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Bio blue thread _ exam 4 - (ch17)

Terms in this set (25)

Are the RNA and DNA strands parallel or antiparallel? In which direction is the DNA template "read"?
RNA and DNA strands are anti-parallel. The DNA template is read 3'->5' (while RNA is synthesized 5'->3')
Explain why bacterial terminator sequences are expected to vary more than bacterial promoter sequences.
Terminator sequences require formation of a hairpin loop in the RNA. Any DNA sequence that create 2. complementary sequences in RNA separated by a hairpin loop, + a huge number of DNA sequences will do this. Promoters must have a specific sequence that allows a sigma protein to bind, For this reason, promoters can have only a limited number of sequences.
Explain how the function of eukaryotic general transcription factors is more similar to the bacterial sigma protein than it is to the bacterial core RNA polymerase.
The general transcription factors recognize the promotor sequence but are not directly involved in the synthesis of RNA, which is the role of the bacterial core enzyme.
POS: if introns were not present, what would the micrograph in part (a) look like?
There would be no loops. This is because the molecules would match up exactly if the DNA lacked introns.
Give an example of an exon or part of an exon that does not code for amino acids.
The 5' and 3' UTRs, which do no code for amino acids, are either exon or parts of exon because they are present in the mRNA.
Explain how the RNA of spliceosomes is able to recognize which areas of a primary transcript to splice.
Base pairing between sequences in the primary transcripts and small nuclear RNAs of snRNPs that make up the spliceosome allows recognition of the regions to be spliced.
Predict the effect of removing the 5' cap from an mRNA.
The mRNA could not be used to start a new round of translation (because the ribosome couldn't begin translation without the cap) and the mRNA would be degraded from the 5' end (because the protective cap is no longer present).
Explain why the polyribosomes can be found in both bacteria and eukaryotes, but only bacteria can make use of linked transcription and translation.
Because polyribosomes occur when two or more ribosomes are simultaneously translating a single mRNA, this ca occur in both the cytoplasm of a eukaryotic cell or a bacterial cell. In contrast, linked transcription and translation requires both of these processes to occur in the same place and at the same, something that's impossible in a eukaryotic cell that transcribes and processes RNA in the nucleus, but translates RNA in the cytoplasm.
Explain why base pairing between an adapter molecule and codons in mRNA seemed a much more likely way to read the genetic code than matching amino acids directly to codons.
There is no clear way to match particular amino acids to particular codons, but there is an easy way to specifically read codons by having a base sequence in a hypothesized adapter molecule that is complementary to the codon being read.
POS: What would the graphed results look like if the null hypothesis were correct?
If the AA stayed attached to the tRNAs, the gray Lin would stay high and the green line low. If the AA were transferred to some other cell component, the gray line would decline but the green line would remain low.
(1) describe where the amino acid attaches and (2) explain the relationship between the anticodon of a tRNA and a codon in an mRNA.
(1) The amino acid attaches on the 3' end of the arm of the L-shaped structure that is farthest from the anticodon loop. (2) the anticodon is antiparallel in orientation the mRNA codon, and it contains the complementary bases.
Explain how tRNA fulfills the adapter role proposed by Crick.
Two parts of the tRNA let it act as an adapter: the anticodon can read codons, and the amino acid attachment site allows the TRNA to bring the amino acid that's specified by the codon to the ribosome. tRNA essentially acts as a bridge that links codons to amino acids.
Predict the average number of different tRNA molecules that can be recognized by a single type of aminoacyl tRNA synthetase.
Two. (because there are about 40 different types of tRNA and 20 different aminoacyl transferases)
Predict the number of different tRNAs that would be required if wobble pairing did not occur.
61. (wobble pairing allows one tRNA to read more than one codon. Without it, there would have to be one tRNA for each 61 amino-acid specifying codons.
Explain why it's important that the initiation tRNA be placed in the P site instead of the A site.
Having the initiator tRNA in the P site is important because if the polypeptide chain is to grow, the A site must be empty to allow the next amino-acyl tRNA to come into the ribosome.
Explain how a tRNA that was once in the A site comes to be in the P site during the elongation phase of translation.
After transfer of the polypeptide form the tRNA in the P site to the tRNA in the A site, the ribosome moves (translocates) one codon down the mRNA. The tRNAs remain bound to their codons as the ribosomes move. This event shifts the position of the tRNAs within the tRNA bending sites of the ribosome so that the tRNA that was in the A site is now in the P site.
Explain why it's logical that a release factor has the same structure as an aminoacyl tRNA.
Because the release factor binds to the same A site in the ribosome normally occupied by an aminoacyl tRNA, the shape of the releases factor and aminoacyl tRNA must be nearly identical to allow for a good fit.
What does a bacterial RNA polymerase produce when it transcribes a protein-coding gene?
C. mRNA
Where is the start codon located?
C. at the downstream end of the 5' untranslated region (UTR)
Splicing begins:
A. as transcription occurs
Compared with mRNAs that have a cap and tail, predict what will be observed if a eukaryotic mRNA lacked a cap and poly(A)tail.
B. Translation would occur inefficiently
RNases and proteases are enzymes that destroy RNAs and proteins, respectively. Which of the following enzymes, if added to a spliceosome, would be predicted to prevent recognition of pre-mRNA regions critical for splicing?
B. an RNase specific for snRNAs
True or False: genetic code
Wobble pairing accounts for the redundancy of the genetic code
There are 64 different tRNAs that read the 64 possible codons.
All possible codons are used, but not all codons specify an amino acid.
Some codons are recognized by proteins, not by tRNAs.
F
F
T
T
Imagine that when a bacterial cell carrying such a mutation is shifted form low to high growth temps, RNA polymerases in the process of elongation complete transcription normally, but no new transcripts can be started. The mutation in this strain most likely affects:
C. sigma
In what ways are a promoter and a start codon similar? In what ways are they different?
A promoter and a start codon are similar in that both are sequences of nucleic acids that are required to start important processes, and both determine the sites where the process will begin. The key differences are that the promoter is needed to start transcription and the start codon is needed to start translation. Also, the promoter is a DNA sequence only, and the start codon is a sequence found within an mRNA.
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