DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
DNA (DNA = deoxyribonucleic acid)
• DNA is the genetic material of all living cells and of many viruses.
• DNA is: an alpha double helix of two polynucleotide strands.
• The genetic code is the sequence of bases on one of the strands.
• A gene is a specific sequence of bases which has the information for a particular protein.
• DNA is self-replicating - it can make an identical copy of itself.
• Replication allows the genetic information to pass faithfully to the next generation.
• Replication occurs during the ‘S’ (= synthesis) stage of interphase just before nuclear division.
• The chromosomes contain 90% of the cell’s DNA.
• 10% is present in mitochondria and chloroplasts.
• Adenine (A) and Guanine (G) are purine bases
• Thymine (T) and Cytosine (C) are pyrimidine bases
• Hydrogen bonds link the complementary base pairs
• Two between A and T (A = T)
• Three between G and C (G ≡ C)
• A single unit in the chain is a nucleotide.
• This consists of a phosphate group,
• a pentose sugar (D = DNA; R = RNA) and
• an organic base (ATGC = DNA; AUGC = RNA)
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