chapter 11 DNA replication

Question 1

What is DNA replication?

Answer 1

DNA replication is the process by which genetic material is copied.

Question 2

What is used as templates during DNA replication?

Answer 2

The original DNA strands.

Question 3

Why is DNA replication important?

Answer 3

It ensures genetic information is accurately copied and passed to the next generation of cells.

Question 4

Which rule governs the complementarity of DNA strands?

Answer 4

The AT/GC rule, also known as Chargaff’s rule.

Question 5

What are the new strands formed during replication called?

Answer 5

Daughter strands.

Question 6

Name the three models of DNA replication proposed in the 1950s.

Answer 6

Conservative, semiconservative, and dispersive models.

Question 7

Which model was proven correct by the Meselson-Stahl experiment?

Answer 7

The semiconservative model.

Question 8

What isotopes were used in the Meselson-Stahl experiment?

Answer 8

Heavy isotope
15
𝑁
15
N and light isotope
14
𝑁
14
N.

Question 9

What is the origin of replication in E. coli called?

Answer 9

oriC (origin of Chromosomal replication).

Question 10

How does DNA synthesis proceed in bacteria?

Answer 10

Bidirectionally around the chromosome.

Question 11

What protein binds to the DnaA box sequences to initiate replication?

Answer 11

DnaA protein.

Question 12

Which proteins assist DnaA during the initiation of replication?

Answer 12

HU and IHF proteins.

Question 13

What is the role of GATC methylation in replication?

Answer 13

It regulates the initiation of DNA replication by marking sites for full or half-methylation.

Question 14

What is the function of DNA helicase?

Answer 14

It separates the two DNA strands by breaking hydrogen bonds.

Question 15

What does DNA gyrase do during replication?

Answer 15

Alleviates positive supercoiling ahead of the replication fork.

Question 16

What are single-strand binding proteins responsible for?

Answer 16

Keeping the separated DNA strands apart.

Question 17

What is the primary role of DNA polymerases?

Answer 17

To catalyze the attachment of nucleotides for new DNA synthesis.

Question 18

Which DNA polymerases are involved in normal replication in E. coli?

Answer 18

DNA pol I and III.

Question 19

What is the function of DNA pol I?

Answer 19

Removes RNA primers and replaces them with DNA

Question 20

What is unique about DNA pol III?

Answer 20

It is the main enzyme for synthesizing new DNA strands.

Question 21

How is the leading strand synthesized?

Answer 21

Continuously in the 5’ to 3’ direction.

Question 22

Why does the lagging strand require multiple primers?

Answer 22

Because it is synthesized discontinuously in small fragments called Okazaki fragments.

Question 23

What are Okazaki fragments?

Answer 23

Short DNA fragments synthesized on the lagging strand.

Question 24

What is meant by semi-conservative replication?

Answer 24

Semi-conservative replication means that each new DNA molecule consists of one parental strand and one newly synthesized daughter strand, preserving half of the original molecule.

Question 25

What are the important sequences in the bacterial origin of replication and what functions do they have in initiation of replication?

Answer 25

Important sequences in the bacterial origin of replication (oriC) include the AT-rich region, DnaA boxes, and GATC methylation sites. The AT-rich region unwinds easily, DnaA boxes bind the DnaA protein to initiate replication, and GATC methylation sites regulate replication timing.

Question 26

Identify the proteins involved in DNA replication in a figure and state the functions of each: DNA polymerase III DNA polymerase I: Helicase: Topoisomerase: Single-strand binding proteins (SSBs): DNA ligase: DNA primase:

Answer 26

DNA polymerase III: Synthesizes the leading and lagging strands by adding nucleotides in the 5’ to 3’ direction. DNA polymerase I: Removes RNA primers and replaces them with DNA. Helicase: Unwinds the DNA helix by breaking hydrogen bonds between strands. Topoisomerase: Relieves supercoiling stress ahead of the replication fork. Single-strand binding proteins (SSBs): Prevent reannealing of separated DNA strands. DNA ligase: Seals nicks between Okazaki fragments on the lagging strand. DNA primase: Synthesizes short RNA primers needed to start DNA synthesis.

Question 27

Describe the difference between leading and lagging strand synthesis and be able to describe which strand is which in a diagram.

Answer 27

The leading strand is synthesized continuously in the 5’ to 3’ direction toward the replication fork. The lagging strand is synthesized discontinuously in fragments (Okazaki fragments) in the 5’ to 3’ direction away from the replication fork.

Question 28

In what ways is DNA replication different between prokaryotes and eukaryotes?

Answer 28

Prokaryotic DNA replication occurs in a circular chromosome with a single origin of replication, while eukaryotic replication involves linear chromosomes with multiple origins. Eukaryotic replication is also more complex due to chromatin structure and cell cycle regulation.

Question 29

What challenge do telomeres pose in DNA replication?

Answer 29

Telomeres prevent complete replication of the chromosome ends, leading to progressive shortening with each cell division. This challenge is addressed by the enzyme telomerase, which extends the telomeres to protect genetic information.