6.3 DNA Replication

Question 1

Replication complex (replisome)

Answer 1

• a set of specialized proteins that assist the DNA polymerases

Question 2

Helicase

Answer 2

the enzyme responsible for unwinding the DNA, generating two single-stranded template strands ahead of the polymerase

Question 3

DNA topoisomerases

Answer 3

• introduce negative supercoils.
  They do so by working ahead of helicase, nicking one or both strands, allowing relaxation of the torsional pressure, and then resealing the cut strands
• alleviate this torsional stress and reduce the risk of strand breakage

Question 4

Semiconservative

Answer 4

• one parental strand is retained in each of the two resulting identical double stranded DNA molecules

Question 5

How does DNA polyermase read the template strand?

Answer 5

• read the template strand in a 3′ to 5′ direction while synthesizing the complementary strand in the 5′ to 3′ direction.

Question 6

Which processes occur 5’ to 3’?

Answer 6

• DNA synthesis
• DNA repair
• RNA transcription
• RNA translation (reading of codons)

Question 7

Leading strand

Answer 7

• stand copied in continuous fashion

Question 8

Lagging Strand

Answer 8

• strand that is copied in a direction opposite the
  direction of the replication fork.

Question 9

Primase

Answer 9

• synthesizes a short primer (roughly 10 nucleotides) in the 5′ to 3′ direction to start replication on each strand
• These short RNA sequences are constantly being added to the lagging strand because each Okazaki fragment
  must start with a new primer

Question 10

DNA polymerase III

Answer 10

-Synthesizes daughter strands for prokaryotes

Question 11

DNA polymerases α, δ, and ε

Answer 11

-Synthesizes daughter strands for eukaryotes
- incoming nucleotides are 5′ deoxyribonucleotide
triphosphates: dATP, dCTP, dGTP, and dTTP

Question 12

DNA polymerase I

Answer 12

• prokaryotes
• removes RNA
• adds DNA nucleotides where the RNA primer had been.

Question 13

RNase H

Answer 13

• eukaryotes
  -removes RNA
• adds DNA nucleotides where the RNA primer had been.

Question 14

DNA polymerase δ (Delta)

Answer 14

• fills in the gaps left behind when RNA primers are removed

Question 15

DNA polymerase γ (Gamma)

Answer 15

replicates mitochondrial DNA

Question 16

What do DNA polymerases β (Beta) and ε (epsilon) do?

Answer 16

• important to the process of DNA repair

Question 17

What do DNA polymerases δ (Delta) and ε (Epsilon) do when together?

Answer 17

• assisted by the PCNA protein, which assembles into a trimer to form the sliding clamp. The clamp helps to strengthen the interaction between these DNA polymerases and the template strand

Question 18

Limits of DNA polymerase?

Answer 18

• does an excellent job of synthesizing DNA, it unfortunately cannot complete synthesis of the 5′ end of the strand
• Thus, each time DNA synthesis is carried out, the chromosome becomes a little
  shorter.