Mastering- Assignment 8

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Which enzyme breaks the hydrogen bonds during replication?

DNA helicase

How do stabilizing proteins work on the DNA?

They bind to the single-stranded DNA.

In which direction does the replication fork move?

It moves ahead of the newly synthesized DNA.

What ensures that the single strands of DNA do not come back together?

Stabilizing proteins

What are the products of semiconservative replication for a double-stranded DNA molecule?

Two double-stranded DNA molecules, each consisting of one parental strand and one daughter strand.

Why is DNA replication essential for a cell?

An organism must copy its DNA to pass genetic information to its offspring.

What is the function of the parental DNA in replication?

It serves as the template for DNA replication.

Why must primase be used before DNA polymerase when replicating DNA?

Primase provides an RNA primer with a 3′ end on which DNA polymerase can act

Which enzyme joins the gaps between synthesized DNA fragments of the lagging strand?

DNA ligase

What nucleotides would DNA polymerase add if it encountered the nucleotide sequence: ATTGC?


Which strand will require more RNA primers to complete synthesis?

Lagging strand

In which direction does DNA polymerase synthesize DNA for the lagging strand?

5′ to 3′

What characteristic of DNA allows two connected DNA polymerases to synthesize both the leading and lagging strands?

DNA is flexible.

What is the function of the connector proteins?

They link the leading strand DNA polymerase and the lagging strand DNA polymerase together.

Which DNA strand is synthesized continuously?

Leading strand

Which of the following are terms associated with Okazaki fragments?

Lagging strand, DNA ligase, and discontinuous

Why is the DNA synthesis of the lagging strand considered discontinuous?

The synthesis is moving in the opposite direction from the replication fork.

Transcription produces which of the following?

mRNA, tRNA, and rRNA are all produced by transcription.

According to the animation, which of the following makes mRNA from the information stored in a DNA template?

RNA polymerase

Ribosomes contain which of the following?


Which of the following is involved in bringing amino acids to the ribosomes?


Which of the following can be translated into protein?


What is the initial target of RNA polymerase?

The promoter

RNA polymerase is guided by the

template strand of DNA.

RNA that has hydrogen bonded to itself forms a

stem loop.

How would one increase the concentration of a particular polypeptide in a cell?

Increase the level of transcription

During elongation, how is the RNA synthesized?

5′ to 3′

What results from the process of translation?

A polypeptide

How is bacterial translation different from eukaryotic translation?

Bacteria can begin translation before transcription has terminated.

According to the animation, ribosomes move along the mRNA in which direction?

5′ to 3′

As shown in the animation, the start codon also codes for which amino acid?


How many codons code for the amino acid arginine?


GAU codes for

aspartic acid.

Which of the following amino acids is coded by only one codon?


What would happen if the DNA sequence that coded for Cys was mutated in the third position from a U to an A?

A stop codon would be introduced prematurely.

During the initiation step of translation, the fMet charged tRNA assembles in which site of the ribosome?

P site

How does the ribosome know if the entering charged tRNA is correct?

The anticodon on the tRNA base pairs to the codon on the mRNA.

Where would one find an uncharged tRNA molecule in a ribosome?

In the P and E sites

What kind of bond is formed when two amino acids join together?

A peptide bond

How is translation terminated?

When a protein called a release factor enters and binds to the A site

What is the inducer molecule in the lac operon?


With which genetic region does the repressor protein interact?

The operator region

When the cell is not in the presence of lactose,

the repressor proteins bind to the operator

What is the basic function of the lac operon?

To code for enzymes involved in catabolizing lactose.

According to the animation, to what genetic element does the RNA polymerase bind?

The promoter

Which of the following genetic elements is transcribed into a single mRNA?

The structural genes

Which operons are always transcribed unless deactivated?

Repressible operons

Which operons are never transcribed unless activated?

Inducible operons

According to the animation, where on the DNA strand does a repressor bind?

The operator

When the cell is NOT in the presence of tryptophan

RNA polymerase can transcribe mRNA.

When is the repressor protein transcribed?

It is always transcribed

Why is the tryptophan operon turned off in the presence of tryptophan?

Tryptophan binds to and activates the repressor proteins; the repressor proteins, in turn, bind to the operator, preventing transcription.

What is the overall function of the trp operon?

To ensure that the cell has a supply of tryptophan at all times

According to the animation, how do the repressor proteins block the transcription of the structural genes?

It binds to the operator when activated.

Thymine dimers result from

nonionizing radiation.

Which of the following might result in a frameshift mutation?


Which of the following describes how 5-bromouracil might create a mutation?

It can replace the base thymine, and can base pair with guanine rather than adenine.


increase the likelihood of mutations in DNA.

A nucleotide-altering chemical

can alter nitrogenous bases of DNA, resulting in incorrect base pairing.

How is DNA methylation used in DNA repair?

The mismatch-repair enzymes can use a lack of methylation to identify and remove newly synthesized DNA.

Which of the following repair enzymes cannot repair thymine dimers?

Mismatch-repair enzymes

Why is light required for photolyases?

The light provides the energy to break the bonds between the thymine dimers.

Which of the following repair mechanism(s) does not involve DNA polymerase?

Light-repair mechanism

What is considered to be the average natural mutation rate that occurs during DNA replication?

One in every billion nucleotides replicated.

A mutation that affects the genotype of the organism but not the phenotype is called a

silent mutation.

A base insertion or deletion in the translated region of the gene may lead to

frameshift mutation.

A base substitution that changes a codon coding for an amino acid to a stop codon is called a

nonsense mutation.

How frequently do silent mutations occur?

One out of every three mutations

A silent mutation is so named because

it has no effect on the overall amino acid sequence

A new chemotherapeutic agent is developed that alters the structure of all thymines in DNA. These thymines are then misread during the production of mRNA. Which of the following could NOT result from this type of mutation?

frameshift mutation

While studying protein synthesis in the lab, you experimentally induce a mutation in a bacterium’s DNA. You assess the proteins in the mutated bacterium and find that one of them is significantly shorter than its wild-type counterpart. Based on this information, what type of mutation did you induce?

nonsense mutation

A student states that the trp gene is located at 26 minutes. What does this mean?

It takes 26 minutes for the gene to be transferred during conjugation

If argG, argR, and argE are all required to make a cell able to metabolize arginine, how long would it take for an arg- recipient to become arg+?

87 minutes

If conjugation was allowed to be carried out for 25 minutes, which genes would be transferred to the recipient strain?


How does conjugation help geneticists map the genomes of bacteria?

It provides them with the relative positions of the genes on the chromosomes.

If gene X transferred at 99 minutes for E. coli, what conclusion could you make about gene X?

Gene X is close to the fertility factor on the Hfr chromosome, but is near the end of the chromosome transfer

What is the function of the conjugation pilus?

It pulls the F+ and F- cells together.

What is required by an F- cell to become an F+ cell?

F plasmid

What is the key difference between donor cells and recipient cells?

An F plasmid

What cellular macromolecule is the fertility factor comprised of?

Nucleic acid

At which point does a recipient cell become an F+ cell?
1.Fusion of the cell membranes
2.Attachment of the sex pilus
3.Transfer of the single stranded F factor
4.Pulling of donor and recipient cells together
5.Formation of the complementary strand of the F factor


How does an F+ cell differ from an Hfr cell?

Hfr strains have the F plasmid integrated into the chromosome.

Why does conjugation between an Hfr strain and an F- strain not result in two Hfr strains?

Conjugation is typically disrupted before the fertility factor can be transferred

Which of the following is a characteristic of an F+ cell?

Ability to synthesize sex pili, presence of a fertility factor, and ability to mate with an F- cell.

What benefit does the F- strain receive from mating with an Hfr strain?

It acquires new, potentially beneficial genes from the Hfr strain.

Bacterial conjugation is often referred to as bacterial sex. Why is this term inaccurate?

Conjugation does not result in the formation of new offspring.

What must occur for bacterial conjugation to take place?

The cells must come into contact with each other.

Which statement about conjugation is false?

Conjugation is a process of bacterial reproduction

Based on the animation, what is transferred during bacterial conjugation?

A bacterial plasmid

A recombinant cell

is a cell that receives DNA from an outside source and incorporates it into its own.

What is the hallmark of all horizontal gene transfers?

Transfer of DNA between organisms of the same generation

Which of the following is an example of horizontal gene transfer in bacteria?

Transduction, conjugation, and transformation

What is unique about transduction compared to normal bacteriophage infection?

Transduction transfers DNA from the chromosome of one cell to another.

How is generalized transduction different from specialized transduction

Generalized transduction is initiated during lytic cycle of a virulent bacteriophage; specialized transduction is initiated during the lysogenic cycle of a temperate bacteriophage.

A transducing phage

contains fragments of the host chromosome instead of the viral genome

When a transducing phage interacts with a new host cell,

the DNA from the previous host can recombine with the new host chromosome.

Competent cells are cells that

can take up DNA from their surrounding environment and integrate it into their own chromosomes by recombination.

Mice that are injected with only the R strain of Streptococcus pneumoniae

stay healthy, because their immune systems can kill this strain easily.

What characteristic of the S strain allows it to evade the immune system of the mice?

The cells have a capsule.

What most likely explains the recovery of live S strain cells from a mouse injected with heat-killed S strain mixed with live R strain cells?

The R strain picked up the S strain DNA, enabling it to produce a capsule

Which finding is most surprising from Griffith’s experiments?

S strain cells are isolated from the blood of mice infected with heat-killed S strains and live R strains.

How is a complex transposon different from a simple transposon?

They have two simple transposons with another DNA sequence between them

Why does a complex transposon often contain an extra piece of DNA between the two insertion elements?

It is often a gene that confers a survival advantage to the host, such as antibiotic resistance.

How would you be able to determine if the Tn5 transposon you put into a bacterium integrated into the host genome?

If the Tn5 transposon integrated into the host genome, the cells would show resistance to the antibiotic kanamycin.

Insertion sequences target which areas on a target DNA sequence?

A sequence of nucleotides identical to the inverted repeat sequence found on the insertion sequence itself

What makes an insertion sequence different from other DNA sequences found in a cell?

They are capable of effecting their own movement from one location to another on DNA.

If the gene that codes for transposase is mutated so that it no longer produces the fully functional enzyme, how will the insertion sequence be affected?

The insertion sequence would lose its ability to effect its own movement.

How does replicative transposition differ from cut-and-paste transposition?

Replicative transposition results in the transposon being copied to a new location; in cut-and-paste transposition, the entire transposon moves to the new location.

Which type of transposon would contain a gene for transposase?

Both simple and complex transposons

How do complex transposons differ from simple transposons?

Complex transposons code for additional genetic elements, such as antibiotic resistance genes; simple transposons only code for the transposase gene essential for the tranposon itself.

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