USABO Open Exam Questions and

USABO Open Exam  Questions and Verified Answers, 100% Score Guarantee Pass (Latest 2025) Which statement is true about enzymes? Enzymes

• Are made up of a base containing nitrogen, phosphate, and

ribose.

• Have activity that is independent of temperature and pH.
• Lose some or all of their normal activity when their 3-D

structure is disrupted.

• Provide the activation energy needed to activate a

reaction.

• Work once only and then are destroyed. - Correct

Answers ✅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?

• The cells contain plasmids.
• The cells have multiple forms of DNA polymerase.
• The cells have the majority of their genome stored in

circular DNA. 1 / 3

USABO Open Exam  Questions and Verified Answers, 100% Score Guarantee Pass (Latest 2025)

• The cells contain active telomerase.
• The cells contain active fissonase. - Correct Answers

✅D. The cells contain active telomerase.Which of the following correctly describes how the lifespan of a protein is regulated?

• The part of the sequence coded for by the UTR tags it for

destruction.

• Giant protein complexes called ubiquitins destroy proteins

after they have remained in the cell for a certain time.

• Proteins are methylated over time; heavily methylated

proteins are destroyed by proteasomes.

• Proteins are tagged with ubiquitins, which are recognized

by proteasomes; the proteasomes destroy the proteins.

• Proteins tagged with methyl groups are destroyed by

ubiquitins. - Correct Answers ✅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?

• Histidine 2 / 3

USABO Open Exam  Questions and Verified Answers, 100% Score Guarantee Pass (Latest 2025)

• Glutamate
• Cysteine
• Glycine
• Serine - Correct Answers ✅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?

• Chemical mutagens
• Beta emissions from radioactive decay
• Gamma rays
• X-rays
• UV rays - Correct Answers ✅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'

• 5'-CGCGCGCG-3'
• / 3