生化2014 c17 protein translation.ppt
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1、Biochemistry,Dept. of Biochemistry and Molecular Biology,Professor Wu Yaosheng 2014-06,Chapter 17,Protein Biosynthesis,Protein Biosynthesis,Genes,Gene expression,?,A G C T,A G C U,20种 AA,4,Questions,1.What are requirements for one protein biosythesis in eukaryote cells?,4. Studies have shown that th
2、e occurrence of a disease associated with abnormal changes of the structure of a protein in hepatocytes. I ask, how to identify this protein structure has changed? Whether to put forward your ideas?,3.How to synthesize a molecule of hemoglobin with biological functions by gene expression process?,2.
3、 How many sequences of DNA could code for the fragment of one peptide Glu-Glu-Met-Trp-Asp?,5,Section 1 Protein Biosynthesis System,Major Topics,Section 2 Linkage of Amino Acids with tRNA,Section 4 Modification and Target Transportation of Post-translation,Section 5 Interference and Inhibition of Pro
4、tein Biosynthesis,Section 3 Biosynthesis Process of Polypeptide chain,6,Key Points,Functions of mRNA, tRNA, rRNA during Pr synthesis, genetic codon characters Action characters of aminoacyl-tRNA synthetase Comparison of the translation process in prokaryote and in eukaryote Molecular chaperone and m
5、odification types post-translation Signal peptides and their actions, directional transportation characteristics Mechanism of translation inhibition by antiboitics, toxins, and interferons,7,Biological Synthesis Process of Protein,The activation and transfer of amino acids,The synthesis of polypepti
6、de,The modification of post-translation,Initiation,Elongation,Termination,Entry of aminoacyl-tRNA,Formation of peptide bond,Translocation of ribosome,Ribosomal cycle,8,Section One,Protein Biosynthesis System,Distinguish monocistron and polycistron; Wobble, Degeneracy of codons,Key points,Functions o
7、f mRNA, tRNA, ribosome; ORF, codons and their characters,Difficulties,10,Requirements of Protein Biosynthesis,Various RNAs: mRNA、 rRNA 、tRNA,Substrate: amino acids,Protein factors: Initiation factors,Elongation factors,Termination factors,Enzyme: aminoacyl-tRNA synthetase peptidyltransferase,Energy
8、supply: ATP, GTP,Inorganic ion: Mg2+,11,1. Messenger RNA (mRNA) and Its Codes,Messenger RNA is a polycistron in prokaryotes, but a monocistron in eukaryotes,Proteins,Protein,Function: As a template of protein synthesis,Cistron: encode one polypeptide,12,Concept of codons,The genetic code is the set
9、of rules that specify how the nucleotide sequence of an mRNA is translated into the amino acid sequence of a polypeptide.,Each amino acid in a protein is represented by three consecutive bases in mRNA, and these three-base combination, or triplets, are called codons .,13,The genetic code consists of
10、 64 triplet codons (A, G, C, U) , 43 = 64,Termination (stop) codons:,Start codon:,UAA, UAG, UGA,AUG (methionine),14,The Genetic Code,UUU UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA AUG GUU GUC GUA GUG,UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG GCU GCC GCA GCG,UAU UAC UAA UAG CAU CAC CAA CAG AAU AAC
11、 AAA AAG GAU GAC GAA GAG,UGU UGC UGA UGG CGU CGC CGA CGG AGU AGC AGA AGG GGU GGC GGA GGG,Phenylalanine Leucine Leucine Valine,Isoleucine Methionine,Serine Proline Threonine Alanine,Tyrosine Stop Histidine Glutamine Asparagine Lysine Aspartic acid Glutamic acid,Cysteine Arginine Serine Arginine Glyci
12、ne,Stop Tryptophan,15,Characteristics of codons on mRNA,(1) Direction (方向性),(2) Commaless (连续性),(3) Degeneracy (简并性),(5) Wobble (摆动性),(4) Universality (通用性),16,Reading frame Reading frame is determined by the AUG initiation codon. Every subsequent triplet is read as a codon until reaching a stop cod
13、on.,Met Ala Glu Trp Leu Ser Met Ser stop,17,18,Hemoglobin Wayne (3 terminal frameshift mutation),Normal -globin ACG UCU AAA UAC CGU UAA GCU GGA GCC UCG GUA. Thr Ser Lys Tyr Arg stop,mutated region,Wayne -globin .ACG UCA AAU ACC GUU AAG CUG GAG CCU CGG UAG Thr Ser Asn Thr Val Lys Leu Glu Pro Arg stop
14、,19,Degeneracy,Most amino acids have more than one codon, means degenerate. Codons that specify the same amino acid often differ only in the third base.,A mutation only with a base change in DNA may not result in amino acid change in the encoded protein.,CUA CUG ( Leu Leu ) without affecting transla
15、tion,20,Degeneracy(简并性),Amino acid No. of codon Amino acid No. of codon,21,Universality,The genetic code is the same in most organisms.,Exceptions are found in mitochondrial genome, where some codons specify different amino acids to those normally encoded by nuclear genes.,In some mitochondria, the
16、UGA codon no longer specifies termination of translation but instead encodes tryptophan.,22,23,Preference,Leucine codons(89) of ribosome protein in E.coli Total 1209 codons UUA UUG CUU CUC CUA CUG 1 2 4 3 0 79,23,Wobble,The first base on the anticodon always pairs with the third base on the codon an
17、d not strictly obeys the rules of base-pairing.,Codon-anticodon base-pairing is antiparallel.,Codon-anticodon interactions,One tRNA can interact with more than one codon (therefore 50 tRNAs).,The third position in the codon is frequently degenerate.,24,25,U,摆动配对,Wobble pairing of anticodon with codo
18、n,26,one tRNAleu can read two of the leucine codons,27,tRNA is the “adaptor” molecule in protein synthesis.,2.Transfer RNA (tRNA),Two functional sites: (1) acceptor stem CCA-OH 3 terminus can carry amino acid on terminal adenosine. (2) anticodon stem and anticodon loop To recognize the codon on mRNA
19、,28,(1) acceptor stem,(2) anticodon stem and anticodon loop,The secondary structure of tRNA,29,DHU arm,Anticodon,Acceptor arm,arm,30,tRNA,31,prokaryotic ribosome,eukaryotic ribosome,3. rRNAs and Ribosomes,32,Ribosomes was organized in three ways,Polysomes several ribosomes bind to and translate a si
20、ngle mRNA simultaneously Free ribosomes Synthesize proteins of cytosol, nucleus, mitochondria Membrane bound ribosomes Synthesize secreted proteins or membrane protein,33,polypeptide chain,amino acids,Large subunit,The functions of ribosome: For the assembly of amino acids to be a polypeptide chain,
21、34,Questions,1. Degenerate codons differ mostly in,A. the identities of their first base. B. the identities of their second base. C. the identities of their third base. D. the wobble position. E. Choices three and four are both correct.,35,35,Questions,2. Ribosomes select the correct tRNAs,A. and th
22、en charge them using the appropriate synthetase. B. then bind to the appropriate mRNA. C. solely on the basis of their anticodons. D. with the least abundant anticodons. E. depending on their abundance in the cytosol.,36,Questions,3. Degenerate of genetic codon means that,A.1 AA has more than 2 codo
23、ns B.2 codons could be combined as 1 codon C.each amino acid always has several codons D.1 codon can represent different amino acid. E.1 amino acid only has 1 codon.,37,Questions,4. The anticodon Which can pair to the codon CGA on mRNA is,A、GCU B、UCG C、CCA D、UCU E、ACU,38,Section Two,Linkage of Amino
24、 Acid with tRNA,The activation and transfer of amino acids,Aminoacyl-tRNA synthetase,Two specificities, To catalyze the formation of ester bond between tRNA and amino acid To proofread the wrong ester bond,Two activities, To recognize the amino acid To recognize the tRNA,40,Amino acid + ATP,Aminoacy
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