If proteins were composed of only 12
different kinds of amino acids, what would
be the smallest possible codon size in a
genetic system with four different
The genetic code is essentially the same for
all organisms. From this, one can logically
assume all of the following except
1. a gene from an organism could
theoretically be expressed by any other
2. all organisms have a common ancestor.
3. DNA was the first genetic material.
4. the same codons in different organisms
usually translate into the same amino acids.
In which of the following actions does RNA
polymerase differ from DNA polymerase?
1. RNA polymerase uses RNA as a template,
and DNA polymerase uses a DNA template.
2. RNA polymerase is much more accurate
than DNA polymerase.
3. RNA polymerase can initiate RNA
synthesis, but DNA polymerase requires a
primer to initiate DNA synthesis.
4. RNA polymerase does not need to
separate the two strands of DNA in order to
synthesize an RNA copy, whereas DNA
polymerase must unwind the double helix
before it can replicate the DNA.
RNA polymerase in a prokaryote is
composed of several subunits. Most of
these subunits are the same for the
transcription of any gene, but one, known
as sigma, varies considerably. Which of the
following is the most probable advantage
for the organism of such sigma switching?
1. It might allow the transcription process
to vary from one cell to another.
2. It might allow the polymerase to
recognize different promoters under certain
3. It could allow the polymerase to react
differently to each stop codon.
4. It could allow ribosomal subunits to
assemble at faster rates.
In eukaryotes there are several different
types of RNA polymerase. Which type is
involved in transcription of mRNA for a
2. RNA polymerase I
3. RNA polymerase II
4. RNA polymerase III
What is a ribozyme?
1. an enzyme that uses RNA as a substrate
2. an RNA with enzymatic activity
3. an enzyme that catalyzes the association
between the large and small ribosomal
4. an enzyme that synthesizes RNA as part
of the transcription process
Introns are significant to biological
1. their presence allows exons to be
2. they protect the mRNA from
3. they are translated into essential amino
4. they maintain the genetic code by
preventing incorrect DNA base pairings.
During splicing, which molecular
component of the spliceosome catalyzes
the excision reaction?
There are 61 mRNA codons that specify an
amino acid, but only 45 tRNAs. This is best
explained by the fact that
1. some tRNAs have anticodons that
recognize four or more different codons.
2. the rules for base pairing between the
third base of a codon and tRNA are flexible.
3. many codons are never used, so the
tRNAs that recognize them are dispensable.
4. the DNA codes for all 61 tRNAs but some
are then destroyed.
What is the most abundant type of RNA?
As a ribosome translocates along an mRNA
molecule by one codon, which of the
1. The tRNA that was in the A site moves
into the P site.
2. The tRNA that was in the P site moves
into the A site.
3. The tRNA that was in the A site moves to
the E site and is released.
4. The tRNA that was in the A site departs
from the ribosome via a tunnel.
What are polyribosomes?
1. groups of ribosomes reading a single
2. ribosomes containing more than two
3. multiple copies of ribosomes associated
with giant chromosomes
4. aggregations of vesicles containing
When does translation begin in prokaryotic cells?
1.after a transcription initiation complex has been formed
2.as soon as transcription has begun
3.after the 5 caps are converted to mRNA
4.once the pre-mRNA has been converted to mRNA
When a tRNA molecule is shown twisted into an L shape, the form represented is
1.its linear sequence.
2.its 2-dimensional shape.
3.its 3-dimensional shape.
4.its microscopic image.
Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product?
1.a deletion of a codon
2.a deletion of 2 nucleotides
3.a substitution of the third nucleotide in an ACC codon
4.a substitution of the first nucleotide of a GGG codon
Of the following, which is the most current description of a gene?
1.a unit of heredity that causes formation of a phenotypic characteristic
2.a DNA subunit that codes for a single complete protein
3.a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
4.a DNA—RNA sequence combination that results in an enzymatic product
The lactose operon is likely to be transcribed when
1.there is more glucose in the cell than lactose.
2.the cyclic AMP levels are low.
3.there is glucose but no lactose in the cell.
4.the cyclic AMP and lactose levels are both high within the cell.
Transcription of the structural genes in an inducible operon
1.occurs continuously in the cell.
2.starts when the pathway's substrate is present.
3.starts when the pathway's product is present.
4.stops when the pathway's product is present.
Muscle cells and nerve cells in one
species of animal owe their
differences in structure to
1. having different genes.
2. having different chromosomes.
3. using different genetic codes.
4. having different genes
In both eukaryotes and prokaryotes, gene expression is primarily regulated at the level of