USABO Open Exam Questions and Answers
(2026) | Guaranteed Success | 100%
Correct
• 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. -✓✓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. -
✓✓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 -✓✓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 -✓✓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' -✓✓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
(2026) | Guaranteed Success | 100%
Correct
• 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. -✓✓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. -
✓✓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 -✓✓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 -✓✓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' -✓✓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
