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  1. 1. PROTEIN SYNTHESIS Made with copyright free images from Wikimedia
  2. 2. Amino acids Sequence of amino acids is important Peptide bond Protein / Polypeptide <ul><li>A chain of amino acids </li></ul><ul><li>Linked by peptide bonds </li></ul>
  3. 3. The sequence of amino acids is important
  4. 4. The sequence of amino acids is important
  5. 5. DNA <ul><li>Carries information about </li></ul><ul><li>the sequence of amino </li></ul><ul><li>acids in proteins. </li></ul>
  6. 6. <ul><li>The sequence of bases in DNA </li></ul><ul><li>is directly related to </li></ul><ul><li>The sequence of amino acids in proteins </li></ul>
  7. 7. <ul><li>non-template strand </li></ul><ul><li>A T T A G G C T A </li></ul><ul><li>T A A T C C G A T </li></ul><ul><li>template strand </li></ul>The Genetic Code <ul><li>Only one of the DNA strands carries the code – template strand </li></ul>
  8. 8. <ul><li>Sequence of 3 bases </li></ul><ul><li>Codes for one amino acid </li></ul><ul><li>Called a triplet </li></ul>The Genetic Code
  9. 9. <ul><li>DNA </li></ul><ul><li>A T T A G G C T A (non-template strand) </li></ul><ul><li>T A A T C C G A T (template strand) </li></ul><ul><li>Amino acids </li></ul>The Genetic Code
  10. 10. Problem: <ul><li>DNA located : </li></ul><ul><li>in the nucleus </li></ul><ul><li>But proteins made : </li></ul><ul><li>in cytoplasm at ribosomes </li></ul>
  11. 11. <ul><li>DNA is too large to leave the nucleus </li></ul><ul><li>So… </li></ul><ul><li>A ‘copy’ of the relevant section of DNA is made </li></ul><ul><li>Forming a molecule of messenger RNA (mRNA) </li></ul><ul><li>Then </li></ul><ul><li>mRNA leaves the nucleus </li></ul><ul><li>and travels to the ribosome </li></ul>
  12. 12. Protein Synthesis <ul><li>1.Transcription </li></ul><ul><li>DNA is used as a template to produce a </li></ul><ul><li>molecule of mRNA </li></ul><ul><li>2.Translation </li></ul><ul><li>the mRNA is used as a code to produce the </li></ul><ul><li>chain of amino acids. </li></ul>occurs in the nucleus occurs in the cytoplasm
  13. 14. Transcription <ul><li>Transcription factors attach to a promoter region of DNA upstream of the gene to be transcribed </li></ul><ul><li>This enables RNA polymerase to bind to the DNA at the start of the gene </li></ul><ul><li>RNA polymerase passes along the DNA causing it to unwind and unzip – breaking hydrogen bonds between bases </li></ul>
  14. 15. Transcription <ul><li>RNA nucleotides attach to the exposed bases on the template strand by complementary base pairing </li></ul><ul><li>RNA polymerase enables these nucleotides to attach to each other to form mRNA </li></ul><ul><li>This initial molecule of mRNA is the primary transcript </li></ul>
  15. 17. <ul><li>single stranded </li></ul><ul><li>contains uracil and not thymine </li></ul><ul><li>contains ribose not deoxyribose </li></ul><ul><li>each sets of 3 bases called codons </li></ul>mRNA
  16. 18. mRNA leaves the nucleus via a nuclear pore
  17. 19. mRNA is edited by splicing
  18. 20. Translation <ul><li>occurs in the cytoplasm </li></ul><ul><li>mRNA associates with a ribosome </li></ul>
  19. 21. <ul><li>Also in the cytoplasm are </li></ul><ul><li>tRNA’s (transfer RNA’s) </li></ul><ul><li>tRNA’s carry specific amino acids to the ribosome </li></ul>Translation
  20. 23. tRNA <ul><li>At one end : </li></ul><ul><li>a set of 3 unpaired bases called the anticodon </li></ul><ul><li>The other end : </li></ul><ul><li>an amino acid binding site </li></ul><ul><li>binds to specific amino acids </li></ul><ul><li>depending on the anticodon </li></ul>
  21. 24. <ul><li>mRNA attaches to the ribosome </li></ul>Translation
  22. 25. <ul><li>A tRNA with a complementary anticodon </li></ul><ul><li>lines up against </li></ul><ul><li>the first codon on the mRNA </li></ul>Translation
  23. 27. Translation
  24. 28. <ul><li>A second tRNA bonds with the next codon </li></ul>Translation
  25. 29. Translation
  26. 30. <ul><li>A peptide bond forms between the 2 amino acids </li></ul><ul><li>Ribosome now moves 1 codon along the mRNA </li></ul>Translation
  27. 31. Translation
  28. 32. <ul><li>The first tRNA leaves </li></ul><ul><li>returns to cytoplasm to attach to another amino acid </li></ul><ul><li>A third tRNA brings the next amino acid </li></ul>Translation
  29. 33. Translation
  30. 34. <ul><li>The ribosome continues to move along the mRNA until the polypeptide chain is complete. </li></ul>Translation
  31. 35. Translation
  33. 38. Exam Questions
  34. 39. More likely to get this
  35. 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
  36. 41. Features of the Genetic Code
  37. 42. The Genetic Code is a : <ul><li>Degenerate code </li></ul><ul><li>Each amino acid is coded for by more than one set of triplet bases </li></ul><ul><li>Because… </li></ul><ul><li>Proteins are made from 20 different amino acids </li></ul><ul><li>64 different combinations of triplet bases </li></ul>
  38. 44. The Genetic code is : <ul><li>Non-overlapping </li></ul><ul><li>Each base is only used once to code for an amino acid </li></ul><ul><li>Universal </li></ul><ul><li>The same triplet of bases codes for the same amino acid in every organism </li></ul>
  39. 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.
  40. 46. Control: Promoters and Transcription factors
  41. 47. Control: Promoters and Transcription factors
  42. 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.
  43. 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
  44. 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
  45. 51. Control: Mechanism of RNA interference (RNAi). <ul><li>The appearance of double stranded RNA [usually as a result of viral infection] can start the process. </li></ul><ul><li>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]. </li></ul>
  46. 52. <ul><li>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. </li></ul><ul><li>The nuclease activity of RISC then breaks down the mRNA stopping it being translated. </li></ul>Control: Mechanism of RNA interference (RNAi).