USABO Open Exam
Why is myelin important in the nervous system?
A. It allows signals to travel faster along axons because depolarization occurs only at
myelinated locations.
B. It allows signals to travel faster along axons because depolarization occurs only at
nonmyelinated locations.
C. It bundles the dendrites of adjacent neurons together.
D. It increases capacitance across the cell membrane, which helps electrical signals to
leave the axons.
E. It traps neurotransmitters, increasing their concentrations in the synaptic cleft. -
ANS-B
Which type of cytoskeletal fiber is the primary building block of eukaryotic cilia and
flagella?
A. Actin microfilaments.
B. Intermediate filaments.
C. Keratin.
D. Microtubules.
E. RNA. - ANS-D. Microtubules.
Which of the following human cell types contains the LEAST amount of RNA involved in
splicing?
A. Lymphocytes
B. Lymphoblasts
C. Erythrocytes
D. Erythroblasts
E. Hepatocytes - ANS-C. Erythrocytes
Antimicrobial drugs, also known as antibiotics, inhibit the growth of bacteria by targeting
cellular components present in bacteria. Which of the following cellular components is
NOT a valid antimicrobial drug target?
A. Centrosome.
B. Ribosome.
C. Cell wall.
, D. RNA polymerase.
E. DNA polymerase - ANS-A. Centrosome.
Which of the following statements concerning the nature of post-transcriptional
processing of mRNA is INCORRECT?
A. The presence of introns is a derived trait of eukaryotes.
B. Mitochondrial mRNA lacks a 5′ cap because capping is a strictly intranuclear
process.
C. Recognition of splice sites by the spliceosome is based on the physical conformation
of the mRNA strand, not on any specific consensus sequence.
D. In some genes, poly-A tails can generate genetic diversity by being added at one of
multiple possible sites on the mRNA transcript.
E. Both 5′ caps and poly-A tails inhibit the degradation of the mRNA molecule in the
cytosol. - ANS-C. Recognition of splice sites by the spliceosome is based on the
physical conformation of the mRNA strand, not on any specific consensus sequence.
Cellular metabolism is bidirectional and complex. Indicate whether the following
statements concerning the metabolic capabilities of a nucleated human cell are True or
False.
A. Can convert sugars to fats
B. Can convert fats to sugars
C. Can convert sugars to amino acids
D. Can convert amino acids to sugars - ANS-A. True
B. False
C. True
D. True
Consider the 5' to 3' nature of polymerase and its secondary functions and the structure
of a nucleotide and its incorporation into a growing polynucleotide chain. Select the best
possible explanation below for why evolution has favored 5' to 3' polymerases, as
opposed to 3' to 5' ones.
A. Binding of a 3' to 5' polymerase to DNA would be impaired.
B. The polymerase would not be able to conduct proofreading during the replication
process.
C. The active site of such a polymerase would be unable to incorporate the nucleotide
substrate.
D. The polynucleotide chain elongation reaction can only occur in a 5' to 3' manner.
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