Cell and Molecular Biology: Test 3

Which of the following pairs of codons might you expect to be read by the same tRNA as a result of wobble?

CAC and CAU Not these pairs: AAU and AGU GAU and GAA CUU and UUU

Unlike DNA, which typically forms a helical structure, different molecules of RNA can fold into a variety of three-dimensional shapes. This is largely because ___________________.

RNA is single-stranded.

Transcription in bacteria differs from transcription in a eukaryotic cell because __________________________.

RNA polymerase (along with its sigma subunit) can initiate transcription on its own.

Which of the following statements about prokaryotic mRNA molecules is false?

Ribosomes must bind to the 5′ cap before initiating translation.

DNA polymerases are processive, which means that they remain tightly associated with the template strand while moving rapidly and adding nucleotides to the growing daughter strand. Which piece of the replication machinery accounts for this characteristic?

Sliding-clamp

Which of the following statements is false?

Unlike DNA, RNA uses a uracil base and a deoxyribose sugar.

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking helicase were used to make the cell extracts?

initiation of DNA synthesis

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking the exonuclease activity of DNA polymerase were used to make the cell extracts?

lagging-strand completion

Transcription is similar to DNA replication in that ___________________.

nucleotide polymerization occurs only in the 5′-to-3′ direction.

Indicate whether the following statements are true or false. "DNA replication is a bidirectional process that is initiated at multiple locations along chromosomes in eukaryotic cells."

True

Indicate whether the following statements are true or false. "Meselson and Stahl ruled out the dispersive model for DNA replication."

True

Indicate whether the following statements are true or false. "Primase is needed to initiate DNA replication on both the leading strand and the lagging strand."

True

Which of the following statements about RNA splicing is false?

For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene.

RNA in cells differs from DNA in that ___________________.

it is single-stranded and can fold up into a variety of structures.

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking DNA ligase were used to make the cell extracts?

lagging-strand completion

Which of the following statements correctly explains what it means for DNA replication to be bidirectional?

The replication forks formed at the origin move in opposite directions.

The DNA duplex consists of two long covalent polymers wrapped around each other many times over their entire length. The separation of the DNA strands for replication causes the strands to be "overwound" in front of the replication fork. How does the cell relieve the torsional stress created along the DNA duplex during replication?

Topoisomerases break the covalent bonds of the backbone allowing the local unwinding of DNA ahead of the replication fork.

Which of the following statements is true?

rRNA contains the catalytic activity that joins amino acids together.

The sigma subunit of bacterial RNA polymerase ___________________.

recognizes promoter sites in the DNA.

In eukaryotes, but not in prokaryotes, ribosomes find the start site of translation by ____________________________.

scanning along the mRNA from the 5′ end.

The classic experiments conducted by Meselson and Stahl demonstrated that DNA replication is accomplished by employing a ________________ mechanism.

semiconservative

The process of DNA replication requires that each of the parental DNA strands be used as a ___________________ to produce a duplicate of the opposing strand.

template

How many replication forks are formed when an origin of replication is opened?

2

Which of the following statements about prokaryotic mRNA molecules is true?

A single prokaryotic mRNA molecule can be translated into several proteins. mRNAs are not polyadenylated. Ribosomes can start translating an mRNA molecule before transcription is complete.

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking single-strand binding protein were used to make the cell extracts?

Okazaki fragment synthesis

"Since introns do not contain protein-coding information, they do not have to be removed precisely (meaning, a nucleotide here and there should not matter) from the primary transcript during RNA splicing."

False

Indicate whether the following statements are true or false. "Primase requires a proofreading function that ensures there are no errors in the RNA primers used for DNA replication."

False

Indicate whether the following statements are true or false. "The sliding clamp is loaded once on each DNA strand, where it remains associated until replication is complete."

False

Indicate whether the following statements are true or false. "When DNA is being replicated inside a cell, local heating occurs, allowing the two strands to separate."

False

Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus?

The ribosome binds to the mRNA.

If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes?

Drosophila DNA contains more origins of replication than E. coli DNA.

Which of the following statements about sequence proofreading during DNA replication is false?

The exonuclease activity cleaves DNA in the 5′-to-3′ direction.

Which of the following statements about the genetic code is correct?

The genetic code is redundant (more than one codon per amino acid).

Which of the following might decrease the transcription of only one specific gene in a bacterial cell?

a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site

snRNAs ___________________.

can bind to specific sequences at intron-exon boundaries through complementary base-pairing.

DNA replication is considered semiconservative because ____________________________.

each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand.

What part of the DNA replication process would be most directly affected if a strain of bacteria lacking primase were used to make the cell extracts?

initiation of DNA synthesis