During elongation, which site in the ribosome represents the location where a codon is being read?

1. A site
2. E site
3. P site
4. the small ribosomal subunit

a

Which of the following occurs in prokaryotes but not in eukaryotes?

1. post-transcriptional splicing
2. translation in the absence of a ribosome
3. concurrent transcription and translation
4. gene regulation

c

A nonsense mutation in a gene _____.

1. introduces a premature stop codon into the mRNA
2. has no effect on the amino acid sequence of the encoded protein
3. changes an amino acid in the encoded protein
4. alters the reading frame of the mRNA

a

In the process of transcription, _____.

1. mRNA attaches to ribosomes
2. RNA is synthesized
3. proteins are synthesized
4. DNA is replicated

b

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is _____.

1. TTT
2. AAA
3. UUA
4. UUU

b

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. The dipeptide that will form will be _____.

1. glycine-cysteine
2. cysteine-alanine
3. proline-threonine
4. alanine-alanine

c

Post-translational modifications of proteins may include the _____.

1. addition of carbohydrates to form a glycoprotein
2. addition of a poly-A tail
3. addition of a 5’ cap
4. removal of introns

a

Which one of the following statements about RNA processing is true?

1. A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus.
2. Ribozymes may function in RNA splicing.
3. Exons are cut out before mRNA leaves the nucleus.
4. RNA splicing can be catalyzed by tRNA.

b

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

1. start and stop codons
2. several transcription factors
3. ribosomes and tRNA
4. aminoacyl-tRNA synthetase

b

There are sixty-one mRNA codons that specify an amino acid, but only forty-five tRNAs. This is best explained by the fact that _____.

1. the DNA codes for all sixty-one tRNAs, but some are then destroyed
2. many codons are never used, so the tRNAs that recognize them are dispensable
3. the rules for base pairing between the third base of a codon and tRNA are flexible
4. some tRNAs have anticodons that recognize four or more different codons

c

A mutant bacterial cell has a defective aminoacyl-tRNA synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that _____.

1. proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU
2. the ribosome will skip a codon every time a UUU is encountered
3. none of the proteins in the cell will contain phenylalanine
4. the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons

a

Rank the following one-base point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide.

1. insertion mutation deep within an intron
2. substitution mutation at the third position of an exonic codon
3. substitution mutation at the second position of an exonic codon
4. deletion mutation within the first exon of the gene

1. 4, 3, 2, 1
2. 1, 2, 3, 4
3. 3, 1, 4, 2
4. 2, 1, 4, 3

a

Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression?

1. mRNA, tRNA, and rRNA are transcribed.
2. A cap is added to the 5' end of the mRNA.
3. RNA polymerase requires a primer to elongate the molecule.
4. RNA polymerase binds to the promoter.

b

In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?

1. RNA polymerase II
2. RNA polymerase I
3. RNA polymerase III
4. primase

a

A single base substitution mutation is least likely to be deleterious when the base change results in _____.

1. an amino acid substitution at the active site of an enzyme
2. a stop codon
3. a codon that specifies the same amino acid as the original codon
4. an amino acid substitution that alters the tertiary structure of the protein

c

Which of the following best describes the significance of the TATA box in eukaryotic promoters?

1. It sets the reading frame of the mRNA.
2. Its significance has not yet been determined.
3. It is the recognition site for a specific transcription factor.
4. It is the recognition site for ribosomal binding.

c

Garrod hypothesized that "inborn errors of metabolism" such as alkaptonuria occur because _____.

1. metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies
2. genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes
3. certain metabolic reactions are carried out by ribozymes, and affected individuals lack key splicing factors
4. enzymes are made of DNA, and affected individuals lack DNA polymerase

b

A ribozyme is _____.

1. a catalyst that uses RNA as a substrate
2. an enzyme that catalyzes the association between the large and small ribosomal subunits
3. an enzyme that synthesizes RNA as part of the transcription process
4. an RNA with catalytic activity

d

What type of bonding is responsible for maintaining the shape of the tRNA molecule shown in the figure above?

1. peptide bonding between amino acids
2. hydrogen bonding between base pairs
3. ionic bonding between phosphates
4. van der Waals interactions between hydrogen atoms

b

Alternative RNA splicing _____.

1. can allow the production of proteins of different sizes and functions from a single mRNA
2. increases the rate of transcription
3. can allow the production of similar proteins from different RNAs
4. is a mechanism for increasing the rate of translation

a

The release factor (RF) _____.

1. releases the ribosome from the ER to allow polypeptides into the cytosol
2. binds to the stop codon in the A site in place of a tRNA
3. releases the amino acid from its tRNA to allow the amino acid to form a peptide bond
4. supplies a source of energy for termination of translation

b

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. The anticodon loop of the first tRNA that will complement this mRNA is

1. 3' GGC 5'
2. 3' UGC 5'
3. 5' GGC 3'
4. 5' UGC 3'

a

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in _____.

1. a polypeptide missing an amino acid
2. a base-pair substitution
3. a frameshift mutation
4. a nonsense mutation

a

What must occur before a newly made polypeptide is secreted from a cell?

1. Its signal sequence must target it to the plasma membrane, where it causes exocytosis.
2. Its signal sequence must be cleaved off before the polypeptide can enter the ER.
3. It must be translated by a ribosome that remains free within the cytosol.
4. Its signal sequence must target it to the ER, after which it goes to the Golgi.

d

In eukaryotes there are several different types of RNA polymerase. Which type is involved in transcription of mRNA for a globin protein?

1. RNA polymerase II
2. RNA polymerase I
3. RNA polymerase III
4. primase

a

According to the central dogma, what molecule should go in the blank? DNA → _____ → Proteins

1. tRNA
2. mtDNA
3. rRNA
4. mRNA

d

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

1. start and stop codons
2. several transcription factors
3. ribosomes and tRNA
4. aminoacyl-tRNA synthetase

b

Put the following events of elongation in prokaryotic translation in chronological order.

1. Binding of mRNA with small ribosomal subunit
2. Recognition of initiation codon
3. Complementary base pairing between initiator codon and anticodon of initiator tRNA
4. Base pairing of the mRNA codon following the initiator codon with its complementary tRNA
5. Attachment of the large subunit

1. 1, 2, 3, 5, 4
2. 1, 2, 3, 4, 5
3. 5, 4, 3, 2, 1
4. 2, 1, 4, 3, 5

a

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the _____.

1. binding of ribosomes to mRNA
2. binding of the anticodon to the codon and the attachment of amino acids to tRNAs
3. attachment of amino acids to rRNAs
4. binding of the anticodon to small subunit of the ribosome

b

Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare?

1. Prokaryotic codons usually specify different amino acids than those of eukaryotes.
2. Prokaryotic codons usually contain different bases than those of eukaryotes.
3. Codons are a nearly universal language among all organisms.
4. The translation of codons is mediated by tRNAs in eukaryotes, but translation requires no intermediate molecules such as tRNAs in prokaryotes.

c

Which of the following best describes the significance of the TATA box in eukaryotic promoters?

1. It sets the reading frame of the mRNA.
2. Its significance has not yet been determined.
3. It is the recognition site for a specific transcription factor.
4. It is the recognition site for ribosomal binding.

c

A mutant bacterial cell has a defective aminoacyl-tRNA synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that _____.

1. proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU
2. the ribosome will skip a codon every time a UUU is encountered
3. none of the proteins in the cell will contain phenylalanine
4. the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons

a

The figure above shows a simple metabolic pathway. According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway?

1. 1
2. 2
3. 3
4. It cannot be determined from the pathway.

b

Post-translational modifications of proteins may include the _____.

1. addition of carbohydrates to form a glycoprotein
2. addition of a poly-A tail
3. addition of a 5’ cap
4. removal of introns

a

Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain mutant for the gene-encoding enzyme B would be able to grow on medium supplemented with _____.

1. nutrient A only
2. nutrient B only
3. nutrient C only
4. nutrients A and C

c

An original section of DNA has the base sequence AGCGTTACCGT. A mutation in this DNA strand results in the base sequence AGGCGTTACCGT. This change represents _____.

1. frameshift mutation
2. a silent mutation
3. a point mutation
4. a missense mutation

a

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is _____.

1. 3' UCA 5'
2. 5' TCA 3'
3. 3' ACU 5'
4. 3' UGA 5'

a

A primary transcript in the nucleus of a eukaryotic cell is _____ the functional mRNA, while a primary transcript in a prokaryotic cell is _____ the functional mRNA.

1. the same size as; smaller than
2. the same size as; larger than
3. larger than; the same size as
4. larger than; smaller than

c

Which one of the following, if missing, would usually prevent translation from starting?

1. poly-A tail
2. AUG codon
3. exon
4. 5' cap

b

The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following?

1. The same codons in different organisms translate into different amino acids.
2. A gene from an organism can theoretically be expressed by any other organism.
3. DNA was the first genetic material.
4. Different organisms have different types of amino acids.

b

Which of the following is directly related to a single amino acid?

1. the base sequence of the tRNA
2. the amino acetyl tRNA synthase
3. the complementarity of DNA and RNA
4. the three-base sequence of mRNA

d

Which of the following is the first event to take place in translation in eukaryotes?

1. the small subunit of the ribosome recognizes and attaches to the 5' cap of mRNA
2. covalent bonding between the first two amino acids
3. base pairing of activated methionine-tRNA to AUG of the messenger RNA
4. binding of the larger ribosomal subunit to smaller ribosomal subunits

a

Which of the following statements best describes the termination of transcription in prokaryotes?

1. Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome.
2. RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.
3. RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase.
4. RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA.

b

The figure above 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?

1. GUG
2. GUA
3. UUC
4. UGG

c

Once a peptide has been formed between the amino acid attached to the tRNA in the P site and the amino acid associated with the tRNA in the A site, what occurs next?

1. reading of the next codon of mRNA
2. translocation
3. initiation
4. The codon-anticodon hydrogen bonds holding the tRNA in the A site are broken.

b

Translation requires _____.

1. mRNA, tRNA, and DNA
2. mRNA, tRNA, and rRNA
3. mRNA, tRNA, DNA, and rRNA
4. mRNA, DNA, and rRNA

b

Which of the following statements is true about protein synthesis in prokaryotes?

1. Extensive RNA processing is required before prokaryotic transcripts can be translated.
2. Prokaryotic cells have complicated mechanisms for targeting proteins to the appropriate cellular organelles.
3. Translation can begin while transcription is still in progress.
4. Unlike eukaryotes, prokaryotes require no initiation or elongation factors.

c

How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene, and why?

1. Only a single amino acid could change, because the reading frame is unaffected.
2. It is not possible for a single base substitution to affect protein structure, because each codon is three bases long.
3. The amino acid sequence would be substantially altered, because the reading frame would change with a single base substitution.
4. All amino acids following the substitution would be affected, because the reading frame would be shifted.

a

The tRNA shown in the figure above has its 3' end projecting beyond its 5' end. What will occur at this 3' end?

1. The amino acid binds covalently.
2. The excess nucleotides (ACCA) will be cleaved off at the ribosome.
3. The 5' cap of the mRNA will become covalently bound.
4. The small and large subunits of the ribosome will attach to it.

a

Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain that is mutant for the gene-encoding enzyme A would be able to grow on medium supplemented with _____.

1. nutrient A only
2. nutrient B only
3. nutrient C only
4. nutrients A and C

b

Once researchers identified DNA as the unit of inheritance, they asked how information was transferred from the DNA in the nucleus to the site of protein synthesis in the cytoplasm. What is the mechanism of information transfer in eukaryotes?

1. Messenger RNA is transcribed from a single gene and transfers information from the DNA in the nucleus to the cytoplasm, where protein synthesis takes place.
2. Proteins transfer information from the nucleus to the ribosome, where protein synthesis takes place.
3. Transfer RNA takes information from DNA directly to a ribosome, where protein synthesis takes place.
4. DNA from a single gene is replicated and transferred to the cytoplasm, where it serves as a template for protein synthesis.

a

Transcription in eukaryotes requires which of the following in addition to RNA polymerase?

1. start and stop codons
2. several transcription factors
3. ribosomes and tRNA
4. aminoacyl-tRNA synthetase

b