Protein Biosynthesis (Translation),Zhongren Ding, MD, PhD Department of Biochemistry,Protein Biosynthesis,Protein biosynthesis: easy, you can do it! How is protein biosynthesized? Understand the process of protein synthesis, regulation and control with aim to interfere protein synthesis. Stop abnormal protein synthesis (tumor treatment). Inhibit bacteria protein synthesis, treat infectious diseases; Biosynthesis of protein drugs.,Not easy,Protein Chemical (Artificial) Synthesis,Chemical synthesis of crystalline bovine insulin (51 aa, Shanghai, China 1965） Chemical synthesis of peptide (mg kg, 140 aa, purity: 98, RMB100/aa),G13 blocking peptide inhibits human platelet aggregation and ATP release,Synthesized peptide AYPGKF 100 microM stimulates human platelet aggregation and ATP release in the presence of aspirin,Grasp the properties of genetic code; Familiar with the structure and function of mRNA, tRNA, and ribosome; Familiar with the process of protein synthesis in prokaryotes; Familiar with the process of protein synthesis in eukaryotes; Know protein folding, and clinical relevance of protein synthesis.,Purpose and Requirements,1. What is protein biosynthesis? Why also called translation? 2. Protein synthesis system (What is needed to synthesize protein) 3. Protein synthesis process 4. Posttranslational processing and targeting 5. Protein synthesis in medicine,Protein Biosynthesis,What is protein biosynthesis? Why also called translation?,A process in which amino acids are synthesized into polypeptide in ribosomes using mRNA as template; also includes folding, posttranslational processing, transportation. In protein synthesis, the genetic information present in mRNA is transformed into the sequence of amino acids of the corresponding specific protein, similar to the process one language translated into another language, so its also called “translation”.,1. What is protein biosynthesis? Why also called translation? 2. Protein synthesis system (What is needed to synthesize protein) 3. Protein synthesis process 4. Posttranslational processing and targeting 5. Protein synthesis in medicine,Protein Biosynthesis,Amino acids: materials mRNA: template, consisting of genetic codes tRNA: transfer tool and adaptor Ribosome: workplace Protein factors Synthetic enzymes,2. Protein synthesis system (What is needed to synthesize protein?),2. Protein synthesis system,2.1 Genetic code defines the relationship between the base sequence of mRNA and the amino acid sequence of polypetide Three bases needed to specify one amino acid, because: 1) 4 bases need to code 20 amino acids, 2) 41 = 4, 42 = 16, 43 = 64 The 3 bases triplets on mRNA (and DNA) coding for a specific amino acid is called genetic codes.,Sydney Brenner (1927 - ) 2002 Nobel Prize Laureate,Genetic Codes and its prominent properties,Start codon: AUG (also codes methionine) Stop codon: UAA, UAG, UGA Degenerate: 2 6 codons specify one amino acid except for AUG and UGG (coding for tryptophan),Reading frame of mRNA and the importance of the start and stop codon,Reading frame: a contiguous and nonoverlapping set of three-nucleotide condons in mRNA as well as DNA. Open Reading Frame (ORF): reading frame starting with start condon and ending with stop condon.,mRNA in eukaryotes is usually monocistronic: one mRNA encodes only a single polypeptide chain.,mRNA in prokaryotes usually encodes more than one polypeptide chain. This is called polycistronic.,Polycistron and Monocisctron,It is colinear and directional: mRNA is read from 5 to 3, protein is synthesized from N terminus to C terminus.,Properties of genetic code,Colinear: amino acid sequence N to C corresponds exactly to the sequecne of their codons in the mRNA read 5 to 3.,PCR primer design: 5 to 3 for both forward and reverse primer; for protein expression, forward primer must contain start codon.,B) It is nonoverlapping and “commaless” : No overlapping (each nucleotide is used only once ) and no empty spaces in between in the coding sequence.,Properties of genetic code,Insertion or deletion leading to frameshift mutation,C) It contains 61 amino acid coding codons and 3 stop condons UAA, UAG, and UGA. Methionine coding codon AUG is also used as start condon. Application: tag and truncating mutation (insert or mutate into a stop codon),Properties of genetic code,D) It is unambiguous. Each codon specifies one and only one amino acid.,E) It is degenerate: one amino acid has more than one codon. One of the consequences of degeneracy is that a mutation which produces a base change in DNA may not result in an amino acid change in the encoded protein. Synonyms: refers to the codons for the same amino acid. e.g. GUU, GUC, GUA, GUG represent for Val.,Properties of genetic code,Degeneracy of genetic codes,F) It is universal: the genetic code system is used by all living organisms with the minor exception: in cytosol in mitochondria AUA Ile Met UGA Stop Trp AGA Arg Stop (animal) CGG