DNA NOTES DNA STRUCTURE DNA is constructed of

DNA NOTES

DNA STRUCTURE • DNA is constructed of three parts • A sugar molecule called deoxyribose • A phosphate group • Nitrogen containing base • 4 nitrogen containing bases are • • Adenine – A Guanine – G Cytosine – C Thymine - T

DNA STRUCTURE • The four nitrogen containing bases are divided up into 2 groups • Purines: Adenine and Guanine • Pyrimidines: Thymine and Cytosine

Nucleotides

The Double Helix • In 1953, Watson and Crick created a model for the DNA molecule. The proposed model was 2 nucleotide chains that are wrapped like a spiral staircase. • This spiral staircase eventually became known as the double helix.

The Double Helix • Rosalind Franklin was the person who used xrays to look at DNA. • Watson and Crick then used her x-rays to see the spiral shape of the DNA.

The Double Helix • The reason that the DNA molecule is twisted is because the molecules consist of complimentary pairs. • These pairs are pairs of nucleotide bases • Thymine always pairs with adenine • Cytosine always pairs with guanine • However in RNA there is no thymine instead adenine will pair with uracil. • The staircase is caused by the random order of the pairing and length of each molecule.

RNA • The sugar molecule of RNA is ribose. • In RNA thymine is replaced by uracil, but still pairs with adenine. • There are three types of RNA – Messenger RNA (m. RNA) – Transfer RNA (t. RNA) – Ribosomal RNA (r. RNA)

Genetic Code • The correlation between a nucleotide sequence and amino acid sequence is called the genetic code. • The genetic information necessary for making proteins is encoded in a series of 3 m. RNA nucleotides. Each combination of 3 nucleotides is called a codon. • There a total of 64 codon sequences.

WHAT IS A CODON? Three nucleotides (on m. RNA) make up a codon. A codon then codes for a specific protein.

Codon Table

What is the difference between DNA- molecule composed of two chains of nucleotides in a right handed double helix structure Genes- A sequence of a DNA nucleotide that occupies a specific site on a chromosome. This site serves as a template for synthesis of a specific protein Chromosome - made up of DNA and holds many genes (23 pairs, 46 total) Allele- one of two forms of a gene (one from father one from mother).