Genetics Lecture #3 (Prokaryotic)

What chemical reaction fuels the synthesis of new DNA?

The breaking of bonds between phosphate groups on an incoming dNTP

What is typically found on the 5 prime end of DNA? What about the 3 prime end?

5: sugar molecule

3: hydroxyl group

What is meant when DNA replication is considered "semi-conservative replication"?

Each strand in the parental helix serves as a template for the daughter strands

What causes DNA replication to begin?

an initiator proteins binds to the origin of replication, causing DNA to unwind for a short section

Where the DNA initially unwinds, is there a larger amount of G/C pairs or A/T combos? Why?

A/T, because they only have 2 hydrogen bond rather than 3

What enzyme is responsible for breaking hydrogen bonds between nucleotide pairs during replication?

Helicase

After helicase separates DNA into 2 single strands, what prevents the matching strands from rebinding?

single-strand-binding proteins bind to the newly separated strands, blocking the matching nucleotides

What does DNA primase do?

synthesizes a short RNA primer in the 5-3 prime direction that attaches to the DNA strands

What does DNA Polymerase III do?

extends the RNA primers built by DNA primase by synthesizing DNA in a 5-3 prime direction on both template strands

What is the difference between the leading and lagging strands of DNA?

On the leading strand, DNA synthesis is continuous and moves in the direction of the replication fork.

On the lagging strand, DNA synthesis is discontinuous and grows in the opposite direction of the replication fork

What are the short fragments of DNA called on the lagging strand during replication?

Okazaki fragments

What does DNA Polymerase 1 do?

extends the 3 prime end of Okazaki fragments, and removing the RNA primer

What does DNA Ligase do?

combines 2 Okazaki fragments

What do Topoisomerases do?

remove excess supercoiling in DNA strands

What are the two types of Topoisomerase?

Type 1: breaks one strand of DNA to remove supercoiling

Type 2: breaks both strands of DNA to remove super coiling

What is the function of Beta-Clamps?

Binds with DNA Polymerase 3 to help it stay attached to DNA strands, increasing its productivity

What is referred to in the trombone model of DNA replication?

DNA Polymerase 3 come in pairs, which form a dimer. DNA Polymerase 3 must travel in a 5-3 prime. One strand of DNA forms a loop, so both DNA Pol 3 can travel in a 5-3 prime direction, while staying connected via the dimer.

What is the difference in the actions of DNA Pol 1 and DNA Pol 3?

DNA Pol 1:

- 5-3 DNA synthesis

- 5-3 exonuclease activity

- 3-5 exonuclease activity

DNA Pol 3:

- 5-3 DNA synthesis

- 3-5 exonuclease activity

True or False: topoisomerase and gyrase are the same thing

True

What type of primase is DNA Primase

RNA primase