Chromosomes, Genes and DNA

Chromosomes, Genes and DNA

1. Key Facts

   • The genetic material- deoxyribonucelic acid- is contained in the Chromosomes
   • Chromosomes occur in functional pairs except in gametes
   • Genes are short sections of Chromosome that control specific characterisitics
   • Genes are therefore short lenghs of DNA

2. Structure of DNA

   • Backbone
     • Deoxyribose Sugar
     • Bases
     • Phosphate
     • Nucleotide
   • Bases
     • Pyrimidines
       • Thymine
       • Cytosine
     • Purines
       • Adenine
       • Guanine
     • Complementary base pairs
   • Double helix structure

3. Chromosomes

   • Humans have 46 Chromosomes
     • They are arranged into 23 pairs
   • A chromosome is a tightly coiled length of DNA
     • A GENE is a short length of DNA that codes for a protien or characteristic

4. Base triplets

   • Why have three?
     • "CCA" "CCC" "CCG" and "CCT" code for the same amino acid- this lowers the chance of mutatos
       • If the change in base results in a different amino acid being formed then it will form a different protein and may not function
         • Causes: Radiation e.g UV Light

5. Discovering DNA

   • Watson and Crick
     • Used modelling to hypothesise the 3 dimensional structure of DNA in the double helix format
   • Franklin and Wilkins
     • Studied the 3 dimensional structure of DNA using crystallograpgy (X-rays)
   • Chargaff
     • Discovered that there where equal amounts of guanine and cytosine as well as adenine and thymine

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