Biology AS - DNA

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DNA Structure:

  • DNA: Double polynucleotide chains
  • Sugar–phosphate backbone
  • Deoxyribose Sugar joined to a Phosphate by a Phosphodiester bond
  • Bases ( Thymine, Adening, Guanine and Cytosine) bonded together with Hydrogen Bonds

RNA Structure:

  • RNA: Single polynucleotide chain
  • Phosphate
  • Ribose Sugar
  • Base: Uracil, Adenine, Guanine and Cytosine

- Purine (two carbon-nitrogen rings) – e.g. Adenine & Guanine

- Pyrimidines (one carbon-nitrogen ring) – e.g. Cytosine, Thymine & Uracil

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Semi Conservative Replication:

Semi Conservative Replication:

  • The enzyme Helicase splits the DNA, which allows free bases in the surrounding solution to bond and form two new strands of DNA – with one original chain and one new chain
  • The enzyme, Polymerase, is then used to form Phosphodiester bonds – this forms sugar phosphate backbone

ADP has a 2 phosphates, Ribose Sugar and Adenine

  • When energy is used, a new Phosphate bonds with a Phosphate bond and forms ATP 
  • Energy is stored in Phosphate bond and can be released to provide energy
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tRNA and rRNA

rRNA Molecule:

  • Catalyses formation of peptide bonds
  • Large subunit
  • Small subunit

tRNA Molecule: 

  • Anticodon (3 bases)
  • Intramolecular base pairings with Hydrogen bonds between
  • Bonded together with a Amino Acid using a Ester Bond

Genetic Code:

  • Base triplets (codons) code specific amino acids – non-overlapping
  • Degrading genetic information: coded for by more than one codon
  • Universal: same codons in all living things
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Tranbscription and Translation

- Polymerase unravels the DNA – one stand will be used as a template for mRNA

- Free RNA Nucleotides line up and form a complementary strand of mRNA

- This continues along the length of the DNA – hydrogen bonds reform and the DNA is put back together

- mRNA strand moves into Cytoplasm and joins to the tRNA and form Peptide bonds between Amino Acids – forms a protein

- tRNA then moves away, leaving a chain of Amino Acids

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