Carbohydrate metabolism, glycogen and gluconeogenesis

Question 1

what is glycogenesis

Answer 1

synthesis of glycogen from glucose

Question 2

what is glycogenolysis

Answer 2

breakdown of glycogen to form glucose

Question 3

what is glycogen

Answer 3

main storage form of glucose in liver and muscle cell

Question 4

liver glycogen

Answer 4

broken down between meals and released to maintain blood glucose levels for red blood ells and brain

Question 5

muscle glycogen

Answer 5

not available for maintenance of blood glucose levels

provides energy during bursts of physical activity

Question 6

what is the primary source of glucose overnight when hepatic glycogen is depleted

Answer 6

gluconeogenesis

Question 7

how is glycogen joined together

Answer 7

it is a polymer consisting of glucose molecules joined by alpha 1-4 glycosidic bonds

Question 8

what is the name of the primer in glycogen

Answer 8

glycogenin

Question 9

what is the name of the enzyme that moves the phosphate from carbon 6 to carbon 1

Answer 9

phosphoglucomutase

Question 10

what is UDP glucose

Answer 10

it is an activated intermediate (commonly used in biosynthetic pathways

Question 11

formation of udp glucose

Answer 11

UTP+ Glucose-1-P —> UDP-glucose + pyrophosphate(PPi)

Question 12

what is the hydrolysis reaction of pyrophosphate

Answer 12

PPi + H2O —> 2Pi

Question 13

what does glycogen synthase do

Answer 13

-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

Question 14

what is the branching enzyme and what does it do

Answer 14

transglycosylase, introduces alpha 1-6 glycosidic branches into glycogen (approximately every 10 glucose residues)

Question 15

when does glycogenesis occur

Answer 15

during and immediately after meals, when blood glucose is increased

Question 16

what are the hormones that control the rate of glycogenesis

Answer 16

insulin and glucagon

Question 17

what does hyperglycemia mean

Answer 17

where the blood sugar level increases

Question 18

what is hypoglycemia

Answer 18

where the blood sugar level drops too low

Question 19

when we are hyperglycemic what hormone is released and what is the effect

Answer 19

insulin is released from the pancreatic beta cells and this results in the activation of glycogenesis (storage of glucose)

Question 20

when we are hypoglycemic what hormone is released and what is the effect

Answer 20

glucagon is released from the pancreatic alpha cells and there is the inactivation of glycogenesis

Question 21

what is glycogenolysis catalyzed by

Answer 21

glycogen phosphorylase

Question 22

equation of glycogenolysis

Answer 22

[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

Question 23

can glucose-6-phosphate be de-phosphorylated in the liver

Answer 23

yes and the resulting glucose is released into the bloodstream

Question 24

can glucose-6-phosphate be de-phosphorylated in skeletal muscle

Answer 24

no, but instead it is used to provide energy via glycolysis and the TCA cycle

Question 25

what is the glycogen breakdown summary?

Answer 25

glycogen —> glucose-1-phosphate(via glycogen phosphorylase) —> glucose-6-phosphate(via phosphoglucomutase)

Question 26

what is gluconeogenesis

Answer 26

it is the synthesis of glucose within the body from non-carbohydrate precursors

Question 27

during prolonged periods of starvation new glucose has to be synthesized, what are other ways

Answer 27

-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

Question 28

where would the energy come from when starved

Answer 28

from oxidation of fatty acids released from adipose tissue

Question 29

what is gluconeogenesis the reverse of

Answer 29

glycolysis

Question 30

where does gluconeogenesis take place

Answer 30

liver and small amounts in the kidneys

Question 31

how many unique enzymes does gluconeogenesis require

Answer 31

4 liver enzymes

Question 32

what is a anaplerotic reaction

Answer 32

important for accepting acetyl groups from fat breakdown

Question 33

what is the cori cycle

Answer 33

-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