DNA STRUCTURE

Unit 4 – Part 1

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!

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)

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

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

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.