Nucleic Acids

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Nucleic Acids Protein Synthesis

• Chapter 3

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Structure of DNA

• Chromosomes are composed of DNA
• - deoxyribonucleic acid
• DNA is double stranded
• Each strand made of nucleotides
• Nucleotides are made of a deoxyribose sugar, a
  phosphate group and a base
• Bases adenine (A), guanine (G), cytosine (C),
  thymine (T)
• Strong chemical bonds between phosphates sugars
  join nucleotides
• Hydrogen bonds join bases from one strand to a
  complimentary base on the other strand (A-T, G-C)
• This forms a double helix (spiral ladder)

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Structure of RNA

• Also consists of nucleotides, BUT
• 1) Is single stranded (DNA is double stranded)
• 2) Has the base uracil (U) (instead of thymine
  (T))
• 3) Has a ribose sugar (instead of deoxyribose)

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DNA base sequence

• Order quantity of DNA bases establishes
  differences between living things
• Protein structure/function is dependant upon
  amino acid sequence
• Amino acid sequence depends on DNA base sequence
  genetic code
• Every 3 bases of DNA will correspond to a
  particular amino acid

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Protein Synthesis

• Proteins are made in the cytoplasm
• A messenger is required to pass information from
  the DNA to the cytoplasm
• This is messenger RNA (mRNA)
• It is formed (transcribed) from free RNA
  nucleotides in the nucleus
• This process of transcription involves 8 stages

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Transcription of DNA into mRNA

• 1) DNA double helix unwinds
• 2) H bonds between bases start to break
• 3) Free RNA nucleotides pair with their
  complimentary DNA nucleotides
• 4) H bonds form between RNA and DNA
• 5) An enzyme (RNA polymerase) helps to join RNA
  nucleotides
• 6) mRNA separates from DNA template
• 7) mRNA leaves the nucleus through a pore in the
  nuclear membrane
• 8) H bonds reform to reunite the DNA chains
  double helix reforms

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Translation (RNA to protein)

• mRNA leaves the nucleus and moves to the
  cytoplasm
• mRNA becomes attached to a ribosome
• The mRNA is then translated to form a protein
• Transfer RNA (tRNA) is found in the cytoplasm
• tRNA has triplets of bases - ANTICODONS
• Each triplet corresponds to a certain amino acid
• Anticodons match up with the codons on the mRNA
• tRNA then brings each amino acid in sequence
• Amino acids then joined by peptide bonds

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Translation Video Clip
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Cell Structure

• Nucleolus Within the nucleus made of DNA, RNA
  protein (help to make ribosomes)
• Ribosome found in cytoplasm translation of
  mRNA into protein
• Free ribosomes protein stays inside cell
• Attached to Endoplasmic Reticulum (ER) proteins
  out of cell

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Cell Structure

• Endoplasmic Reticulum (ER)
• Rough ER Encrusted with ribosomes
• - pathway for transport of materials
• - proteins synthesised on ribosome, injected into
  ER, coiled folded
• - passed on for exiting the cell
• Smooth ER no ribosomes
• - Various roles site of many reactions

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Cell Structure

• Golgi Apparatus
• Picks up proteins from rough ER (in vesicles)
• Proteins processed, passed through (in
  vesicles)
• Vesicles with finished product are pinched off
  from the end discharged out of cell
• This is called exocytosis
• Lysosomes vesicles containing digestive enzymes
  (cell repair and cell defence)

Golgi Apparatus