Biology 12. Protein Synthesis Multiple Choice

What is the effect of a nonsense mutation in a gene? a. It has no effect on the amino acid sequence of the encoded protein. b. It prevents introns from being excised. c. It alters the reading frame of the mRNA. d. It introduces a premature stop codon into the mRNA. e. It changes an amino acid in the encoded protein.

d. It introduces a premature stop codon into the mRNA.

Why might a point mutation in DNA make a difference in the level of protein's activity? a. It might exchange one stop codon for another stop codon. b. It might exchange one serine codon for a different serine codon. c. It might substitute the N terminus of the polypeptide for the C terminus. d. It might substitute an amino acid in the active site. e. It might result in a chromosomal translocation.

d. It might substitute an amino acid in the active site.

Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product? a. a deletion of a codon b. a substitution of the first nucleotide of a GGG codon c. a substitution of the third nucleotide in an ACC codon d. a deletion of 2 nucleotides e. an insertion of a codon

d. a deletion of 2 nucleotides

When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by: a. a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane. b. a signal sequence of RNA that precedes the start codon of the message. c. a specific characteristic of the ribosome itself, which distinguishes free ribosomes from bound ribosomes. d. moving through a specialized channel of the nucleus. e. a chemical signal given off by the ER.

a. a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane.

A mutant bacterial cell has a defective aminoacyl synthetase that attaches the amino acid lysine to tRNAs with the anticodon AAA instead of the amino acid phenylalanine. The consequence of this for the cell will be that: a. proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU. b. none of the proteins in the cell will contain phenylalanine. c. the ribosome will skip a codon every time a UUU is encountered. d. the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons. e. None of the above will occur; the cell will recognize the error and destroy the tRNA.

a. proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is: a. 3' UGA 5'. b. 3' UCA 5'. c. 3'ACU 5'. d. 5' TCA 3'. e. either UCA or TCA, depending on wobble in the first base.

b. 3' UCA 5'.

RNA polymerase moves in which direction along the DNA? a. 3' → 5' along the non-template strand b. 3' → 5' along the template strand c. 5' → 3' along the double-stranded DNA d. 3' → 5' along the non-template strand e. 5' → 3' along the template strand

b. 3' → 5' along the template strand

Which of the following help(s) to stabilize mRNA by inhibiting its degradation? a. tRNA b. 5' cap and poly (A) tail c. TATA box d. introns e. RNA polymerase

b. 5' cap and poly (A) tail

Which of the following nucleotide triplets best represents a codon? a. a triplet separated spatially from other triplets b. a triplet in the same reading frame as an upstream AUG c. a triplet that has no corresponding amino acid d. a triplet at the opposite end of tRNA from the attachment site of the amino acid e. a sequence in tRNA at the 3' end

b. a triplet in the same reading frame as an upstream AUG

In which of the following actions does RNA polymerase differ from DNA polymerase? a. RNA polymerase binds to single-stranded DNA, and DNA polymerase binds to double-stranded DNA. b. RNA polymerase can initiate RNA synthesis, but DNA polymerase requires a primer to initiate DNA synthesis. c. RNA polymerase uses RNA as a template, and DNA polymerase uses a DNA template. d. RNA polymerase does not need to separate the two strands of DNA in order to synthesize an RNA copy, whereas DNA polymerase must unwind the double helix before it can replicate the DNA. e. RNA polymerase is much more accurate than DNA polymerase.

b. RNA polymerase can initiate RNA synthesis, but DNA polymerase requires a primer to initiate DNA synthesis.

A particular triplet of bases in the non-template sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is: a. UUA. b. UUU. c. AAA. d. TTT. e. either UAA or TAA, depending on the first base wobble.

b. UUU.

A frameshift mutation could result from: a. deletion of three consecutive bases. b. either an insertion or deletion of a base. c. a base deletion only. d. a base insertion only. e. a base substitution only.

b. either an insertion or a deletion of a base.

If proteins were composed of only 12 different kinds of amino acids, what would be the smallest possible codon size in a genetic system with four different nucleotides? a. 3 b. 1 c. 2 d. 12 e. 4

c. 2

Which component is not directly involved in translation? a. ribosomes b. mRNA c. DNA d. tRNA e. Amino acids

c. DNA

Which of the following is not true of a codon? a. It may code for the same amino acid as another codon. b. It is the basic unit of the genetic code. c. It extends from one end of a tRNA molecule. d. It consists of three nucleotides. e. It never codes for more than one amino acid.

c. It extends from one end of a tRNA molecule.

Which of the following statements best describes the termination of transcription in prokaryotes? a. RNA polymerase transcribes through an intron and causes the polymerase to let go of the transcript. b. Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome. c. RNA polymerase transcribes through the terminator sequence, causing the polymerase to fall off the DNA and release the transcript. d. RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase. e. RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA.

c. RNA polymerase transcribes through the terminator sequence, causing the polymerase to fall off the DNA and release the transcript.

Alternative RNA splicing: a. increases the rate of transcription. b. is a mechanism for increasing the rate of transcription. c. can allow the production of proteins of different sizes from a single mRNA. d. can allow the production of similar proteins from different RNAs. e. is due to the presence or absence of particular snRNPs.

c. can allow the production of proteins of different sizes from a single mRNA.

Transcription in eukaryotes requires which of the following in addition to RNA polymerase? a. start and stop codons b. aminoacyl synthetase c. several transcription factors (TFs) d. ribosomes and tRNA e. the protein product of the promoter

c. several transcription factors (TFs)

The anticodon of a particular tRNA molecule is: a. changeable, depending on the amino acid that attaches to the tRNA. b. the part of tRNA that bonds to a specific amino acid. c. complementary to the corresponding triplet in rRNA. d. complementary to the corresponding mRNA codon. e. catalytic, making the tRNA a ribozyme.

d. complementary to the corresponding mRNA codon.

What are polyribosomes? a. multiple copies of ribosomes associated with giant chromosomes b. aggregations of vesicles containing ribosomal RNA c. ribosomes containing more than two subunits d. groups of ribosomes reading a single mRNA simultaneously e. ribosomes associated with more than one tRNA

d. groups of ribosomes reading a single mRNA simultaneously

Choose the answer that has these events of protein synthesis in the proper sequence. 1. An aminoacyl-tRNA binds to the A site. 2. A peptide bond forms between the new amino acid and a polypeptide chain. 3. tRNA leaves the P site, and the P site remains vacant. 4. A small ribosomal subunit binds with mRNA. 5. tRNA translocates to the P site. a. 4, 1, 3, 2, 5 b. 5, 4, 3, 2, 1 c. 2, 4, 5, 1, 3 d. 1, 3, 2, 4, 5 e. 4, 1, 2, 5, 3

e. 4, 1, 2, 5, 3

Each of the following options is a modification of the sentence THECATATETHERAT. Which of the following is analogous to a single substitution mutation? a. THECATATTHERAT b. THERATATETHECAT c. CATATETHERAT d. THETACATETHERAT e. THECATARETHERAT

e. THECATARETHERAT

Each of the following options is a modification of the sentence THECATATETHERAT. Which of the following is analogous to a frameshift mutation? a. THERATATETHECAT b. THECATARETHERAT c. CATATETHERAT d. THETACATETHERAT e. THECATATTHERAT

e. THECATATTHERAT

As a ribosome translocates along an mRNA molecule by one codon, which of the following occurs? a. The tRNA that was in the P site moves into the A site. b. The tRNA that was in the A site moves to the E site and is released. c. The tRNA that was in the A site moves to the E site and is released. d. The tRNA that was in the A site departs from the ribosome via a tunnel. e. The tRNA that was in the A site moves into the P site.

e. The tRNA that was in the A site moves into the P site.

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the a. binding of ribosomes to mRNA. b. shape of the A and P sites of ribosomes. c. attachment of amino acids to tRNAs. d. bonding of the anticodon to the codon. e. both C and D

e. both C and D