E2 Glycogenesis Flashcards
Define glycogenesis.
glycogen synthesis
The first step in glycogenesis is to phosphorylate glucose. What enzyme will facilitate this rxn (glucose —> G-6-P)?
hexokinase (m)/ glucokinase (L)
What will inhibit hexo/glucokinase?
the product
T/F. Step one of glycogenesis utilizes ATP.
true
The second rxn of glycogenesis, G-6-P —> G-1-P, is facilitated by what enzyme?
phosphoglucomutase
T/F. Phosphoglucomutase is also used in glycogenesis.
true
The third step of glycogenesis requires two enzymes. What are the enzymes?
- G-1-P + UTP + H2O —> UDP glucose +PPi
- PPi —> Pi + Pi
- UDP- glucose pyrophosphorylase
2. pyrophosphorylase
What is the name of activated glucose?
UDP-glucose
T/F. G-1-P + UTP + H2O to UDP-glucose + PPi is an irreversible rxn.
false
What will make G-1-P + UTP + H2O to UDP-glucose + PPi is an irreversible rxn?
hydrolyzing pyrophosphate quickly, which drives rxn toward producing UDP-glucose
When pyrophosphate is hydrolyzed, why does it make G-1-P + UTP + H2O to UDP-glucose + PPi is an irreversible rxn?
because it is liberating energy and lots of energy is needed to reverse the rxn
The fourth step of glycogenesis adds glucose to glycogen an forms alpha (1-4) bonds via what enzyme?
glycogen synthase
T/F. During the formation of alpha (1-4) bonds, glucose is added to reducing ends of glycogen.
false; non-reducing ends
In order to form alpha (1-4) bonds, we need glucose. Where does this glucose come from?
activated glucose (UDP-glucose)
The fifth step of glycogenesis deals with branching via what enzyme?
glycosyl (4:6) transferase
What are the two actions of glycosyl (4:6) transferase?
- break alpha (1-4) bonds
2. form alpha (1-6) bonds
What is the integral protein that will catalyze the formation of the “primer” of a glycogen granule?
glycogenin
Glycogenin is required to initiate a new glycogen granule, but what does glycogenin require?
tyrosine
Within a glycogen granule, each chain has how many glucose residues?
12-14
When glycosyl (4:6) transferase breaks alpha (1-4) bonds, a segment is transferred to a hydroxyl group on carbon #__ of a chain to form a branch.
6
What enzyme is the key regulatory enzyme of glycogenesis?
Glycogen synthase
How many forms of glycogen synthase are there? Name them.
2
- glycogen synthase a
- glycogen synthase b
What form of glycogen synthase is the active, non-phosphorylated form?
glycogen synthase a
T/F. Glycogen synthase b is active and phosphorylated.
False; b= inactive and phosphorylated
If glycogen synthase a is active, what state is it in?
R state
If glycogen synthase b is inactive, what state is it in?
T state (less active)
What are the three types of regulation for glycogenesis?
- allosteric regulation
- covalent modification
- reciprocal regulation
Allosteric regulation of glycogenesis is activated by what enzyme?
glucose-6-phosphate
What tissue types will you find allosteric regulation of glycogenesis?
Liver and Muscle
T/F. Allosteric regulation is in a Fed state.
True
What type of glycogenesis regulation prevents glycogenolysis from occurring at the same time as glycogenesis?
covalent modification
What two hormones are associated with glycogenesis regulation?
glucagon and epinephrine
T/F. Reciprocal regulation of glycogenesis will stimulate the CAMP cascade.
False; covalent modification
What type of glycogenesis regulation states that the same conditions that stimulate glycogen breakdown will inhibit glycogen synthesis?
reciprocal regulation
What two hormones stimulate glycogen breakdown?
epinephrine and glucagon
What will stimulate protein phosphatase 1 (PP1)?
insulin and exercise
What is the function of protein phosphatase 1 (PP1)?
dephosphorylates the enzymes
When protein phosphatase 1 (PP1) dephosphorylates the enzymes, what enzymes become inactive? Active?
Inactive- glycogen phosphorylase and glycogen phosphorylase kinase
Active- glycogen synthase
In the liver, PP1 is removing phosphate groups from glycogen synthase converting it to what form?
a form- active
What hormone will cause PP1 to dephosphorylate the glycogen synthase converting it to the more active (a) form?
insulin
When glycogen synthase is converted to the more active a form in liver, what process is stimulated?
glycogen synthesis (glycogenesis)
If glucose binds to the active site on phosphorylase a, it will shift from _____ state to ______ state.
R state —> T State
T/F. If glucose binds to the active site of phosphorylase a, glycogenesis in the liver is inhibited.
False; inhibits glycogen degradation
In the muscle, what role does insulin have when it comes to glycogenesis?
when carbohydrate is available, we can stimulate glycogen synthesis to ensure we have fuel stored.
T/F. It is not important to replenish our glycogen because there should be enough stored.
False
What is the most potent stimulator of glycogen synthase in skeletal muscle?
low glycogen levels, like after exercise
Low glycogen levels, like after exercise, is the most potent stimulator of what enzyme in skeletal muscle?
glycogen synthase
What happens to glycogen synthase during low glycogen levels?
glycogen synthase, that is usually bound to the glycogen granule, is released when glycogen concentration falls
After intense exercise, when is glycogen synthesis at the highest rate?
initially; first 30 minutes
T/F. After intense exercise, glycogen synthesis rapidly declines to about 1/5th and then 1/9 by 60 minutes and 120 minutes respectively.
true
What are the two reasons why glycogen synthesis rapidly declines with time?
- increased glucose uptake (GLUT4)
2. increased enzyme activity (glycogen synthase)
T/F. In muscle, the rapid and slow phase are both insulin dependent.
False; rapid-independent
When does the rapid phase of glycogenesis occur in the muscle?
30-60 minutes after exercise
What two factors will stimulate the rapid phase of glycogenesis in the muscle?
- muscle glycogen levels are low
2. carb is provided immediately after exercise
When does the slow phase of glycogenesis occur in the muscle?
after the rapid phase
How long does the slow phase of glycogenesis last in the muscle?
can last a few hours
T/F. The slow phase of glycogenesis only needs carbohydrates or insulin response in order to be stimulated.
false; must have carbohydrates available and insulin response
T/F. Muscle glycogen synthesis rates may be 45% lower when carbohydrate ingestion post-exercise is delayed by 2 hours compared with immediate post-exercise consumption.
true
Why do muscle glycogen synthesis rates lower when carbohydrate ingestion post-exercise is delayed by 2 hours compared with immediate post-exercise consumption?.
the number of glucose transporters associated with the sarcolemma returns to pre-exercise concentration
What can be added to the diet to moderate carb intake?
protein/amino acids
What function will adding protein/amino acids to moderate carb intake have on muscle?
higher muscle glycogen synthesis rates than carbohydrate alone
T/F. If you have very high carbohydrate concentration and consumed protein, this will significantly increase glycogen synthesis rates.
False; if carbohydrate is very high, the protein doesn’t matter
During carb loading, depleting glycogen reduces the power output of the muscle to ___%.
50%
What is the purpose of carb loading?
super compensation: store glucose above normal storage amount
What factors will stimulate glycogen phosphorylase to convert glycogen to G-1-P?
- low energy charge (Low ATP; High ADP/AMP)
- low levels of glucose
- epinephrine
- glucagon
- calcium
What factors will stimulate glycogen synthase to convert G-1-P to glycogen?
- high energy charge (High ATP)
- high levels of glucose
- insulin
- low glycogen levels
