DNA StructureThe deoxyribonucleic acid, DNA, is a long chain of

nucleotides which consist of• Deoxyribose (a pentose = sugar with 5 carbons) • Phosphoric Acid • Organic (nitrogenous) bases (Purines - Adenine and

Guanine, or Pyrimidines -Cytosine and Thymine)

Purine (A+G)

Pyrimidine (T+C)

Bases

a nucleotide, a building block of DNA. It is a phosphate ester of a nucleoside Nucleotide Nucleoside

a nucleotide, a building block of DNA

Note numbering system for carbons in ring

Also note the difference between a ribose used for building DNA and one used for RNA

DNA and RNA chains are made by connecting nucleotides together via chemical bonds

What is this chain RNA or DNA?

• four different types of nucleotide possible in a DNA sequence, adenine, cytosine, guanine and thymine (ATCG)

• Nucleotides are situated in adjacent pairs in the double helix.

• Thymine and adenine can only make up a base pair

• Guanine and cytosine can only make up a base pair

• Double-stranded DNA is simply two chains of single- stranded DNA, positioned so their "bases" can interact with each other.

• The sugar-and-phosphate 'backbone' is red, and the bases are blue.

• the two strands travel in opposite directions; "anti-parallel".

• The bases in the middle "pair up" with bases on the opposite strand, A+T, G+C

• Hydrogen bonds hold stucture together

Genome- entire complement of genetic information.

• Includes coding and non coding

• Genes (exons and introns) – Alleles are different gene forms

• Useful DNA for doing genome analysis

from Molecular Biology of the Cell by Alberts et al.

Several layers of packaging contribute to the 10,000-fold compaction of the genome

DNA isolation and purification

• Important to obtain clean intact DNA in sufficient quantities to work with

• Always do on ice

Most purification procedures include many of the following steps

1. Lysis of cells to release contents including DNA2. Treatment with EDTA to bind divalent cations3. Proteinase K treatment to digest proteins and tissue away from

DNA4. Separation of DNA from other contaminants in cellular soup using

chemical and physical differences e.g. differential solubilities, precipitation, binding to columns and centrifugation