Unit 6: Topic 2 - Replication Flashcards
In what direction is DNA synthesized?
DNA is synthesized in the 5’ to 3’ direction.
What is the name of the enzyme that is in charge of DNA synthesis?
DNA Polymerase 3 is the main enzyme involved; it catalyzes DNA synthesis.
DNA polymerase 1 and 2 are involved in the repairing and proofreading of DNA.
DNA replication is a…
a) conservative process
b) semiconservative process
c) dispersive process
b) semiconservative process
Explanation:
Semiconservative process: the two strands of DNA unwind from each other, and each acts as a template for the synthesis of a new, complementary strand. This results in two DNA molecules with one original strand and one new strand.
This differs from the…
Conservative process: DNA replication results in one molecule that consists of both original DNA strands (identical to the original DNA molecule) and another molecule that consists of two new strands (with exactly the same sequences as the original molecule)
Dispersive process: DNA replication results in two DNA molecules that are mixtures, or “hybrids,” of parental and daughter DNA. In this model, each individual strand is a patchwork of original and new DNA.
The conservative and dispersive methods of DNA replication were the hypotheses of DNA replication before scientists discovered that DNA replication was a semi-conservative process
Diagram
What is an origin of replication (ori), and what is a replication fork?
The origin of replication (ori) is a sequence of DNA at which replication is initiated on a chromosome, plasmid, or virus.
A replication fork is a region where a cell’s DNA double helix has been unwound and separated to create an area where DNA polymerases and the other enzymes involved can use each strand as a template to synthesize a new double helix.
Two replication forks going in opposite directions form a replication bubble.
What is the role of helicase in DNA replication, and how does it do its job?
Helicase is an enzyme that unwinds the two DNA strands, creating a replication fork. Helicase uses free energy from ATP hydrolysis to change shape and wedge into the DNA, locally breaking hydrogen bonds between bases on the two strands and separating them.
Helicase = scissors
What is the role of topoisomerase in DNA replication?
Topoisomerase is an enzyme that prevents the DNA double helix ahead of the replication fork from getting too tightly wound as the DNA is opened up - it relaxes the supercoiling in front of the replication fork.
What is the role of primase in DNA replication?
Primase is an enzyme that places down RNA primers (short RNA sequences complementary to the template strand of DNA) to create a starting place for DNA polymerase to bind. They are the initiators.
Note: In most organisms, primers are a short single strand of RNA, but in some viruses it is DNA.
What is the difference between the leading strand and the lagging strand during DNA replication?
DNA polymerase synthesizes new strands of DNA continuously on the leading strand and discontinuously on the lagging strand.
The leading strand is oriented so that it can grow continuously at its 3ʹ end as the fork opens up. The other new strand—the lagging strand—must be synthesized differently because it grows in the direction away from the replication fork.
Remember: DNA is read in a 3’ to 5’ direction and is synthesized in a 5’ to 3’ direction (which is what happens on the leading strand). On the lagging strand, however, DNA is read in a 5’ to 3’ direction. which is why the new strand is synthesized discontinuously.
What are Okazaki fragments?
Okazaki fragments are the small fragments that are formed as a result of the discontinuous DNA synthesis on the lagging strand.
What is the role of ligase in DNA synthesis?
Ligase is an enzyme that links the Okazaki fragments together and makes the lagging strand whole.
Ligase = glue
