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Protein Synthesis

Protein synthesis is a vital process in every cell, performing multiple roles in biological processes. This article explains the importance of protein and how it is synthesized through transcription and translation.

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Protein Synthesis

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  1. Protein Synthesis (TRANSLATION)

  2. Why is protein very important? It is the essential structural part of every cell It performs multiple important roles in all biological processes. No life without protein How they are synthesised???

  3. Central Dogma

  4. Central Dogma http://cnx.org/content/m11415/latest/central_dogma.jpg

  5. The production of a protein molecule by a cell is the result of a two part process. Transcription Translation

  6. The transfer of genetic information from DNA to RNA is known as transcription.

  7. Transcription occurs in the nucleus of the eukaryotic cell 1) DNA strand separates and serves as a template (pattern) for mRNA assembly

  8. 2) free RNA nucleotides match up to the exposed nucleotides on the DNA strand

  9. mRNA strand leaves the DNA strand when a “stop signal” is reached the mRNA strand carries the code for the production of one polypeptide

  10. The second part of the process, called translation, occurs in the cytoplasm and results in the synthesis of a specific protein molecule from the genetic information carried by the mRNA.

  11. Translation occurs in the cytoplasm of the eukaryotic cell 1) mRNA moves out of the nucleus and into the cytoplasm to a ribosome 2) mRNA is “read” by the ribosome and is converted to a chain of amino acids with the help of tRNA

  12. Translation As the mRNA moves across the ribosome, tRNAs temporarily attach. The amino acids are joined by a chemical bond by enzymes until a stop codon is reached a polypeptide is produced

  13. DNA is transcribed to mRNA in the nucleus and mRNA is translated into Protein in the cytoplasm

  14. TRANSLATION • The mRNA are short lived and immediately translated. • In translation process proteins are synthesized.

  15. Protein Synthesis Material • RNA (mRNA, tRNAs, rRNAs) • Amino acids (20 common AA) • Ribosomes (rRNA+proteins) • Enzymes and protein factors • Cations ( Mg2+, K+) • Energy (ATP, GTP)

  16. RNA • RNA, like DNA, is a polymer formed by a sequence of nucleotides • Three main types of RNA: messenger RNA (mRNA)---template transfer RNA (tRNA)--- transfer amino acids ribosomal RNA (rRNA)---form ribosome with proteins, which provides place for translation

  17. mRNA ----As a template for protein synthesis. Initiation codon stop codon open reading frame, ORF Is it in prokaryotic or eukaryotic cells?

  18. 3 5 PPP protein 3 mG - 5 PPP protein UTR Site for ribosome binding CDS Initiation codon Stop codon Polycistronic mRNA in prokaryotes Monocistronic mRNA in eukaryotes ORF 目 录

  19. 4 nucleotides in mRNA ？ 20amino acids in protein 目 录

  20. 1961-1966，Nirenberg、Matthaeiand Khorana Identified 64genetic codon。 A sequence of 3 bases codes for one amino acid

  21. Genetic Codon (Triplet codon) It is a triplet code consisting of sequence of three nucleotides, which codes for a specific amino acid, or stands for initiation and stop signals. 149

  22. 64 genetic codons Initiation codon: AUG (Methionine) Stop codon: UAA UAG UGA 61 codons for 20 amino acids

  23. Third letter Genetic Codon

  24. Properties of Genetic Codon 1. Directionality mRNA protein N C

  25. Properties of Genetic Codon 2. Commaless (Non-punctuation and nonoverlapping) mRNA successively

  26. insertion deletion • Frame shift mutation One or two base in coding region change ( insertion or deletion)-------frame shift mutation Tyrosine Alanine Serine Proline Threonine

  27. Properties of Genetic Codon 3. Degeneracy Except Methionine and Tryptophan, every amino acid is encoded by more than one codon. 149

  28. AA Number of codon AA Number of codon 3. degeneracy 目 录

  29. 3. Degeneracy Gly GGU GGC GGA GGG 目 录

  30. 3. Degeneracy In general, the specificity of codon is determined by the first two letters, since the third letter is less important. If the third letter of genetic codon changes, it might not change the amino acid and affect the stucture of the synthesized protein.

  31. Properties of Genetic Codon 4. Universality The genetic codons are the same in almost all organisms with some rare exception( human mitochondrial mRNA) The universality indicates that all living things share a common evolutionary heritage.

  32. Properties of Genetic Codon 5. Wobble mRNA 5----------3  1 2 3 3 2 1 tRNA 3 ---------5  Related to the secondary structure of tRNA Cloverleaf codon anticodon

  33. Properties of Genetic Codon 5. Wobble mRNA 5----------3  1 2 3 3 2 1 tRNA 3 ---------5  codon anticodon Wobble often happens the base pairing of the third base of codonin mRNA with the first base of anticodon in tRNA.

  34. Wobble U U 目 录

  35. Wobble base pairing

  36. tRNAs 75–90 nucleotides long and contain some rarebases. Secondary structure of tRNAs is a cloverleaf. Tertiary structure is a inverted “L-shaped”

  37. tRNA Tertiary structure Secondary structure

  38. tRNA Act as adapter molecules that recognize both a codon and a spcific amino acid. There about 40 different tRNAs interact with 61 sense codons. Two crucial sites: Amino acid attachment site and mRNA binding site. mRNA Amino acid

  39. tRNA

  40. Ribosomes consist of ribosomal proteins and ribosomal RNAs (rRNAs). have a large subunit and a small subunit. http://image.wistatutor.com/content/feed/u2044/ribosomes%20%20function.jpg

  41. Ribosomal Units

  42. S is a subsidence  coefficient represent the size of rRNA and ribosome subsidence rate and resistance coefficient  subsidence rate and resistance coefficient Figure 15.1

  43. Ribosomes Small subunit can bind initiator tRNA and mRNA for initiaion. There are two binding sites: A site (binding incoming aminoacyl-tRNA) P site( binding the growing polypeptide chain) E site (only in prokaryotic ribosome, empty tRNA exit from this site)

  44. Structure model of prokaryotic ribosome in translation Small subunit Amino acid Polypeptide chain Large subunit P site: peptidyl site Asite： aminoacyl site E site： exit site 目 录

  45. During translation all the molecules like mRNA, tRNA, amino acids are brought together to the ribosomal surface.

  46. Studies for the structure and function of the ribosome ------The Nobel Prize in Chemistry, 2009 Thomas A. Steitz Ada E. Yonath Venkatraman Ramakrishnan

  47. Other factors involved in protein synthesis Three important enzymes Aminoacyl-tRNA synthetase : catalyze the binding of amino acid to corresponding tRNA. Peptidyl transferase: catalyze the formation a peptide bond between polypeptide in P site with amino acid in A site. Translocase: EF-G, drive ribosome move along to the 3 of mRNA for one codon.

  48. Other factors involved in protein synthesis Protein factors Initiation factor : IF and eIF( eukaryotes) Elongation factors: EF and eEF Release factors: RF and eRF Energy and Ions • Energy : ATP and GTP • Ions: Magnesium ions(Mg2+) and Potassium ions (K+)

  49. Amino acid activation Amino acid are present freely in the cytoplasm in the inactive state. Amino acid activation means the amino acid is attached to a corresponding tRNA. 149

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