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INTRODUCTORY BIOCHEMISTRY
BIOL0280
Second Midterm Examination
April 4, 2013
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DO NOT WRITE YOUR NAME ON THIS EXAM
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you with your exam after grading it. Please work independently. Read each question carefully
before answering. Unless otherwise indicated, there is only one correct answer for each
multiple-choice question. Points are indicated by the question within brackets []. There are no
calculators or other electronic devices needed or allowed on this exam. All hats must be
removed during the exam. Exams will be photocopied before being returned.
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Exam total __________/ 100
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1. [4 points] Indicate whether the following statements are true or false by circling T or F.
T/F
The cofactor thiamine pyrophosphate is involved in reactions in which bonds to
phosphate groups are synthesized or cleaved.
T/F
NADPH is a cofactor of pyruvate dehydrogenase.
T/F
Pyruvate dehydrogenase converts pyruvate to acetyl-CoA.
T/F
The first step of the citric acid cycle, the synthesis of citrate, is highly endergonic.
Circle the correct answer.
2. [2 points] Which molecules are shown in this figure from the citric acid cycle?
3. [2 points] Briefly describe how the cofactor FAD shown in the figure above is regenerated.
4. [2 points] Which of the following intermediates of the citric acid cycle is prochiral?
A)
B)
C)
D)
E)
Citrate
Isocitrate
Malate
Oxaloacetate
Succinate
Circle the correct answer.
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5. [2 points] Anaplerotic reactions
A)
B)
C)
D)
E)
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.
produce oxaloacetate and malate.
produce biotin needed by pyruvate carboxylase.
recycle pantothenate used to make CoA.
produce glucose from acetyl-CoA.
all of the above
Circle the correct answer.
6. [2 points] During seed germination, the glyoxylate pathway is important to plants because it
enables them to:
A)
B)
C)
D)
E)
carry out the net synthesis of acetyl-CoA from malate.
carry out the net synthesis of glucose from acetyl-CoA.
further metabolize isocitrate formed from the aconitase reaction.
obtain glyoxylate for cholesterol biosynthesis.
obtain glyoxylate for pyrimidine synthesis.
Circle the correct answer.
7. [4 points] Briefly describe how the oxidation of NADH in the electron transport chain is
connected to ATP synthesis.
8. [5 points] Indicate whether the following statements are true or false by circling T or F.
T/F
T/F
T/F
T/F
T/F
Complex I participates in both the electron transport chain and the citric acid
cycle.
Heme is a prosthetic group of cytochromes.
Only one out of the 9 total α- and β-subunits of ATP synthase contains bound
ADP at any given time.
The Q cycle serves to transfer electrons from cytochrome c to molecular oxygen.
The isolated F1 complex of ATP synthase catalyzes ATP hydrolysis.
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9. [2 points] Which statement is not true about the transport of ATP across the mitochondrial
membrane on its way to the cytosol?
A) It is accomplished by adenine nucleotide translocase.
B) ATP is complexed with Mg2+ for electroneutral passive antiport.
C) The same translocase that transports ATP also transports ADP in the opposite direction.
D) The transport causes the loss of a net charge of -1 in the matrix.
E) ATP is transported across the inner mitochondrial membrane.
Circle the correct answer
10. [4 points] Briefly describe what is shown in the figure to the right.
11. [7 points] Indicate the location each of the following components in the photosynthetic
electron transport pathway of plants by placing the numbers corresponding to the
components in the spaces provided.
H2O → _____ → _____→ _____→ _____→ _____→ _____→ _____→ NADP+
1. Ferredoxin
2. Oxygen-evolving complex
3. Plastocyanin
4. Plastoquinone
5. Cytochrome b6f complex
6. Reaction center of Photosystem I
7. Reaction center of Photosystem II
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12. [2 points] The three subcellular organelles involved in the phosphoglycolate salvage
pathway are:
A)
B)
C)
D)
E)
endoplasmic reticulum, chloroplast, and mitochondrion.
nucleus, endoplasmic reticulum, and chloroplast.
golgi apparatus, chloroplast, and mitochondrion.
mitochondrion, peroxisome, and chloroplast.
peroxisome, endoplasmic reticulum, and chloroplast.
Circle the correct answer.
13. [5 points] Complete the following description of photosynthesis:
In photosynthesis, the _____________________________________ of light is converted
to ______________________________________, which is used to drive the
______________________ of __________________ (with electrons derived from H2O)
and the formation of the triosephosphate
___________________________________________.
14. [2 points] An intermediate found in gluconeogenesis and not in glycolysis is ___
A) 2-phosphoglycerate
B) phosphoenolpyruvate
C) fructose-1,6-bisphosphate
D) oxaloacetate
E) 3-phosphoglycerate
Circle the correct answer
15. [2 points] Which molecule is shown in the figure to the right?
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16. [2 points] Which enzyme produces the molecule shown in the previous question?
17. [4 points] Indicate whether the following statements are true or false by circling T or F.
T/F
T/F
T/F
T/F
In glycogenesis, sugar phosphates are substrates for polymerization.
Glycogen synthase forms (α1→4) linkages.
Glycogenin remains covalently bound to the glycogen molecule.
Glycogen and starch are degraded by glycogen hydrolase.
18. [4 points] Briefly describe how fatty acids are activated for catabolic oxidation.
19. [4 points] The list below includes metabolic reactions and processes for the catabolism of
fatty acids. Number the items in the order in which they occur in an organism beginning
with fatty acids in the cytoplasm.
Start: Fatty acid in cytoplasm
_____
transport of fatty acid into mitochondrion
_____
thiolytic cleavage
_____
formation of acyl-carnitine
_____
dehydrogenation to a trans-Δ2-enoyl-CoA
_____
dehydrogenation to a β-Ketoacyl-CoA
_____
hydration of double bond
_____
linkage of fatty acid to CoA
_____
transfer of fatty acid from carnitine to CoA
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20. [2 points] The major site of formation of acetoacetate from fatty acids is the:
A)
B)
C)
D)
E)
adipose tissue.
liver.
intestinal mucosa.
kidney.
muscle.
Circle the correct answer.
21. [2 points] What type of bond best describes the linkage between acyl carrier protein (ACP)
and fatty acids in fatty acid biosynthesis?
A) phosphoanhydride
B) thioester
C) peptide
D) amide
E) Schiff base
Circle the correct answer
22. [4 points] What are ‘essential fatty acids’ chemically and why are they called ‘essential’?
23. [3 points] Complete the following statements:
Triacylglycerols and glycerophospholipids are synthesized from the common precursor
____________________________. Sphingolipids are not built onto glycerol, instead they are
derived from _________________________ and ________________________________.
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24. [2 points] The coenzyme involved in a transaminase reaction is:
A)
B)
C)
D)
E)
biotin phosphate.
lipoic acid.
nicotinamide adenine dinucleotide phosphate (NADP+).
pyridoxal phosphate (PLP).
thiamine pyrophosphate (TPP).
Circle the correct answer.
25. [2 points] The carbon in urea originates from ______.
A) Ornithine
B) aspartate
C) bicarbonate
D) ATP
Circle the correct answer
26. [2 points] Which of these directly donates a nitrogen atom for the formation of urea during
the urea cycle?
A)
B)
C)
D)
E)
Adenine
Aspartate
Creatine
Glutamate
Ornithine
Circle the correct answer.
27. [4 points] In the biosynthesis of amino acids, list amino acids that are derived from
α-ketoglutarate: ______________________________________________________________
or from
3-phosphoglycerate: __________________________________________________________
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28. [4 points] Briefly describe the biochemical function of the enzyme dinitrogenase and list
substrate(s), product(s) and other relevant enzyme(s).
29. [2 points] The Cori cycle is:
A) the conversion of lactate to pyruvate in skeletal muscle to drive glycogen synthesis.
B) the interconversion between glycogen and glucose l-phosphate.
C) the production of lactate from glucose in peripheral tissues with the resynthesis of
glucose from lactate in liver.
D) the synthesis of alanine from pyruvate in skeletal muscle and the synthesis of pyruvate
from alanine in liver.
E) the synthesis of urea in liver and degradation of urea to carbon dioxide and ammonia
by bacteria in the gut.
Circle the correct answer.
30. [4 points] Indicate whether the following statements are true or false by circling T or F.
T/F
T/F
T/F
T/F
Phosphocarnitine serves as ‘stored ATP’ to regenerate ATP during bursts of heavy
activity.
The brain requires glucose as preferred energy source but can use ketone bodies
and fatty acids when glucose is unavailable.
Glucagon and insulin act in opposition, in some cases on the same target enzyme.
Epinephrine regulates glucagon and insulin secretion.
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31. [2 points] An elevated insulin level in the blood:
A)
B)
C)
D)
E)
inhibits glucose uptake by the liver.
inhibits glycogen synthesis in the liver and muscle.
results from a below-normal blood glucose level.
stimulates glycogen breakdown in the liver.
stimulates synthesis of fatty acids and triacylglycerols in the liver.
Circle the correct answer.
32. [2 points] What type of signal transduction is shown in the figure?
33. [4 points] Briefly describe key elements of steroid hormone signal transduction in the cell.
Where does the receptor bind the ligand, what is the biochemical activity of the activated
receptor, and what is the biochemical result of receptor activation?