扬州大学：《生物化学 Biochemistry》课程教学课件（讲稿）chapter22 translation（Protein Synthesis）

Translation(Protein Synthesis

Translation (Protein Synthesis)

Translation· Processing of translating the language of RNA into the language of protein·Components: mRNA transcript (which we're translating - the message or genetic code): Ribosome (machinery that makes the protein - our writing instrument)·tRNA (aminoacid carrier-ourtranslator): Amino acids (what we connect together to make the protein - the words weusetoformourtranslation)

Translation • Processing of translating the language of RNA into the language of protein. • Components • mRNA transcript (which we’re translating – the message or genetic code) • Ribosome (machinery that makes the protein – our writing instrument) • tRNA (amino acid carrier – our translator) • Amino acids (what we connect together to make the protein – the words we use to form our translation)

Information translation· Ribosomes synthesize proteins by reading the nucleotide sequence of mRNAsand polymerizing amino acids in an N→C direction.? However, there is no obvious chemical affinity between the purine andpyrimidine bases and the 20 different amino acids.· Francis Crick reasoned that adapter molecules must bridge thisinformation gap. These adapter molecules must interact specifically withboth nucleic acids (mRNAs) and amino acids

Information translation • Ribosomes synthesize proteins by reading the nucleotide sequence of mRNAs and polymerizing amino acids in an N→C direction. • However, there is no obvious chemical affinity between the purine and pyrimidine bases and the 20 different amino acids. • Francis Crick reasoned that adapter molecules must bridge this information gap. These adapter molecules must interact specifically with both nucleic acids (mRNAs) and amino acids

The Genetic CodeTABLE22-1TheStandardGeneticCodeThrdFirstPositionPesitioeSecond Positiod(s'end)(3remd): A triplet codon specifies a single amino acidUUU PheUCUUAUTyYUGUCySUOUUCPheUCCSeUACUGCTyCUUAUCA: There are 20 amino acids but 64 codonsUGAStoPUAGSIOPUUUCCCGUSCULCAUHhUACUCCGCCCCPnCACHArg: The code is degenerate (3rd base wobble)CAACGACUACCGlnProArgCcuCCGGAUUT: Code practically identical in all life formsAUCAGCtecACOAUA-ACAAGAAUGGACOAACAGG: Three stop codonsGUUGGUGHUGUCVaGCCAlaGACANDGGCGhyA0GUAValGCAAlaGluGGAGhyGAAcG(don'tspecifyaminoacids)

The Genetic Code • A triplet codon specifies a single amino acid • There are 20 amino acids but 64 codons • The code is degenerate (3rd base wobble) • Code practically identical in all life forms • Three stop codons (don’t specify amino acids)

The Genetic Code Is a Triplet Code: A group of three bases codes for one amino acid.: The code is not overlapping: The base sequence is read from a fixed starting point without punctuation: The code is degenerate, meaning that, with the exception of Met and Trp, eachamino acid can be coded by any of several triplets? Codons representing the same amino acid tend to be similar in sequence.: The genetic code is unambiguous. Each of the 61 sense" codons encodes onlyone amino acid.· The genetic code is “universal." Codon assignments are virtually the samethroughout all organisms

The Genetic Code Is a Triplet Code • A group of three bases codes for one amino acid. • The code is not overlapping. • The base sequence is read from a fixed starting point without punctuation. • The code is degenerate, meaning that, with the exception of Met and Trp, each amino acid can be coded by any of several triplets. • Codons representing the same amino acid tend to be similar in sequence. • The genetic code is unambiguous. Each of the 61 “sense” codons encodes only one amino acid. • The genetic code is “universal.” Codon assignments are virtually the same throughout all organisms

Some Codons Are biased: Because more than one codon exists for most amino acids, the possibility forvariation in codon usage arises.. Even in organisms of average base composition, codon usage may be biased·For example the Leu codons in of human genes,: CUG was used in excess of 48,000 times: CUC more than 23,000 times· UUA just 6000 times.?Preferred codons are represented by the most abundant isoacceptor tRNAs.Furthermore, mRNAs for proteins that are synthesized in abundance tend toemploy preferred codons.: Rare tRNAs correspond to rarely used codons, and messages containing suchcodons might experience delays in translation

Some Codons Are biased • Because more than one codon exists for most amino acids, the possibility for variation in codon usage arises. • Even in organisms of average base composition, codon usage may be biased. • For example the Leu codons in of human genes, • CUG was used in excess of 48,000 times • CUC more than 23,000 times • UUA just 6000 times. • Preferred codons are represented by the most abundant isoacceptor tRNAs. Furthermore, mRNAs for proteins that are synthesized in abundance tend to employ preferred codons. • Rare tRNAs correspond to rarely used codons, and messages containing such codons might experience delays in translation

TranslationThree types of RNA participate in translationmRNA: contains the genetic code to specify the amino acid sequence of theproteintRNA:carriestheaminoacidsand readsthecodeAnticodonpairswithcodonrRNA: part of the machinery (ribosome) that makes the protein productPsiteLargenbosomasubunittRNArRNA(+proteins)mRNAAOGMIMMMIOsmallribosomerRNAsubunit(+proteins)

Translation Three types of RNA participate in translation mRNA: contains the genetic code to specify the amino acid sequence of the protein tRNA: carries the amino acids and reads the code  Anticodon pairs with codon rRNA: part of the machinery (ribosome) that makes the protein product

3tRNA-OHPAcceptorstemSets of tRNAs bind individual amino acids2D structuretRNAs have specific 2D and 3D shapetRNAshave3-baseanticodonGACACTYCCUGUGloopUCGDloop Base pairs to codons in mRNAVariableloopDecodesmessageAnticodonloop*NotresponsibleAnticodonforstructuresUracil=pseudouracilD=dihydrouracil

tRNA Sets of tRNAs bind individual amino acids tRNAs have specific 2D and 3D shape tRNAs have 3-base anticodon  Base pairs to codons in mRNA  Decodes message

tRNAoSets of tRNAs bind individual amino acidsUU30-40 different tRNAs in bacterial cells?AcceptorstemUpto150inmammaliancellsIsoacceptortRNAsACACTYCCUCGloopCUGUGDloopGAG different anticodons - same amino acidVariableloop2DstructureceptorendAnticodonloopAnticodon(Otherloopsarefolded)3D structureAnticodonloop

tRNA Sets of tRNAs bind individual amino acids 30-40 different tRNAs in bacterial cells Up to 150 in mammalian cells Isoacceptor tRNAs  different anticodons – same amino acid

Charging the tRNARNAEnzymes add amino acid to tRNAAminoacyl-tRNA synthetase (AARS)aminoacidrequires energy of ATPNHAminoacyl-tRNAAMP added to amino acidAminoacidAcceptorAmino acid attached to tRNA at acceptor armcCAttachment Connected at alpha-COO- groupsitetRNAAlpha-NH, group freecorTVCloopDHU IoOPAnticodonSLLLLLLLLLLLLLLAUG

Charging the tRNA Enzymes add amino acid to tRNA  Aminoacyl-tRNA synthetase (AARS)  requires energy of ATP  AMP added to amino acid  Amino acid attached to tRNA at acceptor arm  Connected at alpha-COO- group  Alpha-NH2 group free