Chapter 16.2 - DNA Replication

Question 1

Important points about DNA replication (4)

Answer 1

1. DNA replication occurs in the same way in all organisms
2. DNA must be copied accurately
3. Genetic info (DNA) must be transmitted to daughter cells
4. DNA directs its own replication

Question 2

Actual Process of DNA Replication (5)

Answer 2

1. DNA strands separate
2. Enzymes bind and use each strand as a template to make a new strand
3. Semiconservative replication
4. Each new double helix consists of one old and one new strand
5. DIAGRAM

Question 3

Semiconservative model

Answer 3

The two strands of the parental molecule separate, and each functions as a template for synthesis for a new, complimentary strand

Question 4

Origin of Replication (4)

Answer 4

1. Replication of each DNA molecule begins at sites with a specific sequence of nucleotides
2. A-T rich sequence at origin of replication
3. Specific proteins attach and separate strands
4. Check diagrams!

Question 5

Replication Fork

Answer 5

At the end of each replication bubble. This is a Y shaped region where the parental strands of DNA are being unwound by several types of proteins.

Question 6

Origins of replication in a Eukaryote

Answer 6

DNA helix must unwind to expose template strand. See page 338!

Question 7

3 Proteins involved in unwinding DNA

Answer 7

1. Helicase
2. Single-stranded bonding protein
3. Topoisomerase

Question 8

Helicase

Answer 8

• unwinds strands

- breaks hydrogen bonds between nitrogenous bases

Question 9

Single-stranded binding protein

Answer 9

-binds to the unpaired DNA strands, keeping them from re-pairing after the parental strands separate

Question 10

Topoisomerase

Answer 10

-an enzyme that helps relieve the strain by breaking, swivelling and rejoining DNA strands

Question 11

Enzymes involved in DNA synthesis (2)

Answer 11

1. DNA Polymerase

2. Primase

Question 12

DNA polymerase

Answer 12

-catalyzes the synthesis of new DNA by adding nucleotides to the 3’ end of a preexisting chain

Question 13

Primase

Answer 13

-makes the RNA primer and provides initial 3’ OH

Question 14

Directional Polymerization of Nucleotides (4)

Answer 14

1. DNA polymerase catalyzes addition of nucleotide triphosphate to 3’ end of growing strand
2. Synthesis of Nucleic Acid is always 5’3’ and antiparallel to template
3. Nucleotide added is determined by base on template strand
4. Replication proceeds in both directions and occurs simultaneously in both strands

Question 15

Lagging Strand

Answer 15

Discontinues synthesis

Question 16

Leading strand

Answer 16

Continuous synthesis

Question 17

Okazaki fragments

Answer 17

Fragments of the lagging strand (separately primed)

Question 18

Proofreading (4)

Answer 18

1. DNA polymerase can detect and remove non-complementary nucleotides during replication
2. If incorrectly paired nucleotides are missed, other enzymes will later remove and replace the mismatched nucleotide
3. These DNA repair systems also repair damaged DNA
4. Result in mutation if not corrected. Mutations are perpetual

Question 19

DNA ligase

Answer 19

An enzyme that joins all the sugar-phosphate backbones of the Okazaki fragments into a continuous strand

Question 20

A summary of bacterial DNA Replication

Answer 20

Diagram on 341

Question 21

Mismatch Repair

Answer 21

Other enzymes remove and replace incorrectly paired nucleotides that have resulted from replication errors

Question 22

Termination of Replication in prokaryotes

Answer 22

• chromosomes are circular

- replication proceeds in both directions to end around 180 degrees

Question 23

Termination of Replication in eukaryotes

Answer 23

• chromosomes are linear
• replication terminates at nucleotide sequences known as telomeres
• no genes present

Question 24

Telomeres (3)

Answer 24

Telomeres do not contain genes and instead consists typically of repetitions of one short nucleotide sequence

Question 25

Telomerase

Answer 25

An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells, thus resorting to their original length and compensating for the shortening.

*produced in 90% of cancer cells