Pooja Seminar
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Transcript of Pooja Seminar
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Protein SynthesisProtein Synthesis
From: Protein Data Bank PDB ID: 1A3N
Tame, J., Vallone, B.: Deoxy Human Hemoglobin. 1998
By pooja
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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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Translation (protein synthesis)Translation (protein synthesis)
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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Translation (protein synthesis)Translation (protein synthesis)
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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Translation (protein synthesis)Translation (protein synthesis)
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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Translation (protein synthesis)Translation (protein synthesis)
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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