12.2 Replication of DNA

Semiconservative Replication Semiconservative Replication- When

the parental strands of DNA separate (serving as templates) and produce DNA molecules that have 1 strand of parental DNA and 1 strand of new DNA

DNA replication occurs during Interphase of Mitosis and Meiosis.

Why it is important Makes duplicate copies of DNA to pass along all

genetic info Without replication, species could not survive During replication, each strand serves as a pattern

to make a new DNA molecule

3 Stages of Semiconservative replication: Unwinding, Base Pairing, and Joining.Step 1: UnwindingAn enzyme (DNA helicase) unwinds and

unzips the double helix. Hydrogen bonds are broken, leaving a leading strand and a lagging strand.

Single-stranded binding proteins keep the strands separated during replication.

RNA primase adds a short segment of RNA (RNA primer) on each strand

Leading strand- moves in the same direction as the replication fork. It replicates continuously. Lagging strand- moves in the opposite direction. It does NOT replicate continuously.

Step 2: Base PairingAn enzyme (DNA polymerase) aids in adding new DNA

nucleotides to the chainSince A binds to T and C binds to G, an identical copy is

made.Okazaki fragments- Short segments of DNA which will later

be connected by DNA ligase. (Lagging strand only)

Step 3: JoiningDNA polymerase comes to a RNA primer

on the DNA, removes the primer, and fills in the place with DNA nucleotides. Once replaced, DNA ligase links (or zips up) the 2 sections.

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA%20Replication%20Fork

DNA replication animation

The importance of nucleotide sequence

The sequence of nucleotides form the unique genetic information of an organism.

The more closely related two organisms are, the more alike the sequence of nucleotides in the DNA will be.

Ex: Gel Electrophoresis

Gel Electrophoresis