Mastering Biology Chapter 17
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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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'.
RNA polymerase moves in which direction along the DNA?
3' to 5' along the template strand
During RNA processing a(n) _____ is added to the 3' end of the RNA.
5' untranslated region A poly-A tail is added to the 3' end of the RNA.
Which of the following statements about mutations is false?
A knock-out mutation results in a total absence of the mutated protein. A knock-out mutation refers to the loss of a protein's function but not necessarily to its complete absence.
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 This is the site at which new aminoacyl tRNAs that are complementary to the mRNA codon enter the ribosome.
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. If the mutations occur within the same codon, only that codon (amino acid) will be altered.
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.
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 Transcription involves the formation of an RNA strand that is complementary to the DNA template strand.
Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?
Complementary Because the template strand determines the nucleotides to be added to the RNA strand, using the same complementarity rules of the DNA, they will be complementary to each other.
If a DNA sequence is altered from TAGCTGA to TAGTGA, what kind of mutation has occurred?
Deletion The original sequence has lost the base C.
Which one of the following is true of tRNAs?
Each tRNA binds a particular amino acid. Aminoacyl-tRNA synthetase joins a specific amino acid to a tRNA, a single strand of RNA about 80 nucleotides long.
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 is the effect of a nonsense mutation in a gene?
It introduces a premature stop codon into the mRNA.
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. The enzyme is free to transcribe other genes in the cell.
Where does RNA polymerase begin transcribing a gene into mRNA?
It starts after a certain nucleotide sequence called a promoter. In both eukaryotes and prokaryotes, RNA polymerase binds to the gene's promoter and begins transcription at a nucleotide known as the start point, although in eukaryotes the binding of RNA polymerase to the promoter requires transcription factors.
What is the function of RNA polymerase?
It unwinds the double helix and adds nucleotides to a growing strand of RNA. RNA polymerase has several functions in transcription, including unwinding the DNA double helix and adding RNA nucleotides.
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. This combination results in no net change in the number of bases, so the reading frame would eventually be restored.
DNA does not store the information to synthesize which of the following?
Organelles Synthesis of organelles is not directly coded in the DNA.
Which of the following processes is an example of a post-translational modification?
Phosphorylation Enzymes can phosphorylate proteins to alter their activity.
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.
What name is given to the process in which pre-mRNA is edited into mRNA?
RNA processing RNA processing edits the RNA transcript that has been assembled along a DNA template.
Where does translation take place?
Ribosome Translation, or protein synthesis, occurs at the ribosome.
Which of the following steps occurs last in the initiation phase of translation?
The large ribosomal subunit joins the complex. This step occurs after the 5' mRNA is bound by the ribosome and the start codon is bound by an aminoacyl tRNA.
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.
What is meant by translocation?
The ribosome slides one codon down the mRNA. Translocation is the process by which the ribosome slides down the mRNA so a new cycle of elongation can begin.
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. All of these processes occur at the initiation of translation.
What is the process called that converts the genetic information stored in DNA to an RNA copy?
Transcription DNA is transcribed to give an RNA copy.
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. The second and third codons in the new sequence are different from the original codons.
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
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 A number of examples of biological catalysts containing RNA have been discovered, including ribozymes, snRNAs, and ribosomes themselves.
What does a mutagen cause?
a change in the sequence of DNA Mutations are changes in the genetic material of the cell.
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 A frameshift mutation at the beginning of a gene would affect every codon after the point where the mutation occurred. During protein synthesis, incorrect amino acids would be inserted from the point where the frameshift mutation occurred on; the resulting protein would most probably be nonfunctional. For this reason, a frameshift mutation at the beginning of a gene is generally the most severe type of mutation.
Polypeptides are assembled from _____.
amino acids Proteins are composed of amino acid monomers.
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
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 Ribosomes, the sites of translation, are found in the cytoplasm.
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 Exons are expressed regions.
What type of bonding is responsible for maintaining the shape of the tRNA molecule?
hydrogen bonding between base pairs
RNA processing converts the RNA transcript into _____.
mRNA The editing of the RNA transcript produces mRNA.
Which nucleic acid is translated to make a protein?
mRNA mRNA is the message that is translated to make a protein.
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 The 5' cap consists of a 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 These are the component of spliceosomes.
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.
A codon consists of _____ bases and specifies which _____ will be inserted into the polypeptide chain.
three ... amino acid Three nucleotide bases make up a codon and specify which amino acid comes next in the sequence.
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 Transcription is the process by which a DNA template is used for the manufacture of several different types of RNA.
What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?
translation Translation is the process by which information encoded in RNA is used to manufacture a polypeptide.