Biol 200, Autumn 2014
Exam 1, Key
N
This exam is worth 90 points. Pages 2-5 have questions. Page 1 is for your reference only.
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Page #
2
3
12
4
6
5
Exam
Total
(out of 90)
5
12
The number next to each
intermediate represents the
total # of C-C and C-H bonds
in that molecule.
5
12
5
4
12
9
9
5
5
5
6
6
8
6
6
1
7
7
total
Biol 200, Autumn 2014
Exam 1, Key
N
1. (10 pts) For each choice below, write an "X" in the blank for the stronger interaction or bond in each
pair. 2 points each
a. ___X___ a C-G base pair
vs.
an A-U base pair ______
b. ___X___ disulfide bond in protein structure
vs.
ionic bond in protein structure ______
c. ___X___ bond formed by a ribozyme's catalysis vs. a bond in protein 2° structure ______
d. ______ interaction between sigma and RNA polymerase
vs. phosphodiester bonds ___X___
e. ____ interaction between phospholipid tails vs. ester linkage between glycerol and fatty acid __X__
2. (10 pts) The diagram to the right shows the Na+/K+
ATPase. Cells normally have high K+ and low Na+
concentrations in their cytoplasm, whereas outside the cell
Na+ is high and K+ is low.
(2 pts each)
a. When the Na+/K+ ATPase is working normally, it moves
K+ which way? (Circle ONE best answer)
- cytoplasm  outside
- outside  cytoplasm
outside cell
-R
P
cytoplasm
Conformation A
Conformation B
b. Which ion binds more tightly to conformation A? __K+____
c. Which conformation is more likely to bind ATP? ___B___
d. Which of the R-groups to the right is most likely
found where you see the "R" in conformation A?
(Circle the BEST answer)
e. Which of the following is responsible for the change from conformation A to B?
A. Addition of the phosphate group to an amino acid on the Na+/K+ ATPase
B. Energy released as heat when ATP is broken apart
C. Binding of Na+ ions to ATP
D. Breaking of the bond between the Na+/K+ ATPase and the phosphate group
3. (6 pts) Imagine you have a lipid bilayer made primarily of phospholipids with unsaturated tails.
(2 points each)
a. Which of the following molecules will be permeable through this bilayer? (Circle ALL correct
answers)
- ATP
- H2 O
- H+
- CO2
- RNA polymerase
b. Would permeability increase or decrease if you changed to saturated tails? decrease
c. Would permeability increase or decrease if you lowered the temperature? decrease
2
Biol 200, Autumn 2014
Exam 1, Key
N
4. (6 pts) Imagine a cell in which there is a mutation in the gene for the amino-acyl tRNA synthetase
that binds to the tRNAs with the 3'UCU5' and 3'UCC5' anticodons. The mutant amino-acyl tRNA
synthetase enzyme still binds to the same tRNAs, but it binds to the amino acid asparagine (Asn)
instead of the normal amino acid. There are no other mutations in the cell. Which of the following
will be true? Put an "X" in the blank for all correct answers. (The codon table is printed below.)
(+3 points each correct, -2 for "Arg" will never be included, -3 for any other incorrect answer)
______ Most proteins will be a bit shorter than in normal cells
______ The amino acid "Arg" will sometimes be added where "Asn" normally would be in proteins
______ The amino acid "Asn" will sometimes be added where "Ser" normally would be in proteins
__X___ There will be more tRNAs carrying "Asn" in the mutant cell compared to normal cells
______ There will be more tRNAs with the 3'UCU5' anticodon in the mutant cell
______ The amino acid "Arg" will never be included in any proteins in the mutant cell
______ There will be more tRNAs carrying "Ser" in the mutant cell compared to normal cells
___X__ The amino acid "Asn" will sometimes be added where "Arg" normally would be in proteins
5. (12 pts) Below is the sequence of a complete mRNA transcribed from a gene in bacteria.
5' CUCGGAAGGUUACCUAAUGCUCGGGAUGUCCUAGGAACCCAUAAUAAU 3'
a. Write the protein sequence that is translated from this mRNA on the line below, and label the
amino (N) and carboxyl (C) termini of the protein.
(6 pts)
Version A: N-Met-Leu-Gly-Met-Ser-C
Version B: N-Met-Pro-Glu-Met-Val-C
-2 pts incorrect or missing N/C labels, -2 if started wrong AUG, -4 if translated entire mRNA, -1 for
writing "stop" in the amino acid sequence, -1 for each missing or incorrectly translated aa.
b. (1pt) How many tRNAs in total will
bind the ribosome during the
complete translation of this protein? 5
c. (5 pts) Put the following items in order (1-4) of when
they bind to the mRNA during translation. One item
does not directly bind mRNA, for that item write an
"X" in its blank.
+1 each correct ordered item, -2 if "X" incorrect
__3__ the large ribosomal subunit
__4__ release factor
__2__ a tRNA carrying f-Met
__X__ an amino-acyl tRNA synthetase
__1__ small ribosomal subunit
Codon Table
3
Biol 200, Autumn 2014
Exam 1, Key
N
6. (14 pts) The diagram to the right shows two
prokaryotic genes that are next to each other
on the bacterial chromosome. "Gene A"
5'
codes for an mRNA that is translated
into the protein "RNA polymerase".
3'
"Gene B" codes for a tRNA that carries
the amino acid valine (Val). "P" stands
for the promoter sequence and "T"
stands for the terminator sequence.
Gene A
P
Gene B
T
T
+1
+1
a. (2 pts) The two grey boxes in the promoter of gene B represent
the -35 and -10 regions. Which is more likely the -10 region? (Circle ONE)
C
C
D
b. (2 pts) Can these two genes be transcribed at the same time? Yes
Answer questions c-f with "gene A", "gene B", "both" or "neither":
c. (2 pts) Which gene uses the top strand as a template for transcription? Gene B
d. (3 pts) Which gene's promoter will bind sigma? both
e. (3 pts) Which gene has a sequence of T's and C's in the template strand close to +1? Gene A
f. (2 pts) For which gene will RNA polymerase end transcription at a stop codon? neither
7. (4 pts) The DNA below is a portion of a bacterial gene. One of the two ends of the DNA shown
represents the +1 base pair. RNA polymerase will be moving from right to left, as shown.
RNA polymerase
moving
What will the first 6 nucleotides of the RNA
transcribed be? (Circle the ONE best answer)
... 5' TAGGTAGCATAGAT 3' ...
... 3' ATCCATCGTATCTA 5' ...
a. 5' AGGUAG 3'
d. 5' AUCUAU 3'
b. 5' UCCAUC 3'
e. 5' UAGAUA 3'
c. 5' AUGGAU 3'
f. There is not enough information to answer this question
4
3'
5'
P
D
Biol 200, Autumn 2014
Exam 1, Key
N
8. (8 pts) Consider a molecule of glucose (C6H12O6)
and a molecule of the fatty acid shown to the right (C6H12O2).
For this question, one molecule of each type is completely
oxidized using cellular respiration. Note: fatty acids are
modified and enter the Krebs Cycle.
(2 pts for each blank)
a. Which has more potential energy stored in its bonds? the fatty acid
b. How many electron carriers will be reduced for glucose? 12 the fatty acid? 16
c. Which molecule will result in more CO2 as a product? (Circle ONE)
- glucose
- the fatty acid
- they produce the same amount
9. (20 pts) The reaction to the right occurs during the Krebs cycle.
Not all of the reactants or products are shown.
a. For each statement below, write an "X" in the T or F column.
(1 pt each)
T
F
T
F
_X__ ____
A carbon is oxidized.
____
__X_ In cells, this is an endergonic reaction.
__X_ ATP drives this reaction forward.
____
__X_ CO2 is a product.
____
____
__X_ Water is a product.
__X_ ____
An electron carrier is reduced.
b. (3 pts) Enzyme "X" catalyzes the reaction shown above. Can enzyme X catalyze different steps of
the Krebs cycle? Why or why not?
No. Each step of the Krebs cycle requires its own enzyme because enzymes are specific for
their substrates. (explanation must be reasonable for full credit)
c. (3 pts) Enzyme X is shown to the right. It consists of two identical
polypeptides. The pH of the matrix is 7.8. Which of the following levels of
structure will change if I place enzyme X in a solution at pH 13? (Choose ALL
correct answers)
- 1°
- 2°
- 3°
- 4°
d. (3 pts) Which of the following types of bonds will change if I place enzyme
X in a solution at pH 13? (Choose ALL correct answers)
- hydrogen bonds
- disulfide bonds
- ionic bonds
e. (2 pts) How many genes encode this enzyme? one
f. (3 pts) In eukaryotes, this Krebs cycle enzyme is encoded by DNA in the nucleus and the mRNA is
translated in the cytoplasm. What should be present in the sequence of the eukaryotic protein that
the prokaryotic version will not have?
A mitochondrial localization sequence
5