Campbell Biology: Chap 17
A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is
3' UCA 5'.
If a protein is coded for by a single gene and this protein has six clearly defined domains, what number of exons is the gene likely to have?
8
The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?
A gene from an organism can theoretically be expressed by any other organism.
What does not occur in prokaryotic eukaryotic gene expression, but does in eukaryotic gene expression?
A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end.
The nitrogenous base adenine is found in all members of which group?
ATP, RNA, and DNA
A part of the promoter, called the TATA box, is said to be highly conserved in evolution. What might this illustrate?
Any mutation in the sequence is selected against.
What component is not directly involved in translation?
DNA
What best provides some evidence that RNA probably evolved before DNA?
DNA polymerase uses primer, usually made of RNA.
Gene expression in the domain Archaea in part resembles that of bacteria and in part that of the domain Eukarya. In what way is it most like the domain Eukarya?
Domain Archaea have numerous transcription factors.
What is not true of RNA processing?
Exons are cut out before mRNA leaves the nucleus.
What is the function of GTP in translation?
GTP energizes the formation of the initiation complex, using initiation factors.
The "universal" genetic code is now known to have exceptions. Evidence for this can be found if what 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).
What is the function of the release factor (RF)?
It binds to the stop codon in the A site in place of a tRNA.
What is a function of a poly-A signal sequence?
It codes for a sequence in eukaryotic transcripts that signals enzymatic cleavage ~1035 nucleotides away.
What is the effect of a nonsense mutation in a gene?
It introduces a premature stop codon into the mRNA.
What is true of transcription in domain Archaea?
It is roughly simultaneous with translation.
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. What 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.
Why might a point mutation in DNA make a difference in the level of protein's activity?
It might substitute an amino acid in the active site.
Garrod's information about the enzyme alteration resulting in alkaptonuria led to further elucidation of the same pathway in humans. Phenylketonuria (PKU) occurs when another enzyme in the pathway is altered or missing, resulting in a failure of phenylalanine (phe) to be metabolized to another amino acid: tyrosine. Tyrosine is an earlier substrate in the pathway altered in alkaptonuria. How might PKU affect the presence or absence of alkaptonuria?
It would have no effect, because tyrosine is also available from the diet.
When the function of the newly made polypeptide is to be secreted from the cell where it has been made, what must occur?
Its signal sequence must target it to the ER, from which it goes to the Golgi.
It extends from one end of a tRNA molecule. Is this true of a codon?
No
Suppose that a mutation alters the formation of a tRNA such that it still attaches to the same amino acid (phe) but its anticodon loop has the sequence AAU that binds to the mRNA codon UUA (that usually specifies leucine leu).
One mutated tRNA molecule will be relatively inconsequential because it will compete with many "normal" ones.
ring splicing, which molecular component of the spliceosome catalyzes the excision reaction?
RNA
n eukaryotes there are several different types of RNA polymerase. What type is involved in transcription of mRNA for a globin protein?
RNA polymerase II
What best describes the termination of transcription in prokaryotes?
RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.
An experimenter has altered the 3' end of the tRNA corresponding to the amino acid methionine in such a way as to remove the 3' AC. What is the most likely result?
The amino acid methionine will not bind.
In comparing DNA replication with RNA transcription in the same cell, what is true only of replication?
The entire template molecule is represented in the product.
In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5' cap and poly-A tail. What would you expect him to find?
The molecule is digested by exonucleases since it is no longer protected at the 5' end.
When the genome of a particular species is said to include 20,000 protein-coding regions, what does this imply?
There are also genes for RNAs other than mRNA.
What is true about protein synthesis in prokaryotes?
Translation can begin while transcription is still in progress.
A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is
UUU.
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 chemicals-she used nitrogen mustards-have 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.
What is the most current description of a gene?
a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what must be included in addition to the coding exons of the gene?
a bacterial promoter sequence
What small-scale 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
What of the following DNA mutations is the most likely to be damaging to the protein it specifies?
a base-pair deletion
What 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 two nucleotides
The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in
a polypeptide missing an amino acid.
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.
What mutation is most likely to cause a phenotypic change?
a single nucleotide deletion in an exon coding for an active site
What 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
What nucleotide triplets best represents a codon?
a triplet in the same reading frame as an upstream AUG
What is a ribozyme?
an RNA with enzymatic activity
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, what would you be able to isolate?
an assembled ribosome with a polypeptide attached to the tRNA in the P site
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 and the attachment of amino acids to tRNAs.
Alternative RNA splicing
can allow the production of proteins of different sizes from a single mRNA.
The anticodon of a particular tRNA molecule is
complementary to the corresponding mRNA codon.
A frameshift mutation could result from
either an insertion or a deletion of a base.
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.
Garrod hypothesized that "inborn errors of metabolism" such as alkaptonuria occur because
metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies.
The process of translation, whether in prokaryotes or eukaryotes, requires tRNAs, amino acids, ribosomal subunits, and which of the following?
polypeptide factors plus GTP
A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal 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.
Transcription in eukaryotes requires what of the following in addition to RNA polymerase?
several transcription factors (TFs)
In eukaryotic cells, transcription cannot begin until
several transcription factors have bound to the promoter.
The TATA sequence is found only several nucleotides away from the start site of transcription. This most probably relates to what?
the number of hydrogen bonds between A and T in DNA
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 first event to take place in translation in eukaryotes?
the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA
In the structural organization of many eukaryotic genes, individual exons may be related to what?
the various domains of the polypeptide product
What is a function of a signal peptide?
to translocate polypeptides across the ER membrane
What variations on translation would be most disadvantageous for a cell?
translating polypeptides directly from DNA
