Practice Exam 4

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

2

Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. All intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined.

45 minutes

A sample of double-stranded DNA contains 42% cytosine. Approximately what percent of the nucleotides in this sample will be thymine?

8%

Hershey and Chase set out to determine which type of molecule is used for genetic inheritance. They completed a series of experiments where E. coli was infected by a T2 virus. Which molecular component of the T2 virus ended up inside the cell?

DNA

After DNA replication, the resulting daughter DNA double helix contains one strand of the original parental DNA and one new strand. What is the explanation for this phenomenon?

DNA replication is semiconservative.

Much of the human genome does not code for proteins. Which of the following types of DNA are found in these regions of the genome?

DNA that is transcribed into several kinds of small RNAs with biological function

Which of the following statements correctly describes the structure of chromatin?

Heterochromatin is highly condensed, whereas euchromatin is less compact.

Which of the three types of viruses shown would you expect to have glycoproteins among its components?

III only

Which of the following statements describes the effect of a nonsense mutation on a gene?

It introduces a premature stop codon into the mRNA.

Which of the following statements correctly describes a ribozyme?

It is an RNA with catalytic activity.

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

It is the recognition site for the binding of a specific transcription factor.

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

In E. coli, a mutation in a gene called dnaB prevents the helicase from binding at the origin of replication. Which of the following events would you expect to occur as a result of this mutation?

No replication fork will be formed.

Which of the following descriptions correctly identifies a main structural difference between viruses with envelopes and viruses without envelopes?

Only viruses with envelopes have their contents enclosed by a layer containing lipids

Which of the following statements accurately describes differences between DNA replication in prokaryotes and DNA replication in eukaryotes?

Prokaryotic chromosomes have a single origin of replication, whereas eukaryotic chromosomes have many.

Which of the following processes destroys RNA molecules if they have a sequence complementary to an introduced double-stranded RNA?

RNA interference

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.

Which of the following responses explain why the apparent high rate of mutation in RNA viruses?

RNA virus genome replication does not involve proofreading.

Which of the following statements about RNA processing is correct?

Ribozymes may function in RNA splicing.

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. Which of the following best explains the effect of telomerase on cellular aging?

Telomerase can eliminate telomere shortening and slows aging.

In 2009, a flu pandemic was believed to have originated when viral transmission occurred from pig to human, thereby earning the designation "swine flu." Although pigs are thought to have been the host for the 2009 virus, sequences from bird, pig, and human viruses were all found within this newly identified virus. What is the most likely explanation for the presence of sequences from bird, pig, and human viruses?

The RNA of related viruses can reassort during viral assembly resulting in new genetic combinations.

A cell is considered to be differentiated if it has which of the following characteristics?

The cell produces proteins specific to a particular cell type.

Which of the following characteristics is typical of the lytic cycle of a bacteriophage?

The host membrane ruptures, releasing many phages.

Which of the following statements correctly describes the difference between the leading and the lagging strands of DNA in DNA replication?

The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

Which of the following best explains the observation that in bacteria, there are 61 mRNA codons that specify an amino acid, but only 45 tRNAs?

The rules for base pairing between the third base of a codon and tRNA are flexible.

Cytoplasmic determinants are best described as having which of the following characteristics?

They are maternal substances in the egg that influence the course of early development.

Which of the following statements correctly describes a characteristic of tumor-suppressor genes?

They encode proteins that help prevent uncontrolled cell growth.

Which of the following characteristics correctly describes retroviruses?

They have a single-stranded RNA that acts as a template for DNA synthesis.

Which of the following describes the role typical proto-oncogenes have when they are expressed in cells that are not cancerous?

They stimulate normal cell growth and division.

Which of the following methods would be best to use for distinguishing between an infectious agent that is a virus and one that is a prion?

Treat the substance with enzymes that destroy all nucleic acids, and then determine whether the substance is still infectious.

If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins during processing in the Golgi apparatus, which of the following processes is most likely to occur?

Viruses released by that cell would have a decreased ability to infect cells than the virus that originally infected the cell.

A single base substitution mutation is likely to have a less harmful effect when the base change results in which of the following?

a codon that specifies the same amino acid as the original codon

If a mutation deactivated a regulatory gene of a repressible operon in an E. coli cell which of the following describes the most likely outcome?

continuous transcription of the structural gene controlled by that regulator

Which of the following is a molecule that helps to "turn off" the expression of genes in a cell?

corepressor

Which of the following results is most likely to occur if acetylation of histone tails in the chromatin of embryonic cells is increased?

decreased chromatin condensation

DNA methylation and histone acetylation are examples of which of the following processes?

epigenetic phenomena

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

hydrogen bonding between base pairs

Which list the provides the correct enzyme order required for nucleotide excision repair of a thymine dimer?

nuclease, DNA polymerase, DNA ligase

Which of the following is most likely to result if a cell is unable to produce histone proteins?

the cell's DNA could not be packed into its nucleus

The host range of a virus is determined by whether ________.

the proteins on virus surface can bind with proteins on the host surface