Chapter 13: The Genetic Code and Transcription Flashcards
True or False?
The genetic code is degenerate, meaning that a codon can specify more than one amino acid.
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.
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?
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.
True or False?
A polycistronic mRNA may be transcribed if the gene products are used in the same pathway or needed at the same time.
FALSE
Polycistronic mRNAs are produced only in prokaryotes. In eukaryotes, a single gene is transcribed at a time.
The following statements about eukaryotic transcription are true…
Transcription initiation occurs when RNA polymerase binds to a complex of transcription factors at the TATA box.
Eukaryotic promoter regions contain a TATA box and a CAAT box.
The transcripts produced contain both exons and introns.
Both the codons UUU and UUC specify the amino acid phenylalanine. What is the term for this phenomenon?
Degenerate
Degeneracy of the code means that a given amino acid can be specified by more than one triplet codon.
True or False?
The code is nonoverlapping, meaning that, assuming “standard translation,” a given base participates in the specification of one and only one amino acid.
True
The genetic code is said to be triplet, meaning that there ________.
are three bases in mRNA that code for an amino acid
Which type of mutation helped lead to the understanding that the genetic code is based on triplets?
Frameshift
Insertions or deletions of one or two nucleotides resulted in frameshift mutations. Insertion or deletion of three nucleotides resulted in insertion or deletion of a single amino acid and did not shift the reading frame.
A class of mutations that results in multiple contiguous (side-by-side) amino acid changes in proteins is probably caused by which of the following type of mutation?
frameshift
Significant in the deciphering of the genetic code was the discovery of the enzyme polynucleotide phosphorylase. What is this enzyme used for?
manufacture of synthetic RNA for cell-free systems
In 1964, Nirenberg and Leder used the triplet binding assay to determine specific codon assignments. A complex of which of the following components was trapped in the nitrocellulose filter?
charged tRNA, RNA triplet, and ribosome
All of the following experiments or discoveries helped to identify the “triplet nature” of the DNA code:
Anticodons
Repeating copolymers
Frameshift mutations
True or False?
The Universality of the genetic code discovery helped to identify the “triplet nature” of the DNA code.
FALSE
The universality of the code refers to the fact that, for the most part, all the DNA code of life’s genomes can be read in the same way. In other words, a codon that represents leucine in bacteria, will also represent leucine in humans.
Introns are known to contain termination codons (UAA, UGA, or UAG), yet these codons do not interrupt the coding of a particular protein. Why?
Introns are removed from mRNA before translation.
When examining the genetic code, it is apparent that ________.
there can be more than one codon for a particular amino acid
The genetic code is fairly consistent among all organisms. The term often used to describe such consistency in the code is ________.
universal
RNA synthesis from a DNA template is called _______.
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.
The relationship between a gene and a messenger RNA is that ________.
mRNAs are made from genes
Which subunit of RNA polymerase establishes template binding to a promoter in prokaryotes?
Sigma
The sigma subunit recognizes the promoter sequence. Different sigma subunits can be employed to regulate the expression of genes at the transcriptional level.
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?
TATA
True or False?
Messenger RNA is usually polycistronic in eukaryotes.
False
What are two main types of posttranscriptional modifications that take place in the mRNA of eukaryotes?
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.
True or False?
A 5’-cap describes the addition of a base, usually thymine, to the 5’ end of a completed peptide.
False
True or False?
A 3’ poly-A tail and a 5’-cap are common components of prokaryotic RNAs.
False