Why must DNA

be replicated?

Because each cell in the human body comes from a single fertilized egg.

What is semiconservative

replication?

When two resulting DNA

copies each have 1 strand of

parental DNA and 1 strand

of newly constructed DNA.

What experiment proved 

semiconservative replication ?

Give details.

The Meselson - Sahl experiment.

Bacteria were grown in heavy N15 and then after some time transferred to a lighter N14. They were then mixed with Ceasium Chloride. If the bacteria contained N15 DNA they would have sunk to the bottom of the test tube, if they contained N14 DNA they would have floated to the top. In the end some DNA floated in the middle, proving that 1 strand of DNA was from N15 and one was from N14.

What is the complete

process of semiconservative

replication known as?

Semidiscontinuous

Replication

-A- replication

1)  -B- unwinds DNA, creating -C-.

2)  -D- bind to the single strands to keep them apart.

3)  -E- creates -F- on the single strands as a starting off point for -G-.

4)  -H- is attatched at these points on each strand and is held on by a -I- which also moves it along.

5)  -J- = towards fork (-K-)      -L- = away from fork (-M-)           <- (direction)

6)  The -N- strand forms short -O-, ie discontinuous replication.

7)  -P- then removes the -Q- and fills the gap with -R-.

8)  -S- are then joined by -T-.

 A = Semidiscontinuous                                       B = Helicase                                                C = Replication fork

D = Single stranded binding protein                 E = Primase                                                F = RNA Primers

G = DNA Polymerase III                                      H = DNA Polymerase III                         I = Sliding Clamp

J = Leadin strand                                                  K = 5-3                                                         L = Lagging strand

M = 3-5                                                                    N = Lagging                                             O = Okazaki Fragments

P = DNA Polymerase I                                         Q = RNA Primers                                        R = DNA

S = Okazaki Fragments                                        T = Ligase.