Glycogen Flashcards
Glycogen is the storage form of _________ in animals
carbohydrate
where are the primary storage sites of glycogen
liver and skeletal muscle
many glucoses bound together is called a what
polymer
chains of glucose are connected by
alpha 1,4 glycosidic bonds
branch points are formed by
alpha 1,6 glycosidic bonds
branching occurs approximately every ____ glucoses
10
what is the maximal size of a glycogen granule
55,000 glucose molecules
what is proglycogen
it is more sensitive to dietary carbohydrate and synthesized more rapidly following post exercise glycogen depletion
what is macroglycogen
synthesis is slower and more constant. synthesis may last for at least 48 hours post exercise. responsible for carbohydrate loading
can skeletal muscle release glucose
no. it lacks the enzyme needed to release glucose.
can liver release glucose
yes
where is glycogen stored
CYTOSOL
what is the initiation phase of glycogen synthesis
glucose–> G6P–>G1P. G1P is combined with UTP and that makes UDP glucose. Now it is ready to be added onto the chain. To initiate a chain, glycogenin is used by the enzyme glycogen initiator synthase
how many ATP’s are broken down to make G6P
1
___________ is broken down to create UDP glucose
pyrophosphate
how many ATP’s are broken down to attach one glucose
3
what is the very first enzyme glucose meets when it enters a cell?
gluco/hexokinase
what enzyme elongates the chain and what bond does it form
glycogen synthase; alpha 1,4
what enzyme branches the chain and what bond does it form
glucosyl 4:6 transferase; alpha 1,6
Glycogen is broken down into glucose by what enzyme
glycogen phosphorylase
G1P–>G6P
phosphoglucomutase
the breakdown of glycogen will continue until when
until there are four glucose molecules left prior to a branch point, phosphorylase is no longer effective at breaking down glycogen
what are the two enzymes required to break down the glycogen branches
glucosyl (4:4) transferase (removes the outer three glucose molecules) and amylo alpha (1,6) glucosidase (removes the last glucose of the branch. Then glycogen phosphorylase can begin again until it gets 4 away from the next branch point
Glycogen is regulated by what two enzymes
glycogen synthase and glycogen phosphorylase
what stimulates glycogen phosphorylase
low ATP, high AMP/ADP, low glucose, glucagon (liver), muscle contraction (calcium)
what stimulates glycogen synthase
high energy charge, lots of glucose, insulin, low glycogen levels
glucagon shuts down glycogen _______ and activates glycogen_______
synthesis; breakdown
what is the most potent stimulator of glycogen
glycogen levels within muscle
what effects does exercise have on glycogen
intense exercise burns muscle and liver glycogen. increases GLUT4 translocation, increases GLUT4 transcription-translation, stimulates glycogen synthesis after exercise and increases insulin sensitivity after the exercise
what happens to glycogen after intense exercise
glycogen synthesis has an initial high rate. maximal activity during the first 30 minutes, and rapid decline to about one fifth by 60 minutes. reduced to about one ninth by 120 minutes. Two reasons: 1. increased glycose uptake (GLUT4’s) 2. increased glycogen enzyme activity (glycogen synthase)
explain the rapid phase of glycogen synthesis
30-60 min post-exercise. Insulin independent. occurs when muscle glycogen levels are relatively low and carbohydrate is provided immediately after exercise
explain the slow phase of glycogen synthesis
follows the rapid phase (several hours). Insulin dependent. much slower rate of glycogen synthesis. must have carbs available and insulin
explain the insulin independent phase
also called rapid phase. less than 3-6 hours post-exercise. AMPK pathway stimulated. PI3K pathway is temporarily inhibited
explain the insulin dependent phase
also called slow phase. 3-6 to 48 hours post-exercise.
If high glycemic carbohydrates are consumed after exercise what happens
the resultant hyperinsulinemia leads to only a modest increase in glycogen synthase activity
consumption of carbohydrate after exercise _______ glycogen synthesis
increases
ingestion of protein/amino acids in combination with moderate carbohydrate intake post exercise leads to what
higher muscle glycogen synthesis rates compared to the same amount of carbohydrate alone
what type of protein impacts muscle glycogen levels the most
whey protein hydrolysates
intense workout compared to moderate burns more fat or carbs?
carbs
explain the glycemic index
increase in blood glucose level over the base-line level during a 2 hour period following the consumption of a defined amount of carbohydrate compared with the same amount of carbohydrate in a reference food (white bread or glucose)
explain the glycemic load
glycemic index times the grams of carbs in a serving of the food. Considers both quantity and quality of carb in the meal. the higher the GL, the greater the expected elevation in blood glucose and in the insulinogenic effect of the food. This is what you don’t want happening before bed or a workout. By the time you go to bed your blood glucose is crashing. bigger the meal the harder the crash. smaller meals before bed will help blood glucose slowly return instead of crashing
what happens to insulin during exercise
within minutes of the start of exercise, insulin levels rapidly fall and reach the same low values, regardless of the GI of the pre-exercise meal
Glucokinase has a ______ km than hexokinase
higher
what is the main endogenous source of glucose
the liver
when blood glucose is in the normal range what effect will insulin have on the liver
insulin will not cause the liver to take in glucose
what role does fructose play in glycogen synthesis
no benefit for muscle glycogen synthesis
low doses of fructose _______ liver glycogen synthesis
increase
Why are high levels of fructose not good
liver has a high uptake (50% on first pass) increased fat, lactate and glycerol formation. HFCS and sucrose are not that different
what are the enzymes for glycogen synthesis
hexo/glucokinase, phosphoglucomutase, UDP glucose pyrophosphorylase, pyrophosphatase, glycogen initiator synthase, glycogen synthase, glucosyl 4:6 transferase
what are the enzymes for glycogen breakdown
glycogen phosphorylase, phosphoglucomutase, glucosyl (4:4) transferase, amylo alpha (1,6) glucosidase
what conditions will you experience glycogen synthesis
high blood glucose, insulin, fructose*, low glycogen content, high energy charge, ATP
what conditions will you experience glycogen breakdown
low blood glucose, glucagon, low energy charge, ADP/AMP, calcium (muscle contraction)
