Chap 17 Flashcards
Which of the following variations on translation would be most disadvantageous for a cell?
translating polypeptides directly from DNA
“inborn errors of metabolism” such as alkaptonuria occur because…
metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies.
How might PKU affect the presence or absence of alkaptonuria?
It would have no effect, because Tyrosine is also available in the diet.
The nitrogenous base adenine is found in all members of which group?
ATP, RNA, and DNA
Triplet bases in the template strand of DNA is 5’AGT 3’. The corresponding codon for the mRNA transcribed is…
3’ UCA 5’
The genetic code is essentially the same for all organisms. What can be assumed?
A gene from an organism can theoretically be expressed by any other organism.
The universal genetic code can have exceptions. Evidence for this can be what?
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 is the same reading frame as as an upstream AUG
Which of the following provides some evidence that RNA probably evolved before DNA?
DNA polymerase uses primer, usually made of RNA
Which of the following 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
Which of the following 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
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
What is a 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. What 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. What will illustrate it?
any mutation in the sequence is selected against.
The TATA sequence is found only several nucleotides away from the site of transcription. This is most probably die to what?
The number of hydrogen bonds between A and T in DNA
What is a ribozyme?
An RNA with enzymatic activity
A transcription unit is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approx. 400 amino acids. This is best explained by the fact that…
many noncoding stretches of nucleotides are presentin mRNA
During the splicing, which molecular component of the spliceosome catalyzes the excision of the reaction?
RNA
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 what?
the various domains of polypeptide product
researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5’cap and poly- tail. What would happen?
The molecule digested by exonucleases since it is no longer protected at the 5’ end
5’ UTR E1 I1 E2 I2 E3 I3 E4 UTR 3’ What would be found in the mRNA cytosol?
5’ UTR E1 E2 E3 E4 UTR 3’
When the splicosome binds to elements of this structure, where can it attach?
to the end of the intron
Which of the following is a useful feature of introns for this model?
Introns allow exon shuffling
Exposure to a chemical mutagen results in a change in the sequence that alters the 5’ end of the intron 1 (I1). What might occur?
Inclusion of I1 in the mRNA
Suppose that an induced mutagen removes most of the 5’ end of the 5’ UTR. What might result?
Removal of the 5’ UTR also removes the 5’ cap and the mRNA will quickly degrade
A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds to the mRNA codon is…
UUU
Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on the specificity in the…
bonding of the anticodon to the codon and the attachment of amin acids to the tRNAs
What is the function of GTP in translation?
GTP energizes the formation of the initiation complex, using initiation factors
A mutant bacterial cell has a defective aminoacyl synthase that attaches lysine to tRNAs with the anticodon AAA instead of the normal phenylalnine. 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 of 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 the mRNA
What is the function of a single peptide?
translocate polypeptides across the ER membrane
When translating secretory or membrane proteins, ribosome are directed to the ER membrane by..
a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane
experimenter altered 3’ end of the tRNA corresponding to the amino acid methionine in such a way to remove the 3’ AC. What hypothesis describes result?
the amino acid methionine will not bind
The process of translation, whether in prokaryotes or eukaryotes, requires tRNAs, amino acids, ribosomal subunits and..
Polypeptide factors plus GTP
When the ribosome reaches the a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to experimentally be stopped at this point, what could you isolate?
An assembled ribosome with a polypeptide attached to the tRNA in the P site
What is the function of the release factor?
It binds to the stop codon in the A site in the place of a tRNA
When the function of the newly made polypeptide is to be secreted fromt the cell where it has been made, what might occur?
Its signal sequence must target it to the ER, from which it goes to the golgi
Suppose a mutation alters the formation fo the 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 for Leu)
One mutated tRNA - leu will not be relatively inconsequential because it will compete with many normal ones
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
Muller discovered x ray caused mutations in DRospholia. Nitrogen mustards have a similar effect. 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 error in the mRNA just after the AUG start of translation is likely to have the most serious effect on polypeptide product?
a deletion of 2 nucleotides
What is the effect of nonsense mutation in a gene?
It introduces a premature stop codon into the mRNA
A frameshift mutation can result from
either an insertion or a deletion of base
What DNA mutation is most likely to be damaging to the protein it specifies?
a base-pair deletion
Which small scale mutation would most likely to have catastrophic effect on the functioning of a protein?
a base deletion near the start of a gene
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
What mutation is most likely to cause a phenotypic change?
a single nucleotide deletion in an exon coding for an active site
If a protein is coded for a single gene and this protein has six clearly defined domains, which number of exons isthe gene likely to have?
8
What is true about protein synthesis in prokaryotes?
Translation can begin while transcription is still in progress
What is the most current definition of a gene?
DNA sequence that is expressed to form a functional product: either RNA or polypeptide
Gene expression in the domain Archaea in part resembles that of bacteria and in part that of domain Eukarya. I which way is it most like domai Eukarya?
Domain Archae have numerous transcription factors
What is true about domain archae?
roughly simultaneous with translation
Comparing DNA replication with RNA transcription in the same cell. What is only true of replication?
entire template molecule is represented in the product
In order for a eukaryotic gene to be engineered to go into a bacterial colony, what must be included along with the exons?
a bacterial promoter sequence
genome of a particular species is said to include 20,000 protein codin=g regions what does this mean?
al so genes for RNAs other than just mRNA
