Deck 11: The Genetic Code

Question 1

The 'one gene-one enzyme' hypothesis is INCORRECT

A) because not all enzymes are produced from just one gene.
B) because genes code for polypeptides.
C) because not all proteins are enzymes.
D) because some proteins are structural.
E) for all of these reasons.

Answer 1

for all of these reasons.

Question 2

The one gene-one polypeptide hypothesis states that

A) each protein produced by a cell is coded for by a single gene.
B) one gene can only possibly produce one protein product.
C) each gene codes for one polypeptide.
D) each cell only has one copy of each gene for each polypeptide.
E) each gene codes for one enzyme which may be composed of polypeptides.

Answer 2

each gene codes for one polypeptide.

Question 3

Gene expression requires that

A) DNA is transcribed into mRNA.
B) mRNA is translated to produce a polypeptide.
C) information coded by DNA is accurately transferred into an amino acid sequence.
D) mRNA is a carrier of the correct information from DNA.
E) All of the answers are correct.

Answer 3

All of the answers are correct.

Question 4

Transcription of RNA from a DNA template is similar to replication of the DNA, in that

A) growth of the synthesised strand occurs in a 3' to 5' direction.
B) the newly synthesised strand is complementary to the template.
C) synthesis is semiconservative.
D) growth of the synthesised strand occurs in a 3' to 5' direction and the newly synthesised strand is complementary to the template.
E) growth of the synthesised strand occurs in a 3' to 5' direction and synthesis is semiconservative.

Question 5

Transcription of RNA from DNA

A) requires a primer.
B) requires DNA polymerase.
C) requires RNA polymerase.
D) requires DNA helicase.
E) begins from the start codon.

Question 6

The three forms of RNA differ in that

A) rRNA is not transcribed from DNA.
B) only mRNA in translated.
C) only mRNA requires a primer for transcription.
D) all tRNAs are identical.
E) both rRNA and tRNA are components of ribosomes, but mRNA is not.

Question 7

Which of the following is a difference in transcription of DNA between prokaryotes and eukaryotes? In prokaryotes

A) translation into polypeptides commences while mRNA is being transcribed.
B) there is only one type of RNA polymerase.
C) transcript mRNAs are polycistronic.
D) transcript mRNAs undergo processing after translation.
E) All of the answers are differences.

Question 8

Initial transcription of the DNA template in eukaryotes

A) only transcribes the exons.
B) is mediated by DNA polymerase.
C) is mediated by RNA polymerase.
D) occurs in the ribosomes.
E) requires a primer.

Question 9

Which of the following statements about post-transcription processing of mRNA in eukaryotes is CORRECT?

A) snRNPs act to remove exons from RNA.
B) Splicing may take place to remove introns.
C) The promoter is found adjacent to the poly-A site.
D) All mRNA primary transcripts self-fold to facilitate splicing.
E) processing of mRNA occurs in the cytoplasm of the cell.

Question 10

During post-transcription processing of mRNA in eukaryotes

A) the primary transcript is 'capped' by the addition of a modified guanosine triphosphate residue to the 5' end.
B) the primary transcript is 'capped' by the addition of a modified guanosine triphosphate residue to the 3' end.
C) the promoter sequence is removed from the 5' end of the mRNA and a modified guanosine tri phosphate is added to the 3' end.
D) the 5' end of the transcript is cleaved, and a poly A 'tail' is added to the new 5' end.
E) the primary transcript is 'capped' by the addition of a modified guanosine triphosphate residue to the 3' end and the promoter sequence is removed from the 5' end of the mRNA and a modified guanosine tri phosphate is added to the 3' end.

Question 11

Which of the following is a specific sequence that binds RNA polymerase?

A) A reading frame
B) An operon
C) A transcription unit
D) A promoter
E) An intron

Question 12

In eukaryotes, transcription of chromosomal DNA

A) occurs in the ribosome.
B) involves three different RNA polymerases.
C) is initiated by a primer.
D) starts at the origin.
E) is synthesised in the 3' to 5' direction.

Question 13

The genetic code is described as unambiguous because

A) each amino acid is specified by only one codon.
B) each codon specifies only one amino acid.
C) each protein is initiated by a specific promoter.
D) AUG is always the START codon.
E) one gene always equals one protein.

Question 14

An example of a frameshift mutation is when

A) a nucleotide is added to an ORF resulting in a nonsense mutation.
B) a nucleotide is lost from an ORF resulting in a nonsense mutation.
C) an altered protein is produced as a result of a missense mutation.
D) two nucleotides are added to an ORF changing the function of the protein product.
E) All of the answers are correct.

Question 15

An mRNA 2650 base pairs long was transcribed from a gene containing 3782 base pairs. The most likely explanation would be that

A) the gene sequence was altered and now contains a nonsense mutation.
B) the gene sequence was altered and now contains a missense mutation.
C) splicing during transcription removed introns from the sequence.
D) the gene sequence was altered and now contains a nonsense mutation and splicing during transcription removed introns from the sequence.
E) the gene sequence was altered and now contains a missense mutation and splicing during transcription removed introns from the sequence.

Question 16

Which of the following statements about the genetic code is the most CORRECT?

A) Protists use a simplified genetic code.
B) Genetic codes are similar in most living organisms.
C) Plants and animals have markedly different genetic codes.
D) Each amino acid has a unique genetic code.
E) All organisms originated with the same genetic code but genetic drift has introduced variation.

Question 17

In RNA translation

A) codons are read from the 5' end.
B) codons are read from the 3' end.
C) the first codon in the sequence is UAG.
D) silent letters punctuate the codons.
E) codons are read from the C terminal to the N terminal.

Question 18

Most eukaryotes use an open reading frame in gene expression. This means that

A) only one protein can be encoded from the same region of DNA.
B) protein synthesis begins with the assembly of an initiation complex.
C) all protein sequences start with the same amino acid.
D) different proteins can be encoded from each of the complementary strands of DNA.
E) many amino acids are coded for by synonymous codons.

Question 19

Which of the following statements about RNA is CORRECT?

A) Eukaryote mRNA molecules are longer than prokaryote mRNAs.
B) Amino acids link to the 5' end of the tRNA.
C) Eukaryote mRNA molecules are polycistronic.
D) tRNA is activated by aminoacylation.
E) mRNA translation is initiated by binding the mRNA to tRNA.

Question 20

tRNA molecules

A) transfer proteins out of the cytoplasm.
B) covalently bond to amino acids.
C) transfer information between DNA and the ribosomes.
D) covalently bond to nucleotides of mRNA.
E) bind to the growing polypeptide chain.

Question 21

The elongation phase of polypeptide assembly is a repetitive process that includes the

A) formation of sequential peptide bonds.
B) catalysis of peptide bond formation by peptidyl transferase.
C) translocation of a tRNA molecule from the A site to the P site after peptide bond formation.
D) recognition of the codon in the mRNA by the specific tRNA by complementary base pairing.
E) All of the answers are correct.

Question 22

The formation of the initiation complex in protein synthesis does NOT involve

A) one small and one large ribosomal subunit.
B) binding of an uncharged tRNA at the initiation codon.
C) N-formyl methionine-charged tRNA.
D) a set of initiator proteins.
E) the formation of two tRNA binding sites.

Question 23

A cell lacking peptidyl transferase would NOT be able to make proteins because

A) N-formyl methionine-charged tRNA would not bind to the initiator codon.
B) peptide bonds between the carboxyl group of the incoming amino acid to the amino group of the growing polypeptide chain would not be catalysed.
C) peptide bonds between the amino group of the incoming amino acid to the carboxyl group of the growing polypeptide chain would not be catalysed.
D) the termination codon would not be recognised.
E) the growing peptide would not interact with the specific tRNA.

Question 24

During protein synthesis, the mRNA

A) fits into a groove formed between the large and small ribosomal subunits.
B) is exposed to the A and P sites.
C) is bound underneath the small ribosomal subunit, allowing tRNAs access to the codons.
D) fits into a groove formed between the large and small ribosomal units and is exposed to the A and P sites.
E) is exposed to the A and P sites and is bound underneath the small ribosomal subunit, allowing tRNAs access to the codons.

Question 25

The translocation reaction involves

A) the transfer of the growing peptide chain from the P site to the single amino acid on the tRNA in the A site.
B) the displacement of the uncharged tRNA from the P site into the cytosol.
C) the movement of the ribosome three bases along the mRNA in the 5' to 3' direction.
D) the binding of the next aminoacyl-tRNA to the vacant A site.
E) All of the answers are correct.

Question 26

Which of the following is NOT involved in the termination of protein synthesis?

A) A stop tRNA binds to the A site.
B) The aminoacyl bond between the polypeptide chain and the peptidyl-tRNA in the P site is hydrolysed by termination factors.
C) The arrival of a stop codon on the mRNA.
D) An empty P site causes the ribosome to dissociate from the mRNA.
E) The small and large ribosome subunits dissociate from each other and are recycled for future protein synthesis.

Question 27

Proteins found in the nucleus of a eukaryotic cell

A) were assembled there.
B) diffused through the nuclear pores from the cytosol.
C) are the same as the proteins found in the cytosol.
D) are synthesised in the nucleus.
E) are actively transported into the nucleus.

Question 28

Signal sequences

A) tell the cell that a protein needs to be modified before it is functional.
B) are recognised and bound by specific receptors at the correct cellular site for the polypeptide.
C) are never removed because they are a part of the final, functional protein.
D) tell the ribosome where to start and stop translation.
E) are added after protein synthesis.

Question 29

Splicing is

A) the processing of a primary mRNA transcript to remove introns.
B) the processing of a primary mRNA transcript to remove exons.
C) the DNA directed copying of an open reading frame to produce an mRNA.
D) the translocation of the mature mRNA from the nucleus to the cytoplasm for protein synthesis.
E) the process by which the open reading frame of a gene is transcribed into an mRNA.

Question 30

The process by which an mRNA species is converted to a protein is called

A) complementarity.
B) elongation.
C) gene transfer.
D) translation.
E) transcription.

Question 31

A transcription unit is

A) the gene being transcribed.
B) the region of DNA between the promoter and the termination sequence of a gene.
C) the final mRNA species exported from the nucleus for protein production.
D) the region where the transcription factor binds to initiate transcription.
E) the open reading frame of a gene.

Question 32

In eukaryotic cells, transcription generates

A) mRNA.
B) ribosome subunits.
C) complementary DNA.
D) 3 forms of RNA.
E) aminoacyl-tRNA.

Question 33

Double-stranded regions of RNA

A) are not as stable as double-stranded DNA.
B) unlike DNA, hydrogen bond in parallel strands.
C) can form between two complementary regions within one molecule of RNA.
D) do not occur.
E) are frequently observed in isolated RNA, but probably do not occur in cells.

Question 34

Protein synthesis differs between prokaryotes and eukaryotes. Which of the following statements about these differences is INCORRECT?

A) Many bacterial mRNA transcripts contain more than one polypeptide coding region while eukaryotic mRNAs usually code for only one protein.
B) Prokaryotic mRNA is translated while being transcribed; eukaryotic mRNA requires processing before translation.
C) Eukaryotic mRNA when transcribed contains long sequences of nucleotides that are not translated; in prokaryotes all the transcribed mRNA is translated.
D) Many antibiotics specifically target bacterial protein synthesis, but have no effect on eukaryote protein synthesis.
E) Prokaryotic ribosomes attach to the mRNA during translation and so do not require the A site for aminoacyl-tRNA binding as is present on the ribosome of eukaryotic cells.

Question 35

Why is there NOT a one-to-one correlation between the genetic code and amino acids?

A) Because there are 20 amino acids but only 4 nucleotide bases.
B) Because the genetic code includes uracil in mRNA.
C) Because not all proteins contain all amino acids.
D) Because unlike DNA, there are not equal proportions of some amino acids to others.
E) Because transcription occurs inside the nucleus, whereas translation occurs in the cytoplasm.

Question 36

Which of the following statements in relation to signal sequences is INCORRECT?

A) The signal sequence binds the Signal Recognition Protein.
B) The bound signal sequence docks with the rough endoplasmic reticulum.
C) Signal sequences are at the C-terminus end of a protein.
D) Signal sequences are short (5-30aa) peptides.
E) A signal sequence embedded in the rough endoplasmic reticulum is not always cleaved from a synthesised protein.

Question 37

You are working with a strain of the common laboratory organism Pichia pastoris, a unicellular yeast. You note that this particular strain will not grow on media when it lacks valine. However, when you provide the yeast with threonine-ammonia lyase, the first enzyme in the valine biosynthesis pathway, it grows on media lacking valine. This suggests that

A) valine is not an essential amino acid for Pichia pastoris.
B) there is a mutation in the gene encoding threonine-ammonia lyase in the yeast.
C) there is a mutation in the last step of the valine biosynthesis pathways.
D) there is a mutation in a middle step of the valine biosynthesis pathways.
E) there is a mutation in the valine biosynthesis pathway but it is not possible to say where.

Question 38

The central dogma of gene expression can be summarised as

A) DNA $\rightarrow$ RNA $\rightarrow$ Protein.
B) RNA $\rightarrow$ DNA $\rightarrow$ Protein.
C) Protein $\rightarrow$ DNA $\rightarrow$ RNA.
D) DNA $\rightarrow$ Protein $\rightarrow$ RNA.
E) RNA $\rightarrow$ Protein $\rightarrow$ DNA.

Question 39

A DNA strand has the sequence of GCC CGG TAT TAA. What is the complimentary RNA transcript?

A) GCC CGG TAT TAA.
B) CGG GCC UTU TUU.
C) CGG GCC ATA ATT.
D) CGG GCC AUA AUU.
E) GCC CGG TUT TUU.

Question 40

A polycistronic unit is

A) a eukaryotic transcription unit that encodes for more than one protein.
B) a bacterial transcription unit that encodes for more than one protein.
C) a bacterial or eukaryotic transcription unit that encodes for more than one protein.
D) comprised of mRNA coding regions immediately adjacent to each other.
E) a viral transcription unit that encodes for more than one protein.

Question 41

A section of coding sequence of DNA is comprised of 27 bases. How many amino acids would this be translated into?

A) 27
B) 13
C) 14
D) 54
E) 9

Question 42

Two synonymous codons are specific for histidine. If the last base of one of these codons was changed to a different nucleotide, what could be the outcome?

A) There would be a frameshift mutation.
B) The codon would specify an amino acid other than histidine.
C) Because of degeneracy, the codon would still specify for histidine.
D) The codon could still be specific for histidine, or it could be specific for a different amino acid.
E) It would result in a 'nonsense' codon that did not specify any amino acid.

Question 43

In prokaryotes, the first amino acid in protein synthesis is always

A) methionine.
B) N-formyl methionine.
C) an acidic amino acid.
D) the first amino acid of the signal sequence.
E) L-methionine.