Introduction to genetics

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  • Introduction to Genetics
    • DNA as the Genetic Material
      • 1900 Chromosomes = likely carriers of genes
      • Chromosomes = DNA and protein - protein varied from cell to cell
        • Therefore protein = genetic material - DNA lacked diversity
      • Each daughter cell = same chromosome number in each species
      • Experimental proof:
        • Hershey and Chase
          • Bacteriophage and E. coli
        • McLeod, McCarthy, Avery
          • S and R strains of S.  pneumoniae and mice
    • DNA Structure: The Double Helix
      • 1953
        • Watson, Crick and Franklin
          • 3D structure of DNA
      • Double stranded, antiparallel helix of complementary bases
        • Head = 3' Tail = 5'
        • B form = right handed twist
        • Purines
          • Adenine and Guanine
        • Pyrimidines
          • Thymine and Cytosine
    • Genes and Proteins
      • Genes are in the DNA, they are made up of DNA nucleotide sequences
      • There are different types of proteins
        • Structural
        • Pores in membranes
        • Receptor proteins
        • Enzymes
      • Mutant genes give rise to defective proteins
        • A mutant enzyme can be harmful or have a neutral effect
          • Phenylketonuria
          • Alkaptonuria
      • Inborn errors of metabolism (Garrod)
        • From these, hereditary diseases arise due to a defect in enzymes
    • Gene Expression: The Central Dogma
      • The genetic code for protein is found in one strand only
      • Proteins consist of one or more polypeptide chains
      • 1.5% of the gene is contributed to coding for protein
        • Unsure on what the rest is for - most likely regulatory, controlling the activity of the gene
      • DNA codes for protein indirectly DNA --> RNA --> Protein
        • This is known as the central dogma for genetics
      • There are 20 different amino acids
        • There are 4 base combinations
          • There are 64 possible 3-base sequences
            • Therefore the genetic code is degenerative
              • Three codons do not code for amino acids - they code for 'STOP'
                • UAA, UAG. UGA recognised by protein factors - NOT tRNA
      • RNA contains ribose sugar instead of deoxyribose (as in DNA)
        • There are 3 types of RNA
          • transfer RNA
          • messenger RNA
          • ribosomal RNA

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