nucleotides

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  • nucleotides
    • DNA
      • deoxyribose nucleic acid
      • two strands of repeating units called nucleotides
        • two strands twisted into a double helix
      • controls sequence of amino acids in proteins
      • hereditary material responsible for passing genetic material on from cell to cell
      • stable, two strands can sperate
    • RNA
      • ribonucleic acid
      • single stranded
        • ribosomal RNA
          • decodes mRNA into amino acids
      • as uracil base instead of thymine
      • messenger RNA
        • strand that is complementary to one strand of the DNA molecule
      • transfer RNA
        • carries amino acids to the ribosomes where they are bonded together  into polypeptides
    • nucleotides
      • made up of: pentose sugar, nitrogenous base and a phosphate group, joined by covalent bonds
      • joining nucleotides together
        • a condensation reaction occurs between the phosphate group of one and the pentose sugar of another
      • purines (larger)
        • double rings of carbon and nitrogen atoms
        • e.g adenine and guanine
      • pyrimidines (smaller)
        • single ring of carbon and nitrogen atoms
        • e.g thymine, cytosine and uracil
      • complementary base pairing
        • adenine pairs with thymine
        • cytosine pairs with guanine
        • a  purine in one strand is always opposite a pyrimidine in another
        • held in place via hydrogen bonds
    • DNA replication
      • identical DNA produced
      • DNA helicase unzips and unwinds DNA, forming two seperate strands
      • free nucleotides complementary base pair to the exposed bases on the DNA strand
      • DNA polymerase joins the new nucleotides together by strong covalent bonds, forming the sugar phosphate backbone
      • semi conservative as one strand left over is always the original
    • Protein synthesis
      • trnascription
        • DNA unzips as hydrogen bonds break
        • one strand acts as a template, free RNA nucleotides complementary base pair to exposed bases on template DNA stand
          • RNA polymerase joins nucleotides to form sugar phospahte backbone
            • mRNA detatches from template strand
              • dna molecules wind back into a helix
      • translation
        • sequence of three bases on mRNA coding for a specific amino acid is called a codon
        • process by which mRNA is translated into a protein
        • after the mRNA has left the nucleus following transcription it goes into the cytoplasm to which a ribosome attatches
          • the genetic code on the mRNA is read in codons
            • tRNA molecules have specific anticodons for each of the amino aicds
              • complementary tRNA anti codon is attracted to the mRNA codon so weak hydorgen bonds are formed
                • this follows on for each codon and a peptide bond is formed between adjacent amino acids that have now been coded for
                  • a stop codon is then reached

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