USABO Open Exam
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. - ANS-C. Lose some or all of their normal
activity when their 3-D structure is disrupted.
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. - ANS-D. The cells contain active telomerase.
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. - ANS-D. Proteins
are tagged with ubiquitins, which are recognized by proteasomes; the proteasomes
destroy the proteins.
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 - ANS-D. Glycine
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 - ANS-E. UV rays
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' - ANS-C. 5'-CGCGCGCG-3'
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 - ANS-A. Acetylation of histone tails
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').
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