Unit 6 2/3/2025

Question 1

What were the 3 alternative models for DNA replication?

Answer 1

Question 2

What’s the conservative model for DNA synthesis?

Answer 2

The parental strands directs synthesis of an entirely new double stranded molecule

Question 3

What’s the semi conservative model for DNA synthesis?

Answer 3

The two parental strands of DNA each make a copy of itself- after one round of replication, the two daughter molecules each have one parental and new strand

Question 4

What’s the dispersive model for DNA replication?

Answer 4

The material in the two parental strands is dispersed randomly between the two daughter molecules. After one round of replication the daughter molecules contain a random mix of parental and new DNA

Question 5

What was the experiment using bacteria that meselson and Stahl performed to determine how DNA replicated?

Answer 5

Question 6

Which model did meselson and Stahl confirm was the way DNA was replicated due to their experiment?

Answer 6

Semi conservative

Question 7

How did the results of meselson and stahls experiment show the model for DNA experimenting is what it was?

Answer 7

They knew it wasn’t conservative since there was only 1 band of DNA not 2. They knew it wasn’t dispersive because if it was there model of the DNA would be more mixed.

Question 8

What’s are the steps of DNA replication

Answer 8

1. Various proteins attach to the origin of replication and open the DNA to form a replication fork
2. Helicase will unwind the DNA strands at each replication fork the proteins called SSBP’s bind to the DNA to keep it open. Topisomerase will help strain ahead of the replication fork by relaxing supercooling
3. The enzyme primase initiates replication by adding short segments of RNA (called primers) to the parental strand of DNA. (This is because DNAP III and DNAP I can only do their job without an existing strand to start it off)
   4.(antiparallel elongation) DNAP III attaches to each primer on the parental strand and moves in the 3’->5’ direction. As it moves it adds nucleotides to the new strands in the 5’->3’ direction.(this DNAP III follows helicase and is known as the leading strand and only requires one primer. The DNAP III on the other parental strand is known as the lagging strands and requires many primers)
4. The leading strand is synthesized in one continuous segment but since the lagging strand moves away from the replication fork it is synthesized in chunks and leaves behind Okazaki fragments
5. After DNAP III forms an Okazaki fragment, DNAP I replaces RNA nucleotides with DNA nucleotides. Then DNA ligase joins the Okazaki fragment forming a continuous DNA strand