1. Chp. 12: DNA

2. DNA - History James Watson- American biochemist
Francis Crick- English physicist
Rosalind Franklin- English crystallographer

3. The Discovery
Watson & Crick discovered that DNA was a double helix with chains running in opposite directions (1953).
Franklin produced a photo by passing x-rays through DNA (showed it was a double helix)

4. Double Helix

5. DNA- Deoxyribonucleic Acid
Made of Deoxyribose (sugar), phosphate groups, and a nitrogen base

6. DNA looks like a twisted staircase/ladder, double helix
Nucleotides nucleic acid DNA
(smallest) (largest)
DNA looks like a twisted staircase/ladder, double helix
RNA- Ribonucleic Acid

7. There are 4 possible nitrogen bases
Adenine (A)
Guanine (G)
Cytosine ( C)
Thymine (T)
Discovered by Chargaff
Nucleotides combine through condensation reactions.

8. The nitrogen bases are pairs that make up the rungs (steps) of the ladder.
Adenine pairs w/Thymine (A-T)
Cytosine pairs w/Guanine (C-G)
These pairs are held together by a weak hydrogen bond.

9. The sides of the ladder are formed by the deoxyribose & phosphate groups.
They are held together by covalent bonds

10. Importance of DNA Genetic material of living things is made of DNA
Organisms are different because the order of nucleotides are different
Use genetic information to determine evolutionary relationships. The more closely related they are, the more alike their nucleotide sequence.
All Humans are 99.9 % identical. Humans and chimps DNA are 98.8% identical.

11. Human Genome Project
Worked together to determine the nucleotide sequence for humans

12. DNA Replication DNA is copied during mitosis (Interphase)
During replication each strand serves as a model to make a complementary strand.
DNA Helicase (enzyme) breaks the hydrogen bonds that hold the nucleotides together, unzipping the DNA.

13. Replication cont…
As the DNA unzips, free nucleotides that are in the nucleus bond to the single strands by base pairing.
DNA Polymerase (enzyme) ensure the right bases go in the right spot
As a result, each new strand formed is a complement of one of the original strands.

14. Forms 2 DNA molecules that are identical to the parent