbon 6 to carbon 1
phosphoglucomutase
what is UDP glucose
it is an activated intermediate (commonly used in biosynthetic pathways
formation of udp glucose
UTP+ Glucose-1-P —> UDP-glucose + pyrophosphate(PPi)
what is the hydrolysis reaction of pyrophosphate
PPi + H2O —> 2Pi
what does glycogen synthase do
-synthesizes glycogen from UDP-glucose (a rate-limiting enzyme of glucogenesis)
-adds one glucose molecule to glycogen at a time
-can only extend the chains of glycogen
what is the branching enzyme and what does it do
transglycosylase, introduces alpha 1-6 glycosidic branches into glycogen (approximately every 10 glucose residues)
when does glycogenesis occur
during and immediately after meals, when blood glucose is increased
what are the hormones that control the rate of glycogenesis
insulin and glucagon
what does hyperglycemia mean
where the blood sugar level increases
what is hypoglycemia
where the blood sugar level drops too low
when we are hyperglycemic what hormone is released and what is the effect
insulin is released from the pancreatic beta cells and this results in the activation of glycogenesis (storage of glucose)
when we are hypoglycemic what hormone is released and what is the effect
glucagon is released from the pancreatic alpha cells and there is the inactivation of glycogenesis
what is glycogenolysis catalyzed by
glycogen phosphorylase
equation of glycogenolysis
[glucose] + (Pi) —> glucose-1-phosphate + [glucose]n-1
-this is the rate-limiting step of glycogenolysis
-one glucose molecule is cleaved of the ends at a time
-glucose-1-phosphate is then converted to glucose-6-phosphate
can glucose-6-phosphate be de-phosphorylated in the liver
yes and the resulting glucose is released into the bloodstream
can glucose-6-phosphate be de-phosphorylated in skeletal muscle
no, but instead it is used to provide energy via glycolysis and the TCA cycle
what is the glycogen breakdown summary?
glycogen —> glucose-1-phosphate(via glycogen phosphorylase) —> glucose-6-phosphate(via phosphoglucomutase)
what is gluconeogenesis
it is the synthesis of glucose within the body from non-carbohydrate precursors
during prolonged periods of starvation new glucose has to be synthesized, what are other ways
-lactate: synthesized by skeletal muscle under anaerobic conditions
-amino acids: derived from muscle protein by proteolysis
-glycerol: derived from triglycerides by lipolysis in adipose tissue
where would the energy come from when starved
from oxidation of fatty acids released from adipose tissue
what is gluconeogenesis the reverse of
glycolysis
where does gluconeogenesis take place
liver and small amounts in the kidneys
how many unique enzymes does gluconeogenesis require
4 liver enzymes
what is a anaplerotic reaction
important for accepting acetyl groups from fat breakdown
what is the cori cycle
-blood transports lactate to the liver
-the liver converts lactate back to glucose
-glucose is released into the bloodstream
-buys time and shifts the metabolic burden from the muscle to other organs
