Download Midterm Exam Advanced Biochemistry II (Answer) 1. At equilibrium

Midterm Exam
Advanced Biochemistry II
(Answer)
1. At equilibrium in solution, D-glucose consists of a mixture of its anomers. Which
statement most accurately describes the solution?
A) The solution consists of approximately equal amounts of the - and -anomers.
B) The straight-chain form is present in high concentration.
C) The -anomer is more stable and is slightly preferred over the -anomer.
D) The -anomer predominates over the -anomer by a ratio of approximately 2:1.
E) None of the above.
2.
A)
B)
C)
D)
E)
Which of the following sugars is not a reducing sugar?
glucose
ribose
sucrose
starch
galactose
3.
A)
B)
C)
D)
E)
How many stereoisomers are possible for an aldopentose such as ribose?
2
4
8
16
32
4.
A)
B)
C)
D)
E)
How many stereoisomers are possible for a ketopentose such as ribulose?
2
4
8
16
32
5.
A)
B)
C)
D)
E)
Which of the structures is a glucopyranose?
A
B
C
D
None of the above
6.
A)
B)
C)
D)
E)
Which structure is a ketose?
A
B
C
D
None of the above
7.
A)
B)
C)
D)
E)
Which structures are glucoses?
A
A, B
A, C
A, B, C
None of the above
8.
A)
B)
C)
D)
E)
Which is deoxyribose?
A
B
C
D
None of the above
9. Which of the following segments of the integral membrane protein glycophorin most
likely contains the membrane-spanning sequence:
A) LSTTEVAMHTTTSSSVSKSY
B) ISSQTNDTHKRDTYAATPRA
C) HEVSEISVRTVYPPEEETGE
D) PEITLIIFGVMAGVIGTILL
E) ISYGIRRLIKKSPSDVKPLP
10.
A)
B)
C)
D)
E)
Which would be most likely to be found in the cell membranes of arctic mammals?
very high concentrations of cholesterol
polyunsaturated lipids
saturated lipids
trans-fats
elevated concentrations of hemoglobin
11.
A)
B)
C)
D)
E)
The mannose-6-phosphate marker is used to direct proteins to the _______________.
lysosome
rough endoplasmic reticulum
outer leaflet of the cellular membrane
nucleus
cytoplasm
12. Glycosphingolipids with several attached carbohydrates (including at least one sialic
acid) are called:
A) lipid rafts
B) ceramides
C) sphingiosides
D) gangliosides
E) proteoglycans
13. What is true about the (Na+–K+)–ATPase transporter?
A) three potassium ions bind to the cytostolic face of the transporter in the E1 state
B) GTP binds to it and is hydrolyzed to form GDP and a high energy phosphorylated
glutamyl residue
C) formation of the high-energy phosphorylated glutamyl residue triggers a conformational
shift from the E1 form to the E2 form
D) bound Na+ ions are released from the E2 state to the extracellular medium, and two
potassium ions are bound to the dephosphorylated E2
E) phosphate hydrolysis of the E2 state releases potassium ions to the cytosol and results in
rearrangement to the E1 state
14. Ouabain inhibits the (Na+–K+)–ATPase pump, resulting in
A) K+ ions moving into the cell along a concentration gradient
B) K+ ions bringing water molecules into the cell in order to maintain an osmotic balance
C) extra K+ ions and water in cells causing them to swell and lyse
D) an increase the strength of heart muscle contractions when small amounts of Ouabain
are used
E) all of the above
15. Fermentation to Produce Soy Sauce Soy sauce is prepared by fermenting a salted
mixture of soybeans and wheat with several microorganisms, including yeast, over a period
of 8 to 12 months. The resulting sauce (after solids are removed) is rich in lactate and
ethanol. How are these two compounds produced? To prevent the soy sauce from having a
strong vinegar taste (vinegar is dilute acetic acid), oxygen must be kept out of the
fermentation tank. Why?
Answer Soybeans and wheat contain starch, a polymer of glucose, which is broken down to
glucose by the microorganisms. The glucose is then degraded to pyruvate via glycolysis.
Because the process is carried out in the absence of oxygen (i.e., it is a fermentation),
pyruvate is reduced to lactic acid and ethanol. If oxygen were present, pyruvate would be
oxidized to acetyl-CoA and then to CO2 and H2O. Some of the acetyl-CoA, however, would
also be hydrolyzed to acetic acid (vinegar) in the presence of oxygen.
16. Explain the regulatory role of Phosphofructokinase (PFK) in glycolysis
17. Glycolysis Shortcut Suppose you discovered a mutant yeast whose glycolytic pathway
was shorter because of the presence of a new enzyme catalyzing the reaction
Would shortening the glycolytic pathway in this way benefit the cell? Explain.
Answer Under anaerobic conditions, the phosphoglycerate kinase and pyruvate kinase
reactions are essential. The shortcut in the mutant yeast would bypass the formation of an
acyl phosphate by glyceraldehyde 3-phosphate dehydrogenase and therefore would not allow
the formation of 1,3-bisphosphoglycerate. Without the formation of a substrate for 3phosphoglycerate kinase, no ATP would be formed. Under anaerobic conditions, the net
reaction for glycolysis normally produces 2 ATP per glucose. In the mutant yeast, net
production of ATP would be zero and growth could not occur. Under aerobic conditions,
however, because the majority of ATP formation occurs via oxidative phosphorylation, the
mutation would have no observable effect.
18. Role of Lactate Dehydrogenase During strenuous activity, the demand for ATP in
muscle tissue is vastly increased. In rabbit leg muscle or turkey flight muscle, the ATP is
produced almost exclusively by lactic acid fermentation. ATP is formed in the payoff phase
of glycolysis by two reactions, promoted by phosphoglycerate kinase and pyruvate kinase.
Suppose skeletal muscle were devoid of lactate dehydrogenase. Could it carry out strenuous
physical activity; that is, could it generate ATP at a high rate by glycolysis? Explain.
Answer The key point here is that NAD_ must be regenerated from NADH in order for
glycolysis to continue. Some tissues, such as skeletal muscle, obtain almost all their ATP
through the glycolytic pathway and are capable of short-term exercise only (see Box 14–2).
In order to generate ATP at a high rate, the NADH formed during glycolysis must be
oxidized. In the absence of significant amounts of O2 in the tissues, lactate dehydrogenase
converts pyruvate and NADH to lactate and NAD_. In the absence of this enzyme, NAD_
could not be regenerated and glycolytic production of ATP would stop—and as a
consequence, muscle activity could not be maintained.