1. DNA Replication Chapter 12-2

2. What is the Human Genome Project? Every chromosome contains a specific group of genes Between our 46 chromosomes, our cells contain at least 35,000 genes Knowing the location and function of all the genes may help us fight against illness What role do stem cells play in gene therapy? –By removing damaged tissue, altering it in a lab and replacing it into a body, proper function may resume!

3. What is a Gene? More than a piece of DNA, a gene is a specific sequence of nucleotides Each nucleotide consists of –5 carbon sugar –Phosphate group –1 of 4 different nitrogen bases The four nitrogen bases: –(A) Adenine, (T) Thymine, (C) Cytosine, (G) Guanine for DNA –(A) Adenine, (U) Uracil, (C) Cytosine, (G) Guanine for RNA

4. Base Pairing Rule: Adenine will always pair with Thymine in DNA: –A-T or T-A Cytosine will always pair with Guanine in DNA: –C-G or G-C IN RNA: T is replaced with U –A-U or U-A

5. DNA is a Double Helix Imagine DNA to look like a ladder –Each side of the ladder is said to be “Complimentary” to the other –The 5 CARBON SUGAR and PHOSPHATE make up the sides of the ladder –The NITROGEN BASES make up the steps

6. DNA Replication: 3 easy steps 1.DNA is UNZIPPED by one Enzyme into two separate strands 2.Another Enzyme moves alone each strand and attaches nucleotides to the exposed bases 3.Voila! Two new Double Stranded molecules of DNA

7. Step 1: Unzipping The DNA is unzipped in the middle by an enzyme This exposes nitrogen bases –Each base pair is ripped apart exposing both bases

8. Step 2: Adding Bases Once the DNA is unzipped, a SECOND enzyme (DNA polymerase) moves along each strand in opposite directions As DNA polymerase moves along, it grabs FREE FLOATING nucleotides and attaches them to the EXPOSED nitrogen bases This is where the base pairing rule comes in handy

9. Step 3: VOILA! Bases continue to be added until the two original strands completely separate This creates two new DOUBLE STRANDED molecules of DNA

10. Side Notes: DNA replication happens during INTERPHASE (more specifically, S Phase) DNA must be in its long and stringy CHROMATIN form to be replicated Replication occurs at hundreds of locations along a single chromosome