Lecture 18 Flashcards
T or F, glycerol is released during triacylglycerol hydrolysis in adipose tissue
True, and can enter glycolysis as DHAP
T or F, galactose and fructose are good energy sources yet lack dedicated pathways for processing
True
Which enzymes are involved in the metabolism of fructose into the glycolytic pathway?
- fructokinase
- fructokinase phosphate aldolase
- triose kinase
- triose phosphate isomerase
Briefly describe the fructose1-phosphate pathway.
- phosphorylation of fructose to yield F 1-P
- splitting of F 1-P into glyceraldehyde and DHAP via aldol cleavage
- phosphorylation of glyceraldehyde to GAP
GAP –> glycolysis
Which enzyme is involved in the formation of galactose to glycolytic intermediates?
galactokinase
– there’s a release of ADP and H+
True or false
Increasing the pH of the environment will increase galactose metabolism
true. H+ is product of one of the steps so removing it would shift it towards products
Which of the following does not occur as a result of low lactase levels?
A) build up of lactic acid
B) buildup of methane and hydrogen gas
C) formation of ethanol
D) osmotic change that results in drawing water into the intestine
C
Why are some people “lactose intolerant”
– deficiency in lactase enzyme prevents conversion of lactose to galactose and glucose
– lactose build-up allows microorganisms in the colon to ferment it to lactic acid, with methane and hydrogen gas as byproducts. Result is flatulence
– in addition, lactate produced by microorganisms draws water into intestine, causing diarrhea
– if that weren’t enough, severe gas and diarrhea hinder uptake of fats, proteins, and other nutrients
T or F, in animal metabolism, glucose is derived mainly from dietary polysaccharides, starch from plants and glycogen from meat as well as the body’s own glycogen stores
True
true or false
alpha 14 linkages give glycogen a helical structure whereas b 1 4 linkages of cellulose give it a stacked configuration
true
True or false
2/3 of glucose exists in its beta pyranose formation
true; 66% where as 33% of it exists in alpha pyranose and less than 1% exists in open-chain form
When does branching occur in glycogen?
– it occurs every 10 - 12 residues
True or false
non reducing ends are a result of branching in glycogen that allow for quick degradation when needed
True
T or F, when energy demands increase suddenly, glycogen is a readily mobilized source of glucose
true
T or F, controlled utilization of glycogen is what keeps blood-sugar levels constant between meals
True; glycogen supplies glucose to brain, which uses glucose as primary fuel
T or F, branching producing a compact structure for cellular storage and also creates the presence of many non-reducing ends allows for quick degradation when energy is needed
True
What are the 4 enzymatic activities allow glycogen to be processed into useable glucose 6-phosphate (feeds into glycolytic pathway):
– 1 activity cleaves glycogen to form glucose 1-phosphate
– 2 activities remodel glycogen so it can be cleaved again
– 1 activity coverts glucose 1-P to glucose 6-P
Which of the following is NOT a typical step in glycogen breakdown?
A) phosphorylase of glycogen to produce a glucose 1 phosphate
B) hydrolysis of glycogen to form glucose via glycogen phosphorylase
C) cleavage of alpha 1 6 bonds by alpha 1 6 glucosidase
D) transfer of 3 glucose subunits to non-reducing ends via transferase
B
True or false
hexokinase is responsible for phosphorylating the final glucose liberated from a branch point
True
True or false
glycogen phosphorylase is not able to function within 2 residues of a branch
False, 4 –> cleavage of alpha 1,4 linkages by glycogen phosphorylase does not occur within 4 residues of the branch site
True or false
transferase is responsible for transferring one glucose unit at a time from the branch to a non reducing end
false, 3 units at a time
T or F, phosphorolytic cleavage of glycogen is energetically advantageous because the released sugar is already phosphorylated
True; no need to burn ATP
What enzyme is responsible for the removal of the final glucose unit from the branch
– alpha 1-6 glucosidase
– as final glucose unit is removed from branch, free glucose is then phosphorylated by hexokinase to be used in glucose
– now the glycogen chain can be completely broken into monomers by phosphorylase
Which of the following is true of alpha 1 6 glucosidase?
A) it adds a phosphoryl group to the glucose residue
B) it is capable of hydrolyzing a 6 long glucose residue chain
C) It removes a glucose unit and phosphorylates it.
D) none of the above
D; it removes final glucose unit from branch and none of these describe that
True or false
phosphoglucomutase contains a modified phenylalanine to mutate G1P to G6P
false. modified serine residude; transfers phosphoryl group C-1 to C-6
True or false
glycogen breakdown occurs only in muscles and the liver
True
true or false
G6Pase is not present in the liver
false, it is not present in muscles
What is the general structure of glycogen phosphorylase?
a multisubunit enzyme that has catalytic sites and a site that contains a serine residue.
– there is an a and b form and each form can assume 2 activity states R (relaxed) and T (tense)
Which states are glycogen phosphoylase A and B more likely to exist in at equilibrium?
– a is found mostly in the active, R state while b is the opposite, it exists mostly in the active T state
T or F, a and b interconvert by virtue of serine phosphorylation ( a is the phosphorylated form, b is not)
True
T or F, phosphorylase is mostly in b form in muscle
true; it is regulated allosterically by the cell’s energy charge
How is phoshporylase b regulated allosterically?
– by cell’s energy change
– AMP binds nucleotide binding site in a manner that favors R state
– ATP binds nucleotide binding site in a manner that favors T state
G 6-P favors T state, example of feedback inhibition
T or F; muscle phosphorylase a is not subject to the same type of allosteric regulation as muscle phosphorylase b
True
Which of the following is true about GP A and B?
A) GP A contains a phosphoserine residue
B) GP B has a covered active site in the phosphorylated state
C) conversion of B to A involved the use of 1 ATP molecule
D)
Phosphoserine residues stabilize the tense state
A
What is the difference in phosphorylase b in resting and active muscle?
– resting = phosphorylase b is in predominant form; AMP is low, ATP is high and thus the enzyme is inhibited (T state)
– active = AMP rises, ATP decreases, and phosphorylase b is activated to R state
T or F, hormone signaling (adrenaline) can induce phosphorylation of b, converting some of it to even more active a form
True
Which of following is TRUE concerning the energy level of the body when it comes to GP activity in the non-liver isoform
A) in a state where ATP levels is high, one would expect the stabilization of the R state
B) one would expect high levels of G6P to stabilize the T state
C) glucose would tend to stabilize the T state of the enzyme
D) extraneous exercise would tend to stabilize the T state of GP
B; because remember feedback inhibition
true or false
High ratio of AMP:ATP would result in the stabilization of the R state of GP B
true
true or false
hydrolysis of ATP to the allosteric site results in switch from the R to T state
– false. ATP hydrolysis results in changing of isoform state due to changing serine residue nature.
– Binding of ATP to allosteric sites not hydrolysis, switches between R/T
T or F, in the liver, phosphorylase is primarily active in a form
Ture; 98% identical to muscle form
T or F, liver phosphorylase is not subject to allosteric control by the cell’s energy charge
True; liver phosphorylase is regulated by glucose
Describe the regulation of phosphorylase by glucose in the liver.
– binding of glucose to liver phosphorylase causes a R to T transition and thereby inhibits the enzyme
– Why? Don’t need to breakdown glycogen if glucose levels are high
T or F, the 2% difference between muscle and liver phosphorylase matters
True; liver and muscle phosphorylase are 98% identical at the aa level yet are subject to very different modes of allosteric regulation
