Mastering Biology Chapter 17
What is a knock out mutation?
A knock-out mutation refers to the loss of a protein's function but not necessarily to its complete absence.
If a DNA sequence is altered from TAGCTGA to TAGTGA, what kind of mutation has occurred?
Deletion
What is meant by translocation?
The ribosome slides one codon down the mRNA.
The process of translation, or protein synthesis, is a crucial part of the maintenance of living organisms. Proteins are constantly in use and will break down eventually, so new ones must always be available. If protein synthesis breaks down or stops, then the organism dies.
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RNA polymerase moves in which direction along the DNA?
3' to 5' along the template strand
What is the process called that converts the genetic information stored in DNA to an RNA copy?
Transcription
RNA processing converts the RNA transcript into _____.
mRNA
A codon consists of _____ bases and specifies which _____ will be inserted into the polypeptide chain.
three ... amino acid
What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?
transcription
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'.
What determines which base is to be added to an RNA strand during transcription?
Base pairing between the DNA template strand and the RNA nucleotides
Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?
Complementary
Which one of the following is true of tRNAs?
Each tRNA binds a particular amino acid.
What is the effect of a nonsense mutation in a gene?
It introduces a premature stop codon into the mRNA.
Where does RNA polymerase begin transcribing a gene into mRNA?
It starts after a certain nucleotide sequence called a promoter.
Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)?
One addition and one deletion mutation.
DNA does not store the information to synthesize which of the following?
Organelles
Which of the following processes is an example of a post-translational modification?
Phosphorylation
What name is given to the process in which pre-mRNA is edited into mRNA?
RNA processing
Where does translation take place?
Ribosome
Which of the following steps occurs last in the initiation phase of translation?
The large ribosomal subunit joins the complex.
Which of the following statements best describes the promoter of a protein-coding gene?
The promoter is a nontranscribed region of a gene. The promoter is the regulatory region of a protein-coding gene at which RNA polymerase must bind to initiate transcription—it is not transcribed into the RNA.
If the sequence ATGCATGTCAATTGA were mutated such that a base were inserted after the first G and the third T were deleted, how many amino acids would be changed in the mutant protein?
Two.
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.
Of the following, which is the most current description of a gene?
a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
Which of the following DNA mutations is the most likely to be damaging to the protein it specifies?
a base-pair deletion
What is a ribozyme?
a biological catalyst made of RNA
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 and functions from a single mRNA.
Translation occurs in the _____.
cytoplasm
During RNA processing a(n) _____ is added to the 3' end of the RNA.
A poly-A tail is added to the 3' end of the RNA.
Transcription begins at a promoter. What is a promoter?
A site in DNA that recruits the RNA Polymerase This is the site where the RNA polymerase must bind to initiate transcription.
At which site do new aminoacyl tRNAs enter the ribosome during elongation?
A-site
If a mutated DNA sequence produces a protein that differs in one central amino acid from the normal protein, which of the following kinds of mutations could have occurred?
An addition mutation and a deletion mutation.
A part of the promoter, called the TATA box, is said to be highly conserved in evolution. Which of the following might this illustrate?
Any mutation in the sequence is selected against.
True or false? A codon is a group of three bases that can specify more than one amino acid.
False A codon is a group of three bases that can specify only one amino acid.
True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.
False There are no tRNAs complementary to the three stop codons; termination occurs when release factors recognize the stop codon in the A-site and catalyze the release of the polypeptide from the tRNA in the P-site.
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 happens to RNA polymerase II after it has completed transcription of a gene?
It is free to bind to another promoter and begin transcription.
What is the function of RNA polymerase?
It unwinds the double helix and adds nucleotides to a growing strand of RNA.
Which of the following statements 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.
How is translation initiated?
The small ribosomal subunit binds to the mRNA. The tRNA bearing methionine binds to the start codon. The large ribosomal subunit binds to the small one. The start codon signals the start of translation.
The figure represents tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid?
UUC
What does a mutagen cause?
a change in the sequence of DNA
Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene?
a frameshift deletion at the beginning of the gene
Polypeptides are assembled from _____.
amino acids
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, which of the following would you be able to isolate?
an assembled ribosome with a polypeptide attached to the tRNA in the P site
A frameshift mutation could result from
either an insertion or a deletion of a base.
The RNA segments joined to one another by spliceosomes are _____.
exons
What type of bonding is responsible for maintaining the shape of the tRNA molecule?
hydrogen bonding between base pairs
Which nucleic acid is translated to make a protein?
mRNA
What amino acid sequence will be generated, based on the following mRNA codon sequence? 5' AUG-UCU-UCG-UUA-UCC-UUG 3'
met-ser-ser-leu-ser-leu
During RNA processing a(n) _____ is added to the 5' end of the RNA.
modified guanine nucleotide
A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form. tRNA Anticodon GGC CGU UGC CCG ACG CGG Amino Acid Proline Alanine Threonine Glycine Cysteine Alanine The dipeptide that will form will be
proline-threonine.
Spliceosomes are composed of _____.
snRNPs and other proteins
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 name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?
translation
