DNADeoxyribonucleic Acid

Purpose• DNA codes for

proteins and is the blueprint for life.

• The same DNA is found in all cells in your body (sex cells have half of the DNA)!

• Only certain parts of the DNA molecule are read and used in each cell type.

DNA and Chromosomes

• Prokaryotes – DNA in circular form

called “plasmid” – E. Coli has over 4.6

million base pairs!

• Eukaryotes – Linear DNA in form of

chromosome– Human cells contain

about 3 billion base pairs!

Chromosome Composition

• A Nucleosome is DNA tightly wound around protein spheres called “histones”

• Nucleosomes supercoil and become thick fiber of chromosomes

• Nucleosomes play role in gene regulation – turning off and on genes

Structure

• Discovered by Watson and Crick in 1953

• Shaped like a twisted ladder called a “double helix”

Rosalind Franklin

• Used X-Ray diffraction to get information about the structure of DNA:

Chargaff’s rules

• The relative amounts of adenine and thymine are the same in DNA

• The relative amounts of cytosine and guanine are the same.

Nucleotide

• Subunit of DNA

• made up of a sugar, phosphate and one nitrogen base.

What makes up the sides of DNA Ladder?

1. Deoxyribose sugar

2. Phosphate group

• Run in opposite directions called “anti-parallel”

• Important when copying DNA

• Run in direction 5’-3’

Nitrogen bases make up RungsPurines Pyrimidines

(double ring) (single ring)

Adenine-------(double H bond)--------Thymine

Guanine-------(triple H bond)---------Cytosine

Putting it all together

• The order of bases in DNA makes you different from the person sitting next to you!