Garrod hypothesized that ʺinborn errors of metabolismʺ such as alkaptonuria occur because
genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes.
A mutation results in a defective enzyme A. Which of the following would be a consequence of that mutation?
an accumulation of A and no production of B and C
If A, B, and C are all required for growth, a strain that is mutant for the gene encoding enzyme A would be able to grow on which of the following media?
minimal medium supplemented with nutrient ʺBʺ only
The nitrogenous base adenine is found in all members of which group?
ATP, RNA, and DNA
Using RNA as a template for protein synthesis instead of translating proteins directly from the DNA is advantageous for the cell because
RNA acts as an expendable copy of the genetic material
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 nucleotides?
The enzyme polynucleotide phosphorylase randomly assembles nucleotides into a polynucleotide polymer. You add polynucleotide phosphorylase to a solution of adenosine triphosphate and guanosine triphosphate. How many artificial mRNA 3 nucleotide codons would be possible?
A particular triplet of bases in the template strand of DNA is 5ʹ AGT 3ʹ. The corresponding codon for the mRNA transcribed is
3ʹ UCA 5ʹ.
What amino acid sequence will be generated, based on the following mRNA codon sequence?
A peptide has the sequence NH2-phe-pro-lys-gly-phe-pro-COOH. Which of the following sequences in the coding strand of the DNA could code for this peptide?
What is the sequence of a peptide based on the following mRNA sequence? 5ʹ . . . UUUUCUUAUUGUCUU 3ʹ
The genetic code is essentially the same for all organisms. From this, one can logically assume all of the following except
DNA was the first genetic material.
The ʺuniversalʺ genetic code is now known to have exceptions. Evidence for this could be found if which of the following is true?
If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only).
Which of the following nucleotide triplets best represents a codon?
a triplet in the same reading frame as an upstream AUG
Which of the following is true for both prokaryotic and eukaryotic gene expression?
RNA polymerase binds to the promoter region to begin transcription.
In which of the following actions does RNA polymerase differ from DNA polymerase?
RNA polymerase can initiate RNA synthesis, but DNA polymerase requires a primer to initiate DNA synthesis.
Which of the following statements best describes the termination of transcription in prokaryotes?
RNA polymerase transcribes through the terminator sequence, causing the polymerase to fall off the DNA and release the transcript.
RNA polymerase moves in which direction along the DNA?
3ʹ → 5ʹ along the template strand
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?
It might allow the polymerase to recognize different promoters under certain environmental conditions.
Which of these is the function of a poly (A) signal sequence?
It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~10 —35 nucleotides away.
In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?
RNA polymerase II
Transcription in eukaryotes requires which of the following in addition to RNA polymerase?
several transcription factors (TFs)
A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which might this illustrate?
Any mutation in the sequence is selected against.
The TATA sequence is found only several nucleotides away from the start site of transcription. This most probably relates to which of the following?
the number of hydrogen bonds between A and T in DNA
Which of the following help(s) to stabilize mRNA by inhibiting its degradation?
5ʹ cap and poly (A) tail
What is a ribozyme?
an RNA with enzymatic activity
What are the coding segments of a stretch of eukaryotic DNA called?
A transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that
many noncoding stretches of nucleotides are present in mRNA.
Once transcribed, eukaryotic mRNA typically undergoes substantial alteration that includes
excision of introns.
Introns are significant to biological evolution because
their presence allows exons to be shuffled.
A mutation in which of the following parts of a gene is likely to be most damaging to a cell
Which of the following is (are) true of snRNPs?
They join together to form a large structure called the spliceosome.
During splicing, which molecular component of the spliceosome catalyzes the excision reaction?
Alternative RNA splicing
can allow the production of proteins of different sizes from a single mRNA.
In the structural organization of many eukaryotic genes, individual exons may be related to which of the following?
the various domains of the polypeptide product
Each eukaryotic mRNA, even after post-transcriptional modification, includes 5ʹ and 3ʹ UTRs. Which are these?
the untranslated regions at either end of the coding sequence
In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5ʹ cap and poly(A) tail. Which of the following would you expect him to find?
The molecule is digested by exonucleases since it is no longer protected at the 5ʹ end
A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is
Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the
bonding of the anticodon to the codon. attachment of amino acids to tRNAs.
A part of an mRNA molecule with the following sequence is being read by a ribosome: 5ʹ CCG-ACG 3ʹ (mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 3ʹ to 5ʹ direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form.
What type of bonding is responsible for maintaining the shape of the tRNA molecule?
hydrogen bonding between base pairs
The tRNA shown in Figure 17.4 has its 3ʹ end projecting beyond its 5ʹ end. What will occur at this 3ʹ end?
The amino acid binds covalently.
A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of a phenylalanine. The consequence of this for the cell will be that
proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.
There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that
the rules for base pairing between the third base of a codon and tRNA are flexible.
What is the most abundant type of RNA?
From the following list, which is the first event in translation in eukaryotes?
the small subunit of the ribosome recognizes and attaches to the 5ʹ cap of mRNA
Choose the answer that has these events of protein synthesis in the proper sequence 1. An aminoacyl-tRNA binds to the A site. 2. A peptide bond forms between the new amino acid and a polypeptide chain. 3. tRNA leaves the P site, and the P site remains vacant. 4. A small ribosomal subunit binds with mRNA. 5. tRNA translocates to the P site
4, 1, 2, 5, 3
As a ribosome translocates along an mRNA molecule by one codon, which of the following occurs?
The tRNA that was in the A site moves into the P site.
What are polyribosomes?
groups of ribosomes reading a single mRNA simultaneously
Which of the following is a function of a signal peptide?
to translocate polypeptides across the ER membrane
When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by
a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.
When does translation begin in prokaryotic cells?
as soon as transcription has begun
When a tRNA molecule is shown twisted into an L shape, the form represented is
its 3-dimensional shape.
An experimenter has altered the 3ʹ end of the tRNA corresponding to the amino acid methionine in such a way as to remove the 3ʹ AC. Which of the following hypotheses describes the most likely result?
The amino acid methionine will not bind.
A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already. Which enzyme causes a covalent bond to attach lysine to the polypeptide?
Where does tRNA #2 move to after this bonding of lysine to the polypeptide?
Which component of the complex described enters the exit tunnel through the large subunit of the ribosome?
newly formed polypeptide
The process of translation, whether in prokaryotes or eukaryotes, requires tRNAs, amino acids, ribosomal subunits, and which of the following?
polypeptide factors plus GTP
When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate?
an assembled ribosome with a polypeptide attached to the tRNA in the P site
Why might a point mutation in DNA make a difference in the level of proteinʹs activity?
It might substitute an amino acid in the active site.
In the 1920s Muller discovered that X-rays caused mutation in Drosophila. In a related series of experiments, in the 1940s, Charlotte Auerbach discovered that chemicalsshe used nitrogen mustardshave a similar effect. A new chemical food additive is developed by a cereal manufacturer. Why do we test for its ability to induce mutation?
We want to prevent any increase in mutation frequency
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?
a deletion of 2 nucleotide
What is the effect of a nonsense mutation in a gene?
It introduces a premature stop codon into the mRNA.
Each of the following options is a modification of the sentence THECATATETHERAT. Which of the following is analogous to a frameshift mutation?
Each of the following options is a modification of the sentence THECATATETHERAT. Which of the following is analogous to a single substitution mutation?
Sickle-cell disease is probably the result of which kind of mutation?
A frameshift mutation could result from
either an insertion or a deletion of a base.
Which of the following DNA mutations is the most likely to be damaging to the protein it specifies?
a base-pair deletion
Which point mutation would be most likely to have a catastrophic effect on the functioning of a protein?
a base deletion near the start of a gene
Which of the following statements are true about protein synthesis in prokaryotes?
Translation can begin while transcription is still in progress.
Gene expression in Archaea differs from that in other prokaryotes. It shares features with which of the following?
bacteria and eukaryotes
Of the following, which is the most current description of a gene?
a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
In eukaryotic cells, transcription cannot begin until
several transcription factors have bound to the promoter.
Which of the following is not true of a codon?
It extends from one end of a tRNA molecule.
The anticodon of a particular tRNA molecule is
complementary to the corresponding mRNA codon.
Which of the following is not true of RNA processing?
Exons are cut out before mRNA leaves the nucleus.
Which of the following mutations would be most likely to have a harmful effect on an organism?
a single nucleotide insertion downstream of, and close to, the start of the coding sequence
Which component is not directly involved in translation?