Translation

1. Translation © 2007 Paul Billiet ODWS

2. The tRNA molecule • tRNA molecules do the final translating • At one end the have a specific amino acid attached by a tRNA activating enzymeThese enzymes do the first part of translating • At the other end they have an anticodon which is complementary to the mRNA codons © St Edward’s University: Dept Chemistry and Biochemistry © 2007 Paul Billiet ODWS

3. The 3-D structure of a tRNA © ThinkQuest.org

4. The genetic code Made of 64 triplets of bases (codons) © 2007 Paul Billiet ODWS

5. © 2007 Paul Billiet ODWS

6. The degenerate genetic code • A few amino acids are coded for by a single codon • Most are coded for by more than one codon • Some are coded for by up to six codons • This is degeneracy in the code © 2007 Paul Billiet ODWS

7. Grammar in the code? • Three codons are nonsense codons they represent the end of the information = STOP • The codon for methionine found at the beginning of the information to be transcribed it means START • The methionine amino acid is usually removed from the finished protein © 2007 Paul Billiet ODWS

8. © 2007 Paul Billiet ODWS

9. Genetic code: characteristics • Only 61 triplets or codons code for amino acids • 3 stop codons (aka nonsense codons or terminator codons) UUA UAG UGA © 2007 Paul Billiet ODWS

10. The code is degenerative code • Several codons code for the same amino acid • The first two letters seem to be the most important the third one tends to be interchangeable © 2007 Paul Billiet ODWS

11. Similar amino acids have similar codons ExampleAspartic acid codons GAU and GACGlutamic acid codons GAA and GAG Both are acidic amino acids © 2007 Paul Billiet ODWS

12. Punctuation? • The is no punctuationbetween each codon • The reading frame is set at the beginning of the gene • Frame shift mutations can be caused by the ADDITION or DELETION of only one or two bases. Everything downstream is misread © 2007 Paul Billiet ODWS

13. Reading the code • The reading of mRNA is always in the same direction 5’ to 3’ (the same way as transcription and replication) • The polypeptide chain is constructed from the amino end to the carboxyl end © 2007 Paul Billiet ODWS

14. A universal code • The code is used by all organisms • So it is very ancient • Permits investigations into common ancestry • Permits genetically transformed organisms © 2007 Paul Billiet ODWS

15. 20 is the limit • Some amino acids are chemically altered AFTER translation. e.g. In collogen proline is converted to hydroxyproline • Therefore the total number of amino acids found in proteins is greater than 20 but the total used in translation is only 20 © 2007 Paul Billiet ODWS

16. Translation plan Complete protein Polypeptide chain TRANSLATION Ribosomes Start codon Stop codon © 2007 Paul Billiet ODWS

17. AUGGGAUACACUUUUUGA Ribosome mRNA Translation1 © 2007 Paul Billiet ODWS

18. met amino acid tRNA anticodon UAC AUGGGAUACACUUUUUGA Translation 2 © 2007 Paul Billiet ODWS

19. CCU UAC AUGGGAUACACUUUUUGA gly met Translation 3 © 2007 Paul Billiet ODWS

20. peptide bond met gly CCU UAC AUGGGAUACACUUUUUGA Translation 4 © 2007 Paul Billiet ODWS

21. met gly tyr UAC CCU AUG AUGGGAUACACUUUUUGA Translation 5 © 2007 Paul Billiet ODWS

22. met gly tyr CCU AUG AUGGGAUACACUUUUUGA Translation 6 © 2007 Paul Billiet ODWS

23. met gly tyr UGA CCU AUG AUGGGAUACACUUUUUGA thr Translation 7 © 2007 Paul Billiet ODWS

24. polypeptide chain met gly tyr thr AAA AUG UGA AUGGGAUACACUUUUUGA phe Translation 8 © 2007 Paul Billiet ODWS

25. Translation: the sequence • The tRNA molecules with the correct anticodons are lined up with their bases complementary to the mRNA codons • Two tRNA molecules at a time can fit on the ribosome • A peptide bond forms between their amino acids • The first tRNA leaves the ribosome and mRNA move along to accept a new tRNA • The process of translation proceeds in the same direction as replication and transcription (5’ to 3’) © 2007 Paul Billiet ODWS