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Protein SynthesisProtein Synthesis

From: Protein Data Bank PDB ID: 1A3N

Tame, J., Vallone, B.: Deoxy Human Hemoglobin. 1998

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contentcontent IntroductionIntroduction

ProteinsProteins

Ribosome StructureRibosome Structure TransferTransfer RnaRna ((TrnaTrna))

Translation 4 Steps:Translation 4 Steps:

ActivationActivation

InitiationInitiation

ElongationElongation

TerminationTermination

Posttranslational ModificationPosttranslational Modification


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Structural and functional components ofStructural and functional components oforganisms.organisms.

Composed ofComposed ofamino acidsamino acids

order of nucleotides in DNAorder of nucleotides in DNA determinesdeterminesorder of amino acids in a proteinorder of amino acids in a protein

One geneOne gene codes for one proteincodes for one protein

PROTEINS


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TranslationTranslation

Translation:Translation:

The process of converting the information in aThe process of converting the information in a

sequence of nitrogen bases in mRNA into asequence of nitrogen bases in mRNA into asequence of amino acidssequence of amino acids

Occurs onOccurs on ribosomesribosomes

Involves a 3Involves a 3rdrd type of RNAtype of RNA

Transfer RNA (Transfer RNA (tRNAtRNA))


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Ribosome structureRibosome: an organell to covalently link amino acids based on mRNA

sequence (genetic information) using charged tRNAs

M a large complex (2500kD in bacteria) including proteins and

rRNAs (central to ribosome functions)

N number/cell: 20,000 (bacteria), 200,000 (yeast)

O bactria:70S = 30S (16S rRNA)+ 50S (23S, 5S rRNA),

eukaryotes: 80S = 60S (28S, 5.8S, 5S rRNA) + 40S (18S rRNA)

P amounts: 2/3 of mass; rRNA, 1/3; proteins (about 78 proteins in

eukaryotes)

Q Bacterial ribosome structure:

i) 30S: 16S r RNA determines structure, some flexibility (protein synthesis), 4

domains of rRNAs, 21 proteins

ii) 50S: solid, immobile, 23S and 5S rRNAs

iii) Interface between 30S and 50S: mostly rRNAs, devoid of proteins, the sitewhere mRNA and tRNA bind during protein synthesis (A, P, E sites)


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Transfer RNA (Transfer RNA (tRNAtRNA))

Function is toFunction is to bringbring amino acids toamino acids to ribosomesribosomes

to be assembled into proteinsto be assembled into proteins

Made up of about 75 nucleotidesMade up of about 75 nucleotides

EachEach tRNAtRNA moleculemolecule ONLYONLY recognizesrecognizes ONEONEamino acidamino acid


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Transfer RNA (tRNA)Transfer RNA (tRNA)

Top of tRNA moleculeTop of tRNA molecule One amino acidOne amino acid

Bottom of tRNA moleculeBottom of tRNA molecule Three nitrogen basesThree nitrogen bases

calledcalled anticodonsanticodons

AntiAnti--codonsbecause they paircodonsbecause they pairwith codonsonmRNAmoleculeswith codonsonmRNAmolecules


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Translation (protein synthesis)Translation (protein synthesis)

Information in mRNA translatedInformation in mRNA translated

into primary sequence of a proteininto primary sequen

ce of a proteinin 4 steps:in 4 steps:

ACTIVATIONACTIVATION

INITIATIONINITIATION

ELONGATIONELONGATION TERMINATIONTERMINATION


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ACTIVATIONACTIVATION

Each amino acidEach amino acidactivated byactivated byreacting with ATPreacting with ATP

tRNA synthetasetRNA synthetaseenzyme attachesenzyme attachesactivated aminoactivated aminoacid to ownacid to ownparticular tRNAparticular tRNA

Adapted from: Bettelheim FA and March J (1990) Introduction to Organic and

Biochemistry (International Edition). Philadelphia: Saunders College

Publishing p398


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INITIATIONINITIATION

mRNA attaches tomRNA attaches tosmaller body ofsmaller body ofribosomeribosome

Initiator tRNA attachesInitiator tRNA attachesto startcodonto startcodon

Larger body of ribosomeLarger body of ribosomecombines with smallercombines with smallerbodybody

From: Tortora, GJ & Grabowski SR (2000) Principles of Anatomy andPhysiology (9th Ed). New York: John Wiley & Sons. P88.


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ELONGATIONELONGATION Anticodon of next tRNA binds toAnticodon of next tRNA binds to

mRNA codon at A site ofmRNA codon at A site ofribosomeribosome Each tRNA specific for oneEach tRNA specific for one

amino acid only, but someamino acid only, but someamino acids coded for by up toamino acids coded for by up to6 codons6 codons

Order of bases in mRNAOrder of bases in mRNAcodons determine which tRNAcodons determine which tRNAanticodons will align andanticodons will align andtherefore determines order oftherefore determines order ofamino acids in proteinamino acids in protein

Amino acid at A site linked toAmino acid at A site linked toprevious amino acidprevious amino acid

Ribosome moves along oneRibosome moves along onecodon and next tRNA binds at Acodon and next tRNA binds at Asitesite From: Tortora, GJ & Grabowski SR (2000) Principles of Anatomy andPhysiology (9th Ed). New York: John Wiley & Sons. P88.


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TERMINATIONTERMINATION

Final codon on mRNAFinal codon on mRNAcontains terminationcontains termination

signalsignal

Releasing factors cleaveReleasing factors cleavepolypeptide chain frompolypeptide chain fromtRNA thatcarried finaltRNA thatcarried final

amino acidamino acid mRNA released frommRNA released from

ribosome and brokenribosome and brokendown into nucleotidesdown into nucleotides

From: Tortora, GJ & Grabowski SR (2000) Principles of Anatomy and

Physiology (9th Ed). New York: John Wiley & Sons. P88.


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Posttranslational modification

Proteolysis: a part of the maturation pathway of many proteins

M Removal of signal polypeptide

N Disulfide formation

O Glycosylation: N- & O-glycosylation

P Cleavage at specific sites

P Methyl, phosphoryl, fatty acyl groups

Q Acetylation at N-terminal

R Amidation at C-terminal

S D-configuration of amino acid


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