nucleic acids

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  • Created on: 29-05-13 00:14

DNA and RNA

DNA - Deoxyribonucleic Acid - A, G, C and T - sugar deoxyribose

RNA - Ribonucleic Acid - A, G, C and U - sugar ribose

Made of chains of nucleotides which make polynucleotides, joined by covalent bonds between phosphate and sugar molecules to form a 'backbone'.

Nucleotide - Made of pentose sugar (5 Carbon Atoms), Phosphate, Nitrogenous Base.

Bases - Purines (Adenine and Guanine, double ring of carbon and Nitrogen atoms) and Pyramidines (Thymine, Cytosine and Uracil, single ring...).

DNA is a Double Helix - Made of two polynuecleotides held togther by H bonds, arranged so Purine is opposite Pyramidine (A:T, G:C), A+T have 2 H bonds, G+C have 3 H bonds, the two polynucleotides are antiparallel.

DNA is stable info is stored for a long time, large molecule stores lots of info, two polynucleotides act as template for synthesis of new polynucleotide during replication.

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DNA Replication + Protein Synthesis

Half the parent DNA molecule is passed onto the daughter molecule.

  • Double helix unwinds, DNA 'unzips' so hydrogen bonds between polynucleotides are broken.
  • Original polynucleotides act as templates for assembly of nucleotides. 
  • Free nucleotides, made in cytoplasm, move towards the exposed bases of DNA.
  • Base pairing occurs and hydrogen bonds form between complementary bases.
  • Enzyme DNA polymerase forms covalent bonds between free nucleotides attached to each template.
  • Two daughter DNA molecules form seperate double helixes, each with one parent strand.

DNA contains genes which are instructions for proteins. 

  • A gene is a sequence of DNA nucleotides that codes for a protein. Different proteins have a different number and order of amimo acids. 
  • Order of nucleotides determines order of amino acids. Three bases code for an amino acid.
  • DNA is copied into RNA in the nucleus. RNA leaves nucleus through nuclear pores to ribosome as mRNA. Then tRNA bring amino acids to the ribosome in the correct order, according to base sequence. Amino acids are joined by peptide bonds to form proteins.
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