Nucleic Acids - DNA and RNA Unit 2 OCR

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  • Created on: 30-05-13 16:13
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  • Nucleic Acids
    • DNA
      • Function - contains your genetic information, all the instructions needed to grow and develop from fertilised egg to fully grown adult
      • Structure - double helix, formed from two separate strands that wind around each other to form a spiral, strands are polynucleotides made up of lots of nucleotides joined in a long chain, really long and tightly coiled so lots of genetic information fits into small space in nucleus
        • Nucleotide  Structure - made from phosphate group pentose sugar with 5 carbon atoms and a nitrogenous base, sugar in DNA nucleotide is deoxyribose, each has the same sugar and phosphate, base can vary though
          • 4 based - Adenine, Thymine, Cytosine, Guanine
            • A and G make purine base, C and T make pyrimidines base
        • Polynucleotide Structure - many nucleotides join to form polynucleotide strands, they join between phosphate group and sugar creating a sugar phosphate backbone
      • Complimentary Base Pairing
        • Two polynucleotide strands join be hydrogen bonds between bases, each base can only join with one particular partner
        • Adenine always pairs with Thymine and Guanine always pairs with Cytosine meaning that purine always pairs with pyrimidine
          • Two H bonds form between A and T, Three H bonds form between C and G
        • Two polynucleotides strands are anti-parallel = run in the opposite direction, the anti-parallel strands twist to form DNA double-helix
      • Replication
        • Why - copies before cell division so each new cell has the full amount of DNA so is important in making new cells and passing genetic information to generations
        • 1. Hydrogen bonds between two polynucleotide DNA strands break, the helix unzips to form single strands
          • 2. Each original single strand acts as template for new strand, free floating DNA nucleotides join to exposed bases on original by complimentary base pairing
            • 3. Nucleotide on new strand joined together by enzyme DNA polymerase, H bonds form between bases on original and new strand, each new DNA contains one original and one new strand
        • Semi conservative replication - half of new strand is from original
    • RNA
      • Function - similar in structure to DNA, several different types of RNA each with different function = one main type is mRNA used to make proteins from instructions contained within DNA
      • Structure - made up of nucleotides that contain one of four different bases, also form a polynucleotide strand with a sugar phosphate back bone but the structure differs in three main ways
        • The sugar in RNA is ribose sugar but is still a pentose sugar
        • Nucleotides form a single polynucleotide strand not a double
        • Uracil replaces thymine as a base and always pairs with Adenine
    • Protein Synthesis
      • Genes - DNA contains genes : sequence of DNA nucleotides that code for a protein (polypeptide)
        • Proteins made from amino acids, different proteins have different number and order of amino acids, it's the order of nucleotide bases in a gene that determine order of amino acids in particular protein
          • Each amino acid coded for by sequence of three bases in a gene, different sequences of bases code for different amino acids
      • Gene Mutations - changes in the base sequence of organisms DNA, if base sequence in a gene is changed the sequence of amino acids in protein it codes for may also change
        • May affect the way the protein folds up and so its overall 3D shape, as a result a different or non-functional protein could be produced
      • DNA, RNA and Protein Synthesis
        • All reactions and processes n living organisms need protein - DNA caries instructions to make protein so is vital for protein synthesis but RNA also plays a key role
        • DNA found in nucleus of cell, ribosomes assemble proteins and are found in cytoplasm, DNA is too large to leave nucleus so a section is copied into mRNA
          • The mRNA leaves the nucleus and joins with a ribosome in cytoplasm where it can be used to synthesise a protein


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