Genetic Code , tRNA and rRNA

1. GeneticCode, tRNAandrRNA YILDIRIM BEYAZIT UNIVERSITY FACULTY OF MEDICINE THE DEPARTMENT OF MEDICAL BIOLOGY ASST. PROF. DR. ENDER ŞİMŞEK

2. The Genetic Code • Correspondence between the sequence of bases in a codon and the amino acid residue it specifies.

3. The Genetic Code • Correspondence between the sequence of bases in a codon and the amino acid residue it specifies. • 4 possible bases (U, C, A, and G) can occupy three positions of codon, therefore 43 = 64 possible codons.

4. The Genetic Code • Correspondence between the sequence of bases in a codon and the amino acid residue it specifies. • 4 possible bases (U, C, A, and G) can occupy three positions of codon, therefore 43 = 64 possible codons. • 61 codons specify amino acids, and 3 codons (UAA, UAG, and UGA)are stop codons (cause ribosome to end polypeptide synthesis and release the transcript).

5. Properties of the Genetic Code • The genetic code is composed of nucleotide triplets.

6. Properties of the Genetic Code • The genetic code is composed of nucleotide triplets. • The genetic code is non-overlapping.

7. Properties of the Genetic Code • The genetic code is composed of nucleotide triplets. • The genetic code is non-overlapping. • The genetic code is comma-free.

8. Properties of the Genetic Code • The genetic code is composed of nucleotide triplets. • The genetic code is non-overlapping. • The genetic code is comma-free. • The genetic code is degenerate.

9. Properties of the Genetic Code • The genetic code is composed of nucleotide triplets. • The genetic code is non-overlapping. • The genetic code is comma-free. • The genetic code is degenerate. • The genetic code is ordered. (5’ to 3’)

10. Properties of the Genetic Code • The genetic code is composed of nucleotide triplets. • The genetic code is non-overlapping. • The genetic code is comma-free. • The genetic code is degenerate. • The genetic code is ordered. (5’ to 3’) • The genetic code contains start and stop codons.

11. Properties of the Genetic Code • The genetic code is composed of nucleotide triplets. • The genetic code is non-overlapping. • The genetic code is comma-free. • The genetic code is degenerate. • The genetic code is ordered. (5’ to 3’) • The genetic code contains start and stop codons. • The genetic code is nearly universal.

12. Initiation and termination Codons • Initiation codon: AUG • Termination codons: UAA, UAG, UGA

13. Key Points • Each of the 20 amino acids in proteins is specified by one or more nucleotide triplets in mRNA. (20 amino acids refers to what is attached to the tRNAs!)

14. Key Points • Each of the 20 amino acids in proteins is specified by one or more nucleotide triplets in mRNA. (20 amino acids refers to what is attached to the tRNAs!) • Of the 64 possible triplets 61 specify amino acids and 3 signal chain termination. (have no tRNAs!)

15. Key Points • The code is non-overlapping, with each nucleotide part of a single codon, degenerate, with most amino acids specified by two to four codons, and ordered, with similar amino acids specified by related codons.

16. Key Points • The code is non-overlapping, with each nucleotide part of a single codon, degenerate, with most amino acids specified by two to four codons, and ordered, with similar amino acids specified by related codons. • The genetic code is nearly universal; with minor exceptions, the 64 triplets have the same meaning in all organisms.

17. Key Points • All but two amino acids (Met, Trp) are specified by more than one codon. • Three (Leu, Ser, Arg) are specified by six codons.

18. Key Points • All but two amino acids (Met, Trp) are specified by more than one codon. • Three (Leu, Ser, Arg) are specified by six codons. • Synonyms-multiple codons can code the same amino acid. • tRNA may recognize up to 3 synonymous codons because the 5’ base of a codon and 3’ base of the anticodon can interact in ways other than via Watson-Crick base pairs.

19. Key Points • All but two amino acids (Met, Trp) are specified by more than one codon. • Three (Leu, Ser, Arg) are specified by six codons. • Synonyms-multiple codons can code the same amino acid. • tRNA may recognize up to 3 synonymous codons because the 5’ base of a codon and 3’ base of the anticodon can interact in ways other than via Watson-Crick base pairs. • Translation is initiated at the AUG codon (Met) but this tRNA differs from the tRNA for internal amino acid the Met codon.

20. The Genetic Code

23. The Genetic Code Degeneration

24. Natural Changes of GeneticCode

25. Nucleotide reading frames:

26. The Wobble Hypothesis:Base-Pairing Involving the Third Base of the Codon is Less Stringent.

28. Inosine and Wobble Base

29. Base-Pairing with Inosineat the Wobble Position

30. Inosine

31. Inosine

32. Adenin (A), Guanin (G), Sitozin (C), Urasil (U), İnosin (I)

33. Tosynthesize protein: • mRNA • Ribosomes • tRNA’s • Amino acids • Enzymes

34. Ribosomes & rRNA’s S: Svedberg unit S: Svedberg unit

37. Transfer RNAs (tRNAs) • tRNAs are adapters between amino acids and the codons in mRNA molecules. • The anticodon of the tRNA base pairs with the codon of mRNA. • The amino acid is covalently attached to the 3’ end of the tRNA.

38. Specificity of tRNAs • tRNA molecules must have the correct anticodon sequence. • tRNA molecules must be recognized by the correct aminoacyl-tRNAsynthetase. • tRNA molecules must bind to the appropriate sites on the ribosomes.

39. Codon and Anticodon

40. tRNA Binding Sites on the Ribosome (Ribosomemoves like an enzyme)