glycogenesis and glycogenolysis Flashcards
(53 cards)
when is glycogen formed in the liver?
after a meal
between meals, what does the glycogen from the liver do?
provides an immediate source of glucose for maintenance of of blood glucose levels or during vigorous exercise when the use of blood glucose increases by the muscles
what does glycogen do in skeletal muscles and other tissues?
skeletal
- important fuel source when energy demands are high
other cell types
- small stores of glycogen also serve as an emergency fuel source for generating ATP when oxygen supply or blood flow is restricted
how much glycogen is found in the liver and muscles?
100g and 400g, respectively
what does insulin insensitive mean?
if a tissue is insulin insensitive, it means they do not require insulin for glucose uptake
can an insulin insensitive tissue be effected by insulin? if so, how?
yes. glucose transport in some insulin insensitive cells increases in the presence of insulin
which cells are insulin sensitive? insulin insensitive?
sensitive
- most tissues (adipose, muscle)
insensitive
- erythrocytes
- leukocytes
- lens of eye
- cornea
- LIVER
- brain
is the liver insulin sensitive or insensitive?
the liver is insulin insensitive
what happens to insulin levels after a carbohydrate meal?
after a carbohydrate meal:
- blood glucose rises
- rise in blood glucose causes a RISE in insulin secretion
what happens as insulin binds to cell membrane receptors?
insulin binds to cell membrane receptors and GLUT 4 from intracellular vesicles move to the cell membrane
what GLUT moves to the cell membrane after a meal and why?
- GLUT 4 moves to cell membrane
- this allows more glucose to enter the cell and as a result, blood glucose levels drop
failure of glucose transport is a major characteristic of what?
diabetes
what is a direct result of insulin-stimulated translocation of GLUT-4?
this will result in activation of protein kinase B (PKB)
pkb phosphorylates proteins involved in GLUT-4 translocation
between meals, what happens to insulin levels?
decline
what does muscle contraction require?
glucose uptake for the generation of energy
what stimulates glucose uptake by the muscles between meals?
increase in AMP levels and the subsequent (after) activation of AMP-stimulated protein kinase (AMPK)
what does AMPK activation do in muscle cells?
AMPK activation promotes the translocation of GLUT-4 transporters to muscle membrane
what 2 things will promote translocation of GLUT 4 transporters?
- AMPK activation (a result of increased AMP levels)
- insulin binding to cell membranes
where is AMP generated?
in the adenylate kinase reaction
when does glycogenesis begin (what event)?
the transfer of the terminal phosphate group from ATP to the hydroxyl group in C-6 of glucose to form glucose-6-phosphate
what reaction is common to all pathways that utilize glucose?
what pathways utilize glucose this way?
the transfer of a phosphate to glucose to form glucose-6-phosphate
- glycogenolysis
- glycolysis
- pentose phosphate pathway
what is significant about the phosphorylation of glucose?
glucose-6-P cannot pass through the cell membrane to the extracellular side, keeping it within the cell and committed to further metabolism
- cannot pass back because it is not a substrate for the glucose transporters
describe hexokinase
- km to glucose (and what this means)
- type of enzyme
- what tissues
- inhibited or not by product (G6P)
hexokinase:
- 0.2 mM Km, meaning it has a high affinity for glucose
- constitutive enzyme (produced by cell under all conditions)
- in tissues in general
- INHIBITED by G6P
describe glucokinase
- km to glucose (and what this means)
- type of enzyme
- what tissues
- inhibited or not by product (G6P)
glucokinase
- 10 mM Km, meaning it has a low affinity for glucose
- induced enzyme (stimulated by an inducer)
- in the liver and pancreatic beta cells
- NOT inhibited by G6P
