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Location: USABO Open Exam 2012 2012 USABO Open Exam Page 1 1. Rank the following biological molecules in order of how readily they diffuse across the plasma membrane from the most diffusible to the least diffusible. I. CO2 II. ClIII. Sucrose IV. Glycerol A. I, III,

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USABO Open Exam
February 5 to 15, 2013
1. Which statement is true about enzymes? Enzymes
A. Are made up of a base containing nitrogen, phosphate, and ribose.
B. Have activity that is independent of temperature and pH.
C. Lose some or all of their normal activity when their 3-D structure is disrupted.
D. Provide the activation energy needed to activate a reaction.
E. Work once only and then are destroyed.
2. You have a multicellular organism that reproduces asexually by fission. When you excise
a ~10,000 cell portion of its body, both the original organism and the excised portion
grow into fully formed, healthy organisms. You take one of the offspring and repeat the
procedure for one hundred and twenty-three generations. Each time, the resulting
organisms are healthy. What must be true of the nuclei of this species?
A. The cells contain plasmids.
B. The cells have multiple forms of DNA polymerase.
C. The cells have the majority of their genome stored in circular DNA.
D. The cells contain active telomerase.
E. The cells contain active fissonase.
3. Which of the following correctly describes how the lifespan of a protein is regulated?
A. The part of the sequence coded for by the UTR tags it for destruction.
B. Giant protein complexes called ubiquitins destroy proteins after they have remained in the
cell for a certain time.
C. Proteins are methylated over time; heavily methylated proteins are destroyed by
proteasomes.
D. Proteins are tagged with ubiquitins, which are recognized by proteasomes; the proteasomes
destroy the proteins.
E. Proteins tagged with methyl groups are destroyed by ubiquitins.2013 USABO Open Exam Page 2
4. Of the following amino acids, which is least likely to form strong interactions with other
amino acids that contribute to the tertiary structure of a given protein?
A. Histidine
B. Glutamate
C. Cysteine
D. Glycine
E. Serine
5. Thymine dimers arise when two adjacent thymine bases become covalently linked. This
interferes with normal DNA geometry and will cause replication errors. Which of the
following agents is the primary cause of the thymine dimers?
A. Chemical mutagens
B. Beta emissions from radioactive decay
C. Gamma rays
D. X-rays
E. UV rays
6. Which of the following oligonucleotides would have the highest melting point when
paired with the proper complementary strand?
A. 5’-AAAAAAAA-3’
B. 5’-ATGCATGC-3’
C. 5’-CGCGCGCG-3’
D. 5’-TTTTGGGG-3’
E. 5’-TATATATA-3’
7. Which of the following is a way in which the cell increases gene expression in the
nucleus?
A. Acetylation of histone tails
B. DNA methylation
C. Locating a gene within heterochromatin
D. Dephosphorylating DNA
E. Alternative splicing
8. Below are the structures of five amino acids. Select the amino acid that would contribute
most significantly to stability of the tertiary structure of a protein.
\A. B. C. D. E.2013 USABO Open Exam Page 3
9. Which of the following statements about cellular ultrastructure is FALSE?
A. Nonmotile eukaryotic cilia are composed of 9 doublets of microtubules in a ring, with no
microtubules in the center (‘9+0’).
B. Bacterial flagella are composed of 9 doublets of microtubules in a ring, with two
microtubules in the center (‘9+2’).
C. Motile eukaryotic cilia are composed of 9 doublets of microtubules in a ring, with two
microtubules in the center (‘9+2’).
D. Centrioles are composed of nine triplets of microtubules arranged in a ring.
E. The basal bodies of eukaryotic flagella are composed of nine triplets of microtubules
arranged in a ring.
10. In a secret cabinet of a lab, you find two Petri dishes in storage and a mysterious lab
notebook. In an effort to identify the bacteria, you run some tests (taking all necessary
safety precautions) and look through the lab notebook. You find that the two Petri
dishes contain the same type of nutrient medium and both bacteria seem to be
Escherichia sp., but that the bacteria in plate 1 are producing large amounts of a variety
of neurotoxins. The bacteria in plate 2 are not producing any major exported product.
You also find this chart in the lab notebook:
Given that Strain 2 is normal E.coli (the control) and Strain 1 is a genetically engineered
strain of E.coli, which line is most likely to represent strain 1, and why?
A. Line B, since strain 1 should exhibit lower than normal growth efficiency.
B. Line B, since strain 1 should exhibit higher than normal growth efficiency.
C. Line A, since strain 1 should exhibit lower than normal growth efficiency.
D. Line A, since strain 1 should exhibit higher than normal growth efficiency.
E. The E. coli line should represent both, since Strain 1 should have the same growth efficiency
as a normal E. coli strain.2013 USABO Open Exam Page 4
11. Which of the following chemicals or groups of chemicals is not a major determinant of
flower color?
A. Flavonols
B. Carotenoids
C. Cyanidin
D. Phytoalexins
E. Betacyanins
12. Which of the following is not a characteristic of cycads?
A. Secondary growth from a vascular cambium
B. Fruit
C. True leaves
D. Insect pollination
E. Presence of neurotoxins and carcinogens in plant tissues
13. Which of the following does not take part in the light reactions of photosynthesis?
A. Photosystem I
B. Photosystem II
C. Rubisco
D. ATP synthase
E. Cytochrome complex
14. Lettuce seeds receive flashes of far red and red light in this order: far red, red, far red,
red, red, red, red, far red. The seeds will
A. Germinate since far red light induces germination.
B. Germinate since the first flash of light determines germination.
C. Germinate since there are more flashes of red light.
D. Not germinate since the flashes of light have destroyed the seeds.
E. Not germinate since only the last flash of light determines germination.
15. Which of the following statements about alternation of generations in land plants is
TRUE?
A. The gametophyte produces haploid cells by meiosis.
B. In nonvascular plants (Bryophyta), the gametophyte stage is dominant.
C. The sporophyte produces diploid spores that later undergo meiosis.
D. The gametophyte stage is diploid.
E. (A) and (D) are BOTH true. 2013 USABO Open Exam Page 5








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