Genetics - 03 Protein synthesis


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A closer look at protein synthesis for Year 10 students at Saint Ignatius College Geelong

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Genetics - 03 Protein synthesis

  1. 1. GENETICS. 03. Protein synthesis. Ian Anderson Saint Ignatius College Geelong
  2. 2. PROTEINS.  Proteins are polymers built up of amino acid monomers.  Proteins play a key role in living organisms.  They have specific roles.  Structural e.g. collagen, keratin.  Regulatory e.g. insulin, glucagon, adrenalin.  Enzymes e.g. amylase, pepsin.  Transport e.g. haemoglobin.  Each cell contains several hundred to several thousand proteins.  Human proteome estimated >100 000.
  3. 3. PROTEINS. Everything a cell is or does depends on the proteins it contains. Source:
  4. 4. PROTEIN SYNTHESIS.  DNA carries the sets of instructions in the chromosomes for every part of an organism, including the production of proteins.  Proteins however are manufactured on ribosomes located in the cell cytoplasm.  So a method is needed to transfer the information needed to build a protein from the DNA to the ribosomes.
  5. 5. PROTEIN SYNTHESIS.  DNA stays in the nucleus and another molecule, acting as a messenger, carries the instructions from the DNA to the ribosomes.  Proteins can now be manufactured by the ribosomes.  This two stage process = protein synthesis.
  6. 6. PROTEIN SYNTHESIS. Two stages of protein synthesis  Transcription  Translation
  7. 7. TRANSCRIPTION. Messenger RNA (mRNA) is made.  A single-stranded ‘copy’ of the DNA segment that codes for the required protein.  Steps: 1. Relevant segment of DNA unwinds forming two single strands. 2. Free floating nucleotides in nucleus bind to one strand following the base pairing rule.  adenine  uracil (not thymine)  cytosine  guanine 3. Complementary copy of DNA, called messenger RNA (mRNA) is formed.
  8. 8. DNA V RNA. DNA RNA Contains the sugar deoxyribose Contains the sugar ribose Contains the bases • Adenine (A) • Cytosine (C) • Guanine (G) • Thymine (T) Contains the bases • Adenine (A) • Cytosine (C) • Guanine (G) • Uracil (U) A double-stranded molecule • Has a double helix shape A single-stranded molecule Found in the cell nucleus [also found in mitochondria and chloroplasts] Three types • mRNA • tRNA • rRNA
  9. 9. TRANSCRIPTION. Source:
  10. 10. TRANSCRIPTION. Source:  The‘message’ from the DNA can now translated.
  11. 11. TRANSLATION. The synthesis of a protein from mRNA.  Steps: 1. mRNA leaves the nucleus and travels into cytoplasm and attaches to a ribosome.  Each sequence of three bases on the mRNA is called a codon (triplet code) and codes for a particular amino acid. 2. Transfer RNA (tRNA) molecule with a complementary base triplet (called an anticodon) carries specified amino acid to ribosome. 3. Amino acids are linked with peptide bonds to form a polypeptide.
  12. 12. DECIPHERING THE GENETIC CODE.  During translation the mRNA is read in sets of three nucleotides (codons).  There are more different combinations of codons than what there are naturally occurring amino acids.  All possible combinations of the four bases (A, C, G, U) result in 64 (43) three letter codons.  20 naturally occurring amino acids.  Meaning that there are more than one codon for most amino acids i.e.  e.g. CUU, CUC, CUA & CUG all code for the amino acid Leucine.
  13. 13. TRANSLATION. Source:
  14. 14. PROTEIN SYNTHESIS. Head on over to And make your own protein!
  15. 15.