The document discusses protein synthesis which begins with DNA carrying the code for amino acid sequences. During transcription, a copy of the DNA sequence is made into messenger RNA (mRNA) which then leaves the nucleus. During translation, transfer RNA (tRNA) molecules bring amino acids to the ribosome based on complementary base pairing between the tRNA anticodon and mRNA codons. Amino acids are joined by peptide bonds to form the polypeptide chain.

1. PROTEIN SYNTHESIS Made with copyright free images from Wikimedia

2. Amino acids Sequence of amino acids is important Peptide bond Protein / Polypeptide A chain of amino acids Linked by peptide bonds

3. The sequence of amino acids is important

4. The sequence of amino acids is important

5. DNA Carries information about the sequence of amino acids in proteins.

6. The sequence of bases in DNA is directly related to The sequence of amino acids in proteins

7. non-template strand A T T A G G C T A T A A T C C G A T template strand The Genetic Code Only one of the DNA strands carries the code – template strand

8. Sequence of 3 bases Codes for one amino acid Called a triplet The Genetic Code

9. DNA A T T A G G C T A (non-template strand) T A A T C C G A T (template strand) Amino acids The Genetic Code

10. Problem: DNA located : in the nucleus But proteins made : in cytoplasm at ribosomes

11. DNA is too large to leave the nucleus So… A ‘copy’ of the relevant section of DNA is made Forming a molecule of messenger RNA (mRNA) Then mRNA leaves the nucleus and travels to the ribosome

12. Protein Synthesis 1.Transcription DNA is used as a template to produce a molecule of mRNA 2.Translation the mRNA is used as a code to produce the chain of amino acids. occurs in the nucleus occurs in the cytoplasm

14. Transcription Transcription factors attach to a promoter region of DNA upstream of the gene to be transcribed This enables RNA polymerase to bind to the DNA at the start of the gene RNA polymerase passes along the DNA causing it to unwind and unzip – breaking hydrogen bonds between bases

15. Transcription RNA nucleotides attach to the exposed bases on the template strand by complementary base pairing RNA polymerase enables these nucleotides to attach to each other to form mRNA This initial molecule of mRNA is the primary transcript

17. single stranded contains uracil and not thymine contains ribose not deoxyribose each sets of 3 bases called codons mRNA

18. mRNA leaves the nucleus via a nuclear pore

19. mRNA is edited by splicing

20. Translation occurs in the cytoplasm mRNA associates with a ribosome

21. Also in the cytoplasm are tRNA’s (transfer RNA’s) tRNA’s carry specific amino acids to the ribosome Translation

23. tRNA At one end : a set of 3 unpaired bases called the anticodon The other end : an amino acid binding site binds to specific amino acids depending on the anticodon

24. mRNA attaches to the ribosome Translation

25. A tRNA with a complementary anticodon lines up against the first codon on the mRNA Translation

27. Translation

28. A second tRNA bonds with the next codon Translation

29. Translation

30. A peptide bond forms between the 2 amino acids Ribosome now moves 1 codon along the mRNA Translation

31. Translation

32. The first tRNA leaves returns to cytoplasm to attach to another amino acid A third tRNA brings the next amino acid Translation

33. Translation

34. The ribosome continues to move along the mRNA until the polypeptide chain is complete. Translation

35. Translation

37. SUMMARY SUMMARY

38. Exam Questions

39. More likely to get this

40. Sequence of bases is the code ; DNA strands separate /Hydrogen bonds break ; producing mRNA/transcription (linked to mRNA production) ; role of RNA polymerase ; complementary base pairing ; mRNA attaches to ribosome/RER ; tRNA bring amino acid ; anticodons of tRNA complementary to codons on mRNA ; amino acids join by peptide bonds/condensation reaction ; Than this

41. Features of the Genetic Code

42. The Genetic Code is a : Degenerate code Each amino acid is coded for by more than one set of triplet bases Because… Proteins are made from 20 different amino acids 64 different combinations of triplet bases

44. The Genetic code is : Non-overlapping Each base is only used once to code for an amino acid Universal The same triplet of bases codes for the same amino acid in every organism

45. Control: Promoters and Transcription factors A promoter is a region of DNA that aids the transcription of a gene. Promoters are typically located near the genes they regulate, on the same strand and upstream a transcription factor is a protein that binds to a promoter region and thereby initiates the process of transcription. It does this by facilitating the binding of RNA polymerase.

46. Control: Promoters and Transcription factors

47. Control: Promoters and Transcription factors

48. Control: The example you have to learn - Effect of oestrogen on transcription Oestrogens : a group of steroid hormones – roles include development of secondary sexual characteristics and are involved in the regulation of the oestrus cycle.

49. Control: The example you have to learn - Effect of oestrogen on transcription Oestrogen enters the cell Oestrogen binds to receptor molecules in the cytoplasm

50. Control: The example you have to learn - Effect of oestrogen on transcription And promote the transcription of these genes They enter the nucleus & bind to promoter regions The oestrogen-receptor complexes act as transcription factors

51. Control: Mechanism of RNA interference (RNAi). The appearance of double stranded RNA [usually as a result of viral infection] can start the process. The enzyme Dicer [blue] binds to the double stranded RNA and cleaves it into short pieces of approx. 20 base pairs in length known as small interfering RNA (siRNA) [orange-red].

52. The siRNA binds to a protein called “RNA-induced silencing complex” (RISC) – this protein splits the siRNA one strand remains and RISC uses one strand of the siRNA to bind to mRNA molecules. The nuclease activity of RISC then breaks down the mRNA stopping it being translated. Control: Mechanism of RNA interference (RNAi).