Mastering Genetics Ch. 12 – Flashcards
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Which of the following is a characteristic of RNA splicing in Eukaryotes?
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Exon/intron boundaries are typically characterized by a 5' GU splice junction and a 3' AG splice junction.
These splice junctions are recognized by the spliceosome so that accurate removal of introns is possible.
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A snRNP is best described as _______.
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Small RNAs associated with protein complexes in the nucleus.
snRNPs recognize the 5' and 3' splice junctions and the branch point sequence, excise the intron, and splice together the exons.
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Which of the following is most likely attributable to a base substitution at a 5' splice junction?
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A longer than usual final transcript.
Such a mutation could block intron removal, resulting in a longer than usual transcript.
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Start code.
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AUG
Methionine
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Stop codes.
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UAG
UGA
UAA
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Which of the following single base changes would result in alanine being substituted for threonine?
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A changed to G in the first position of the codon.
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Which of the following single base changes would result in serine being substituted for glycine?
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G changed to A in the first position of the codon.
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Which of the following single base changes would result in valine being substituted for isoleucine?
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A changed to G in the first position of the codon.
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Both the codons UUU and UUC specify the amino acid phenylalanine. What is the term for this phenomenon?
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Degenerate.
Degeneracy of the code means that a given amino acid can be specified by more than one triplet codon.
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How many different codons code for amino acids?
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61.
There are 61 codons that code for amino acids and three stop codons that do not code for an amino acid.
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RNA synthesis from a DNA template is called __________.
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Transcription.
Transcription is initiated when the cell signals for the expression of a particular gene and involves the synthesis of RNA from a DNA template.
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Which subunit of RNA polymerase establishes template binding to a promoter in prokaryotes?
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σ
The σ subunit recognizes the promoter sequence. Different sigma subunits can be employed to regulate the expression of genes at the transcriptional level.
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What are two main types of posttranscriptional modifications that take place in the mRNA of eukaryotes?
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The addition of a 7-mG cap at the 5' end of the transcript and the addition of a poly-A sequence at the 3' end of the message.
These are the two steps in the processing of eukaryotic mRNA.
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Assuming the code is a triplet, what effect would the addition or loss of six nucleotides have on the reading frame?
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Reestablishing of the subsequent reading frame
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If the code were a sextuplet (consisting of six nucleotides), would the reading frame be restored by the addition or loss of three nucleotides?
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No
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Six nucleotides?
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Yes
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Nine nucleotides?
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No
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The genetic code is degenerate, meaning that a codon can specify more than one amino acid.
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False.
The degeneracy of the genetic code means that an amino acid may be coded for by more than one codon. However, a single codon can only ever specify one amino acid.
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A DNA sequence produces a mutant protein in which several amino acids in the middle of the protein differ from the normal protein. What kind of mutation could have occurred?
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An addition and a deletion mutation.
A single addition or deletion would change the reading frame of the protein, but if another mutation occurred to cancel the effects of the first mutation, only those amino acids between the mutations would change.
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Which of the following statements about eukaryotic transcription is false?
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A polycistronic mRNA may be transcribed if the gene products are used in the same pathway or needed at the same time.
This statement is false. Polycistronic mRNAs are produced only in prokaryotes. In eukaryotes, a single gene is transcribed at a time.
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The genetic code is said to be triplet, meaning that there ________.
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are three bases in mRNA that code for an amino acid.
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A base at the first position of an anticodon on the tRNA would pair with a base at the ________ position of the mRNA.
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Third
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The triplet AUG is commonly used as a start codon during translation.
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True
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Of the following three types of nucleic acids—DNA, mRNA, tRNA—which is most likely to contain modified bases?
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tRNA
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Introns are known to contain termination codons (UAA, UGA, or UAG), yet these codons do not interrupt the coding of a particular protein. Why?
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Introns are removed from mRNA before translation.
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The relationship between a gene and a messenger RNA is that ________.
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mRNAs are made from genes
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Messenger RNA is usually polycistronic in eukaryotes.
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False
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When considering the initiation of transcription, one often finds consensus sequences located in the region of the DNA where RNA polymerase(s) binds. Which of the following is a common consensus sequence?
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TATA
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A 3' poly-A tail and a 5'-cap are common components of prokaryotic RNAs.
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False
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RNA processing occurs when amino acids are removed from nascent proteins.
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False
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Heterogeneous nuclear RNA is a primary transcript in eukaryotes that is processed prior to involvement in translation.
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True
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It has been recently determined that the gene for Duchenne muscular dystrophy (DMD) is more than 2000 kb (kilobases) in length; however, the mRNA produced by this gene is only about 14 kb long. What is a likely cause of this discrepancy?
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The introns have been spliced out during mRNA processing.
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In which cellular organelle do the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes occur?
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Nucleus
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An intron is a section of ________.
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RNA that is removed during RNA processing
