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USABO Open Exam 2014.
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USABO Open Exam 2014Why 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. - correct
answer-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. - correct answer-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 - correct answer-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 - correct answer-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.
- correct answer-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 - correct answer-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.
E. None of the above. - correct answer-B. The polymerase would not be able to conduct
proofreading during the replication process.
Some Archaea have structures called cannulae, which are hollow tubules made of
glycoprotein that connect cells. It is thought that the cannulae allow for the exchange of
nutrients and communication factors between archaeal cells. If this is so, which is the closest
analogue to cannulae from the list below?
A. Bacterial microtubules.
B. Archaeal hami.
C. Tight junctions in animal cells.
D. Plasmodesmata in plant cells.
E. Animal microtubules. - correct answer-D. Plasmodesmata in plant cells.
Which of the following is not a way for the cell to avoid accumulation of damaged and/or
malformed proteins?
A. Chaperonins.
B. Ubiquitination.
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