Question 1

Enzymes that remain bound to their nascent chains through many polymerization steps are said to be .

Accepted Answer

Enzymes that remain bound to their nascent chains through many polymerization steps are referred to as processive enzymes. This is because they continue to catalyze the formation of multiple peptide bonds without dissociating from the growing polypeptide chain. Constitutive enzymes are those that are always present and active in a cell or organism, while distributive enzymes catalyze a single reaction per molecular encounter. Conjugated enzymes are those that contain non-protein components necessary for their function.

Question 2

E. coli DNA polymerase catalyzes polymerization in the directions).

Accepted Answer

E. coli DNA polymerase catalyzes polymerization in the 5ʹ → 3ʹ direction. This is the direction in which new DNA strands are synthesized, with the addition of nucleotides to the 3ʹ end of the growing chain. E. coli DNA polymerase cannot operate in the opposite 3ʹ → 5ʹ direction, as this would involve breaking the phosphodiester bonds between nucleotides in the existing template strand, which requires different enzymes.

Question 3

Which DNA polymerase is most responsible for chain elongation in E. coli?

Accepted Answer

DNA polymerase III is the main replicative polymerase in E. coli and is responsible for the bulk of chain elongation during DNA replication. DNA polymerase I is involved in removing RNA primers and filling in gaps, while DNA polymerase II and IV are involved in DNA repair and replication under certain conditions.

Question 4

The protein machine that carries out DNA replication is called .

Accepted Answer

The replisome is the complex of proteins that carries out DNA replication, including the DNA polymerase that synthesizes new DNA strands and other enzymes and proteins involved in the process. The replication fork is the structure formed during DNA replication where the two strands of DNA are unwound and the new strands are synthesized. The Klenow fragment is a portion of DNA polymerase I that has been widely used in molecular biology for in vitro DNA synthesis and modification, but is not the name of the protein machine that carries out DNA replication. Therefore, the best choice is D) the replisome.

Question 5

Nick translation is a process for

Accepted Answer

The answer of Nick translation is a process for
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Question 6

Approximately base pairs are added per second during DNA in vivo replication in E. coli.

Accepted Answer

The rate of DNA replication in E.coli is approximately 1000 base pairs per second. This is a relatively fast rate compared to the rate of DNA replication in eukaryotic cells, which is only about 50 base pairs per second. The high rate of DNA replication in E.coli is due to the efficient replication machinery present in this bacterial species.

Question 7

Polymerization of the lagging strand is catalyzed by .

Accepted Answer

Polymerization of the lagging strand is catalyzed by a second core complex on the same polymerase holoenzyme that polymerizes the leading strand. The leading and lagging strands are synthesized simultaneously by the same replisome, but in opposite directions. The leading strand is continuously synthesized in the 5' to 3' direction, while the lagging strand is synthesized discontinuously in the opposite direction, creating short Okazaki fragments that must be joined together by DNA ligase. This process is coordinated by the second core complex on the same polymerase holoenzyme that polymerizes the leading strand.

Question 8

It takes about the same amount of time for eukaryotic chromosomes to be replicated in vivo as it does for E. coli. Why is this true?

Accepted Answer

Eukaryotic chromosomes have multiple origins of replication, allowing for multiple replication forks to be initiated simultaneously, which compensates for the larger size of eukaryotic chromosomes. In contrast, E. coli has one unique origin of replication, which limits the rate of replication.

Question 9

The RNA primer at the beginning of each Okazaki fragment is removed by

Accepted Answer

The RNA primer is removed by the 5ʹ → 3ʹ exonuclease and 5ʹ phosphorylase activity of DNA polymerase I.

Question 10

The 3ʹ → 5ʹ exonuclease activity of E. coli DNA polymerase III accounts for the of polymerization.

Accepted Answer

The 3' → 5' exonuclease activity of E.coli DNA polymerase III provides a proofreading function, which significantly reduces the error rate during DNA replication by excising incorrectly paired nucleotides.

Question 11

The incorporation of new nucleotides into a growing strand of DNA occurs during .

Accepted Answer

The elongation stage is where new nucleotides are added to a growing strand of DNA by the DNA polymerase enzyme. Nucleation does not involve the addition of new nucleotides, initiation refers to the start of DNA replication, and the assembly of the protein machine is not directly involved in nucleotide incorporation.

Question 12

How many replisomes are required for one complete round of DNA replication in E. coli?

Accepted Answer

Two replisomes are required for one complete round of DNA replication in E. coli, as replication occurs bidirectionally from the origin of replication, with one replisome moving in each direction along the circular chromosome.

Question 13

During the elongation stage

Accepted Answer

During the elongation stage of DNA replication, DNA is replicated semiconservatively, meaning that each parental strand serves as a template for a new complementary strand to be synthesized. Replication proteins continue to unwind and open up the double helix, while DNA polymerase adds nucleotides to the growing strands. The protein machine does not disassemble during this stage, as it is necessary for the continued replication of DNA. Replication ends only after the completion of the elongation stage.

Question 14

DNA polymerase III requires a/an for synthesis of DNA to occur.

Accepted Answer

DNA polymerase III requires a DNA template, an RNA primer, and a free 3ʹ-OH end of a DNA strand to synthesize DNA.

Question 15

The e subunit of DNA polymerase III is responsible for its activity.

Accepted Answer

The e subunit of DNA polymerase III has 3ʹ → 5ʹ exonuclease activity, which is responsible for proofreading during DNA replication.

Question 16

DNA that has been liberally labeled with radioactive ¹⁴C is used as the template for replication. Replication is carried out in a medium containing only unlabeled nucleotides. After two rounds of replication, what percent of DNA molecules are still labeled?

Accepted Answer

The answer of DNA that has been liberally labeled with...

Question 17

The replication of DNA is because .

Accepted Answer

DNA replication is semiconservative, meaning that each daughter DNA molecule consists of one original (parental) strand and one new strand. This was first demonstrated by the Meselson-Stahl experiment in 1958.

Question 18

Meselson and Stahlʹs experiments involved growing E. coli on a medium containing ¹⁵N heavy nitrogen) which increased the density of the bacterial DNA. Cells were then grown on a medium containing only ¹⁴N. DNA samples were obtained for analysis after one, two and three rounds of replication generations) and centrifuged on a density gradient. The double-helical DNA forms bands in the gradient depending on its density. How many bands did Meselson and Stahl see after two generation of cells were grown on the ¹⁴N medium?

Accepted Answer

After two generations, there are two bands: one hybrid band containing both 15N and 14N, and one band containing only 14N DNA, consistent with the semi-conservative model of DNA replication.

Question 19

The processivity of E. coli DNA polymerase III holoenzyme accounts for all of the following except

Accepted Answer

The processivity of DNA polymerase III holoenzyme accounts for the relatively small number of enzymes needed to replicate the entire chromosome, the rapid rate of polymerization, and the ability of a single holoenzyme to add many nucleotides to a growing DNA chain. However, the directionality of polymerization is not a result of processivity, but rather the result of the chemistry of polymerization itself.

Question 20

At the normal rate of replication, about how many minutes does it take for the entire E. coli chromosome 4.6 × 10³kbp) to be duplicated?

Accepted Answer

E. coli replicates its chromosome in approximately 40 minutes under optimal conditions.

Quiz 20: Dna Replication, Repair, and Recombination

Enzymes that remain bound to their nascent chains through many polymerization steps are said to be .

E. coli DNA polymerase catalyzes polymerization in the directions) .

Which DNA polymerase is most responsible for chain elongation in E. coli?

The protein machine that carries out DNA replication is called .

Nick translation is a process for

Approximately base pairs are added per second during DNA in vivo replication in E. coli.

Polymerization of the lagging strand is catalyzed by .

It takes about the same amount of time for eukaryotic chromosomes to be replicated in vivo as it does for E. coli. Why is this true?

The RNA primer at the beginning of each Okazaki fragment is removed by

The 3ʹ → 5ʹ exonuclease activity of E. coli DNA polymerase III accounts for the of polymerization.

The incorporation of new nucleotides into a growing strand of DNA occurs during .

How many replisomes are required for one complete round of DNA replication in E. coli?

During the elongation stage

DNA polymerase III requires a/an for synthesis of DNA to occur.

The e subunit of DNA polymerase III is responsible for its activity.

DNA that has been liberally labeled with radioactive ¹⁴C is used as the template for replication. Replication is carried out in a medium containing only unlabeled nucleotides. After two rounds of replication, what percent of DNA molecules are still labeled?

The replication of DNA is because .

The processivity of E. coli DNA polymerase III holoenzyme accounts for all of the following except

At the normal rate of replication, about how many minutes does it take for the entire E. coli chromosome 4.6 × 10³kbp) to be duplicated?

Quiz 20: Dna Replication, Repair, and Recombination

Enzymes that remain bound to their nascent chains through many polymerization steps are said to be .

E. coli DNA polymerase catalyzes polymerization in the directions) .

Which DNA polymerase is most responsible for chain elongation in E. coli?

The protein machine that carries out DNA replication is called .

Nick translation is a process for

Approximately base pairs are added per second during DNA in vivo replication in E. coli.

Polymerization of the lagging strand is catalyzed by .

It takes about the same amount of time for eukaryotic chromosomes to be replicated in vivo as it does for E. coli. Why is this true?

The RNA primer at the beginning of each Okazaki fragment is removed by

The 3ʹ → 5ʹ exonuclease activity of E. coli DNA polymerase III accounts for the of polymerization.

The incorporation of new nucleotides into a growing strand of DNA occurs during .

How many replisomes are required for one complete round of DNA replication in E. coli?

During the elongation stage

DNA polymerase III requires a/an for synthesis of DNA to occur.

The e subunit of DNA polymerase III is responsible for its activity.

DNA that has been liberally labeled with radioactive 14C is used as the template for replication. Replication is carried out in a medium containing only unlabeled nucleotides. After two rounds of replication, what percent of DNA molecules are still labeled?

The replication of DNA is because .

The processivity of E. coli DNA polymerase III holoenzyme accounts for all of the following except

At the normal rate of replication, about how many minutes does it take for the entire E. coli chromosome 4.6 × 103 kbp) to be duplicated?

DNA that has been liberally labeled with radioactive ¹⁴C is used as the template for replication. Replication is carried out in a medium containing only unlabeled nucleotides. After two rounds of replication, what percent of DNA molecules are still labeled?

At the normal rate of replication, about how many minutes does it take for the entire E. coli chromosome 4.6 × 10³kbp) to be duplicated?