1. DNA Structure
Unit 4 – Part 1

2. DNA Facts DNA DeoxyriboNucleic Acid Basis for all living things
Foundation for all diversity & unity on Earth
Every living thing has DNA. That means that you have something in common with a zebra, a tree, a mushroom and a beetle!!!!
DNA is too small to see, but under an electron microscope it looks like a twisted up ladder!

3. History of DNA Frederick Griffith
Discovers that a factor in diseased bacteria can transform harmless bacteria into deadly bacteria. (1928)
Rosalind Franklin
X-ray photo of DNA. (1952)
Watson and Crick
described the DNA molecule from Franklin’s X-ray.(1953)

4. Structure of DNA Nucleotide Small units that link together to form DNA
Made of 3 parts
Phosphate Group
5-C sugar molecule
deoxyribose
Nitrogen Base

5. Structure of DNA cont’d.
Nitrogen (N) base
N base makes nucleotides different
4 bases
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
2 main groups of bases
Purines
Double ring of C & N atoms
Includes adenine and guanine
Pyrimidines
Single ring of C & N atoms
Includes thymine and cytosine
Base pairing rules
Purines bind to pyrimidines
Adenine binds to thymine
Guanine binds to cytosine

6. Structure of DNA cont’d.
Double Helix
Model created by James Watson & Francis Crick
Structure of DNA
“spiral staircase” made of 2 strands of nucleotides twisting around a central axis.
Also known as a “twisted ladder”
Sides of ladder are made of alternating sugar and phosphate units held together with strong covalent bonds.
Rungs are made up of a purine and a pyrimidine held together by weak Hydrogen (H) bonds.
Base pairing is specific and follows Chargoff’s rule,
A ~ T and G ~ C a.k.a. the Complementary base pairing rule.