DNA Replication

Question 1

What does it mean when we say DNA replication is semiconservative?

Answer 1

Semiconservative replication means when the two strands of DNA separate, each strand serves as a template for the synthesis of a new strand. Each original nucleotide strand remains intact (conserved) despite no longer being combined in the same molecule. Therefore, the original DNA molecule is half (semi) conserved

Question 2

What did Meselson and Stahl’s experiment consist of?

Answer 2

They were searching which model of replication applied to DNA. The cultured E. coli in N 15 isotope and then in N 14 for many generations. They used centrifugation to separate the resulting DNA. Their experiment revealed that DNA replication is semiconservative.

Question 3

What is a replicon?

Answer 3

A unit of replication consisting of DNA from the origin of replication to the point at which replication on either side of the origin ends.

Question 4

What is the replication fork?

Answer 4

The point at which double stranded DNA molecules separate into two single strands that serve as templates for replication

Question 5

Compare eukaryotic DNA replication to bacterial

Answer 5

Eukaryotes have linear chromosomes with multiple origins of replication compared to bacterial circular chromosomes with one origin.

Question 6

What three things does DNA replication require?

Answer 6

1. A template of single stranded DNA
2. Raw materials (dNTPs)
3. Enzymes and other proteins to read the template and assemble a new DNA molecule

Question 7

In what direction does replication occur?

Answer 7

always from 5’ to 3’

Question 8

What are the four general steps of bacterial replication?

Answer 8

1. initiation
2. unwinding
3. elongation
4. termination

Question 9

What is continuous replication?

Answer 9

Replication of the leading strand of DNA in the same direction as that of unwinding, allowing new nucleotides to be added continuously to the 3’ end of the new strand

Question 10

What is discontinuous replication?

Answer 10

Replication of the lagging strand of DNA in the direction opposite that of unwinding, which means that DNA must be synthesized in short stretches (Okazaki fragments); essentially, this replication runs out of template and must start again

Question 11

What are Okazaki fragments?

Answer 11

Short lengths of newly synthesized DNA produced by discontinuous replication on the lagging strand

Question 12

What order does replication happen in/what enzymes work when?

Answer 12

1. ORC
2. Helicase
3. Single-stranded binding proteins (SSBs)
4. Primase
5. DNA Polymerase
6. Ligase

Question 13

What does helicase do? When does it function?

Answer 13

Unwinds double stranded DNA by breaking the H-bonds between the bases of the two strands.

Helicase is present with ORC in G1, but only functions in S phase.

Question 14

What is DNA Gyrase?

Answer 14

A topoisomerase that relieves torsional strain that builds up ahead of the replication fork as it is unwound

Question 15

What is primase?

Answer 15

An enzyme that lies down RNA primers to provide a 3’ OH group for DNA synthesis to begin; DNA Polymerase cannot function without an available 3’ end

Question 16

What is the function of DNA Polymerase III

Answer 16

synthesizes new DNA nt strands by adding them to the 3’ end during elongation

Question 17

What is the function of DNA Polymerase I?

Answer 17

Removed RNA primers and replaces them with DNA nucleotides

Question 18

What type of exonuclease activity does DNA Pol III have?

Answer 18

only 3’-5’

Question 19

What type of exonuclease activity does DNA Pol I have?

Answer 19

both 5’-3’ and 3’-5’

Question 20

What does ligase do?

Answer 20

catalyzes the formation of a phosphodiester bond between adjacent 3’ OH groups and 5’ phosphate groups in DNA molecules without adding more nucleotides; seals the nicks

Question 21

What is ORC?

Answer 21

The origin recognition complex, a multiprotein complex that recruits helicase to unwind DNA. ORC only functions in G1.

Question 22

What are licensing factors?

Answer 22

proteins that must be present for origin identification before replication can be initiated

Question 23

What is the “end replication problem”

Answer 23

Telomeres in linear chromosomes of somatic cells get shorter after each replication

Question 24

What is telomerase?

Answer 24

An enzyme the replicates the ends of telomeres of eukaryotic chromosomes. The RNA portion of this enzyme has a template that is complementary to repeated sequences in the telomere and pairs with them, providing a template for the synthesis of additional copies of the repeats

Question 25

What is Werner Syndrome?

Answer 25

A form of premature aging in which the subject loses the WRN protein. As a result, the individual has an accelerated loss of their telomeres.