Download Answer Key for the Supplemental Problem Set #1

BCHM 463
Supplemental Problem Set #1
2005
1. Write the net reaction of glycolysis.
Glucose + 2 ADP + 2 NAD+ + 2 Pi
2 Pyruvate + 2 ATP + 2 NADH + 4 H+ + 2 H2O
2. During glycolysis, how many ADP molecules are converted to ATP. Explain this answer with regard to
your answer to #1.
4 ADP molecules are converted into ATP. There is a net gain of only 2 ATP molecules because 2 are
consumed during the first stage of glycolysis.
3. What are the three metabolically irreversible steps of glycolysis? What general type of reaction is
catalyzed by these enzymes? Why are these reactions irreversible?
Glucose phosphorylation catalyzed by hexokinase; fructose-6-phosphate phosphorylation catalyzed by
phosphofructokinase; and phosphoryl transfer from PEP to ADP catalyzed by pyruvate kinase
All three reactions involve group transfer reactions.
The reactions are irreversible because they have a large negative ∆G. Note: ∆G should not be confused
with ∆G°´. See Table 14.1 for more information.
4. The following is an intermediate formed along the glycolysis pathway. This is produced and consumed
by which enzymes? Provide the net reaction for each catalytic process.
-2
O3PO
OH
HO
OPO3-2
HO
HO
OH
O
phosphoglucose
isomerase
O
-2
OH
OH
O
O3PO
OH
HO
OH OH
G6P
F6P + ATP
phosphofructose
kinase
-2
O3PO
OH
PGI
PFK
Mg2+
OPO3-2
O
OH
HO
OH
F6P
FBP + ADP + H+
5. Name the compounds that serve as phosphoryl group donors in glycolysis and also name the enzymes
that catalyze these phosphoryl transfer steps.
1,3-BPG
ATP
Glucose
F6P
hexokinase
phosphofructose
kinase
1,3-BPG
phosphoglycerate
kinase
ADP
FBP
ATP
PEP
Pi
GAP
G6P
GAPDH
1,3-BPG
PEP
pyruvate
kinase
ADP
ATP
Pyruvate
3PG
BCHM 463
Supplemental Problem Set #1
2005
6. Phosphoglycerate mutase catalyzes the conversion of 3-phosphoglycerate to 2-phosphoglycerate. 2,3Bisphosphoglycerate (2,3-BPG) is formed as an intermediate. Describe the catalytic process that forms
and consumes this intermediate. Does 2,3-BPG serve any physiological function?
3PG
2,3-BPG
2PG
Each step represents group transfer. First, a phosphoryl group is transferred from the enzyme to the
substrate to generate the bisphospho intermediate. This is followed by transfer of the second phosphoryl
group back to the enzyme.
Recall that 2,3-BPG is an allosteric modulator of hemoglobin in erythrocytes although the 2,3-BPG
produced by escape from phosphoglycerate mutase is neglible. This of course means that there is some
other source of 2,3-BPG in erythrocytes.
7. When lactate is converted to pyruvate, which of the following, if any, are true?
a. NAD+ is converted to NADH
b. ADP is converted to ATP
c. NADH is converted to NAD+
d. ATP is converted to ADP
e. FAD is converted to FADH
A is the only answer that is true. Remember that the reaction catalyzed by lactate dehyrogenase is freely
reversible.
8. In Greek mythology, the Three Fates, or Moirae, were the goddesses who controlled the destiny of
everyone from the time they were born to the time they died. Pyruvate also has three fates: fill in the
boxes below to indicate the fate of pyruvate produced during glycolysis.
Glucose
Glycolysis
Pyruvate
anaerobic
conditions
2 EtOH + 2CO2
aerobic
conditions
CO2
anaerobic
conditions
2 Lactate
2 AcetylCoA
citric acid
cycle
4 CO2 + 4 H2O
9. Which enzymes in glycolysis utilize covalent catalysis during conversion of substrate into product?
Write the enzyme names and the net reaction catalyzed by each.
BCHM 463
Supplemental Problem Set #1
2005
GAPDH
1,3-BPG + NADH + H+
GAP + Pi + NAD+
O
Enz
OPO3-2
S
OH
acylenzyme
intermediate
Also, phosphoglycerate mutase see # 6, above
10. Glycolysis is regulated by controlling which enzymes? Identify the mechanisms of control for each.
(e.g. product inhibition or feedback inhibition)
Hexokinase: product inhibition by Glc6P
Posphofructokinase: ATP is an allosteric inhibitor; AMP, ADP, F-2,6-bisP, and other compounds
overcome this inhibition and therefore serve as activators
Pyruvate kinase: product inhibition by ATP (allosteric); FBP acts as an allosteric activator
11. The pentose, xylose, has the same structure as the hexose, glucose, except that it has a hydrogen atom at
C-5 in place of a hydroxymethyl group. However, xylose still stimulates hydrolysis hexokinasedependent hydrolysis of ATP. Why?
Although xylose CANNOT serve as a substrate for hexokinase, it can bind to the enzyme and induce a
conformation similar to that induced by glucose and necessary for enzymatic activity.
.