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BIOLOGY PRESENTATIONS FOR A-LEVEL, IN MULTIMEDIA JAMES BOWLES, 2001. LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END. ‘A’ Level Biology. Protein Synthesis. The Genetic Code. The sequence of bases determines the order of amino acids in a protein.
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BIOLOGY PRESENTATIONS FOR A-LEVEL, IN MULTIMEDIA JAMES BOWLES, 2001 LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END
‘A’ Level Biology Protein Synthesis
The Genetic Code The sequence of bases determines the order of amino acids in a protein
The Genetic Code The code is read in Triplets of bases U A A G C G U A U U G G C A U This gives 64 combinations of the 4 bases
The Genetic Code Each triplet is read as a discrete unit U A A G C G U A U U G G C A U It is a non-overlapping code
G U U G U C • G U A G U G The Genetic Code It is a Degenerate code Valine Most amino acids have more than one triplet coding for them
U A A • U A G U G A The Genetic Code There is also punctuation in the code Stop code
Codons code for the same amino acid in all organisms The Genetic Code The code is universal
Protein Synthesis Protein synthesis occurs in three stages: • Transcription • Activation of Amino Acids • Translation
Transcription Part of the DNA molecule unwinds
Transcription RNA polymerase attaches at a start codon
Transcription RNA polymerase moves along the DNA catalysing the production of mRNA
Transcription At the stop codon the RNA polymerase and mRNA detach from the DNA
Activation of Amino Acids Met Amino Acids combine with tRNA U A C
Activation of Amino Acids Met This process utilises specific enzymes and ATP is hydrolysed U A C
A U G G C G U A U U G G C A U Translation A ribosome attaches to a length of mRNA
Met Met Met Met Met U A C U A C U A C U A C U A C A U G G C G U A U U G G C A U Translation tRNA with corresponding anticodon fits in the ribosome
Ala Ala Ala Met Ala C G C C G C C G C C G C U A C A U G G C G U A U U G G C A U Translation A second piece of tRNA fits into the ribosome
Met C G C U A C A U G G C G U A U U G G C A U Translation Ala A peptide bond forms between the amino acids
Met U A C C G C A U G G C G U A U U G G C A U Translation The ribosome moves along one codon Ala C G C
U A C U A C U A C C G C A U G G C G U A U U G G C A U Translation Met Ala The first piece of tRNA is released C G C
C G C A U G G C G U A U U G G C A U Translation Met Ala The 1st amino acid remains in place C G C
Tyr Tyr Tyr Tyr A U A A U A A U A A U A C G C A U G G C G U A U U G G C A U Translation Met Ala The process is repeated C G C