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PROTEIN SYNTHESIS. Protein Synthesis. The production (synthesis) of polypeptide chains (proteins) Two phases: Transcription & Translation mRNA must be processed before it leaves the nucleus of eukaryotic cells. DNA. Transcription. mRNA. Ribosome. Translation. Protein. - PowerPoint PPT Presentation
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PROTEIN PROTEIN SYNTHESISSYNTHESIS
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Protein SynthesisProtein Synthesis The production (synthesis) of The production (synthesis) of
polypeptide chains polypeptide chains (proteins)(proteins) Two phases:Two phases:
Transcription Transcription & & TranslationTranslation mRNA must be mRNA must be processed processed
before it leaves the nucleusbefore it leaves the nucleus of of eukaryotic cellseukaryotic cells
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DNA DNA RNA RNA ProteinProtein
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TranscriptionTranscription
TranslationTranslation
DNA
mRNA
Ribosome
Protein
Prokaryotic CellProkaryotic Cell
DNA DNA RNA RNA ProteinProtein
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Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryotEukaryotic Cellic Cell
Pathway to Making a Pathway to Making a ProteinProtein
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProtein5
DNA or Protein?DNA or Protein? Walter Sutton discovered Walter Sutton discovered
chromosomes chromosomes were made were made of of DNA and ProteinDNA and Protein
However, scientists were However, scientists were NOTNOT sure which one sure which one (protein or DNA) was (protein or DNA) was the the actual genetic material actual genetic material of the cellof the cell
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DNA!DNA! Frederick GriffithFrederick Griffith in in
1928 showed the 1928 showed the DNADNA was the cell’s was the cell’s genetic materialgenetic material
Watson & CrickWatson & Crick in in the 1950’s built the the 1950’s built the 11stst model of DNA model of DNA
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Steps in DNA Steps in DNA ReplicationReplication
Occurs when Occurs when chromosomes chromosomes duplicateduplicate (make copies) (make copies) An An exact copyexact copy of the DNA is of the DNA is produced with the aid of the produced with the aid of the enzyme enzyme DNA polymeraseDNA polymerase Hydrogen bondsHydrogen bonds between bases between bases breakbreak and enzymes “unzip” the and enzymes “unzip” the moleculemolecule Each Each old strandold strand of nucleotides of nucleotides serves as a serves as a templatetemplate for each new for each new strandstrand New nucleotidesNew nucleotides move into move into complementary positions are joined complementary positions are joined by DNA polymeraseby DNA polymerase
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Two New, Two New, Identical Identical
DNA DNA Strands Strands Result Result from from
ReplicatioReplicatio
nn
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RNA Differs from DNARNA Differs from DNA1.1. RNARNA has a sugar has a sugar riboseribose
DNADNA has a sugar has a sugar deoxyribosedeoxyribose
2.2. RNARNA contains the base contains the base uracil uracil (U)(U)
DNADNA has has thymine (T)thymine (T)
3.3. RNARNA molecule is molecule is single-single-strandedstranded
DNADNA is is double-strandeddouble-stranded
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Structure of RNAStructure of RNA
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Three Types of RNAThree Types of RNA
• Messenger RNA (mRNA)Messenger RNA (mRNA) carries genetic information carries genetic information to the ribosomesto the ribosomes
• Ribosomal RNA (rRNA)Ribosomal RNA (rRNA), , along with protein, makes along with protein, makes up the up the ribosomesribosomes
• Transfer RNA (tRNA)Transfer RNA (tRNA) transfers amino acids to the transfers amino acids to the ribosomes where proteins ribosomes where proteins are synthesizedare synthesized
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.
Making a Making a ProteinProtein
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Genes & ProteinsGenes & Proteins ProteinsProteins are made of are made of amino amino
acidsacids linked together by linked together by peptide bondspeptide bonds
2020 different amino acids different amino acids existexist
Amino acids chains are Amino acids chains are called called polypeptidespolypeptides
Segment of DNA that codes Segment of DNA that codes for the amino acid sequence for the amino acid sequence in a protein are called in a protein are called genesgenes
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Two Parts of Protein Two Parts of Protein SynthesisSynthesis
TranscriptionTranscription makes an RNA makes an RNA molecule complementary to molecule complementary to a portion of DNAa portion of DNA
TranslationTranslation occurs when the occurs when the sequence of bases of mRNA sequence of bases of mRNA DIRECTSDIRECTS the the sequence of sequence of amino acidsamino acids in a polypeptide in a polypeptide
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Genetic CodeGenetic Code DNA contains a DNA contains a triplet codetriplet code Every three bases on DNA Every three bases on DNA
stands for stands for ONE amino acidONE amino acid Each three-letter unit on Each three-letter unit on mRNAmRNA
is called a is called a codoncodon Most amino acids have more Most amino acids have more
than one codon!than one codon! There are There are 20 amino acids20 amino acids with with
a possible 64 different tripletsa possible 64 different triplets The code is nearly The code is nearly universal universal
among living organismsamong living organisms
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TranscriptioTranscriptionn
TranslatiTranslationon
Overview of TranscriptionOverview of Transcription During During transcriptiontranscription in the in the
nucleus, a segment of DNA nucleus, a segment of DNA unwinds and unzips, and the unwinds and unzips, and the DNA DNA serves as aserves as a template for template for mRNA formationmRNA formation
RNA polymeraseRNA polymerase joins the joins the RNA nucleotides so that the RNA nucleotides so that the codons in mRNA are codons in mRNA are complementarycomplementary to the triplet to the triplet code in DNAcode in DNA
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Steps in Steps in TranscriptionTranscription The transfer of information in the The transfer of information in the
nucleusnucleus from a from a DNADNA molecule to an molecule to an RNARNA molecule molecule
Only 1 Only 1 DNADNA strand serves as the strand serves as the templatetemplate
Starts at promoter Starts at promoter DNADNA (TATA box) (TATA box) Ends at terminator Ends at terminator DNADNA (stop) (stop) When complete, When complete, pre-RNApre-RNA molecule molecule
is releasedis released
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TranscriptionTranscription
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What is the What is the enzymeenzyme
responsible for responsible for the production of the production of
the mRNA the mRNA molecule?molecule?
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RNA PolymeraseRNA Polymerase
EnzymeEnzyme found in the found in the nucleusnucleus
Separates Separates the two DNA the two DNA strands by strands by breaking the breaking the hydrogen bondshydrogen bonds between between the basesthe bases
Then moves along one of Then moves along one of the DNA strands and the DNA strands and links links RNA nucleotidesRNA nucleotides together together
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DNADNA
pre-mRNApre-mRNA
RNA PolymeraseRNA Polymerase
Processing Pre-mRNAProcessing Pre-mRNA
• Also occurs in the Also occurs in the nucleusnucleus• Pre-mRNA Pre-mRNA made up of segments made up of segments
called called introns & exonsintrons & exons• Exons code for proteins, while Exons code for proteins, while
introns do NOT!introns do NOT!• Introns spliced out by Introns spliced out by splicesome-splicesome-
enzymeenzyme and exons re-join and exons re-join
• End product is a End product is a mature RNAmature RNA molecule that leaves the nucleus molecule that leaves the nucleus to the cytoplasmto the cytoplasm
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RNA ProcessingRNA Processing
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pre-RNA molecule
intron
intronexon exon exon
exon exon exon
Mature RNA moleculeMature RNA molecule
exon exon exon
intron intron
splicesome splicesome
Messenger RNA Messenger RNA (mRNA)(mRNA)
• Carries the information for a Carries the information for a specific proteinspecific protein
• Made up of Made up of 500 to 1000500 to 1000 nucleotides longnucleotides long
• Sequence of 3 bases called Sequence of 3 bases called codoncodon
• AUGAUG – methionine or – methionine or start start codoncodon• UAA, UAG, or UGAUAA, UAG, or UGA – – stopstop codons codons
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Messenger RNA Messenger RNA (mRNA)(mRNA)
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methionine glycine serine isoleucine glycine alanine stopcodon
proteinprotein
A U G G G C U C C A U C G G C G C A U A AmRNAmRNA
startcodon
Primary structure of a proteinPrimary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
Transfer RNA (tRNA)Transfer RNA (tRNA)• Made up of Made up of 75 to 80 nucleotides75 to 80 nucleotides
longlong• Picks up the appropriate Picks up the appropriate amino amino
acidacid floating in the cytoplasm floating in the cytoplasm • Transports Transports amino acidsamino acids to the to the
mRNAmRNA• Have Have anticodonsanticodons that are that are
complementary to complementary to mRNA codonsmRNA codons• Recognizes the appropriate Recognizes the appropriate codonscodons
on the on the mRNAmRNA and bonds to them and bonds to them with H-bondswith H-bonds 30
Transfer RNA (tRNA)Transfer RNA (tRNA)
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amino acidamino acidattachment siteattachment site
U A C
anticodonanticodon
methionine amino acidamino acid
Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)• Made up of Made up of
rRNA is rRNA is 100 to 100 to 3000 3000 nucleotidesnucleotides long long
• Made inside the Made inside the nucleusnucleus of a cell of a cell
• Associates with Associates with proteins to form proteins to form ribosomesribosomes
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RibosomesRibosomes
• Made of a large and small subunit
• Composed of rRNA (40%) and proteins (60%)
• Have two sites for tRNA attachment --- P and A
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RibosomesRibosomes
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PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
TranslationTranslation
• Synthesis of proteinsSynthesis of proteins in the in the cytoplasmcytoplasm
• Involves the following:Involves the following:1.1. mRNA (codons)mRNA (codons)2.2. tRNA (anticodons)tRNA (anticodons)3.3. ribosomesribosomes4.4. amino acidsamino acids
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TranslationTranslation
• Three steps:Three steps:
1.1. initiationinitiation: start codon (AUG): start codon (AUG)
2.2. elongationelongation: amino acids : amino acids linkedlinked
3.3. terminationtermination: stop codon : stop codon (UAG, UAA, or UGA).(UAG, UAA, or UGA).
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Let’s Make a Protein !Let’s Make a Protein !
mRNA Codons Join the mRNA Codons Join the RibosomeRibosome
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PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
InitiationInitiation
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa2
A U
A
1-tRNA
U A C
aa1
anticodon
hydrogenbonds codon
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mRNAmRNA
A U G C U A C U U C G
1-tRNA 2-tRNA
U A C G
aa1 aa2
A UA
anticodon
hydrogenbonds codon
peptide bond
3-tRNA
G A A
aa3
ElongationElongation
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mRNAmRNA
A C A U G U
aa1
aa2
U
primaryprimarystructurestructureof a proteinof a protein
aa3
200-tRNA
aa4
U A G
aa5
C U
aa200
aa199
terminatorterminator or stopor stop codoncodon
TerminationTermination
End Product –The End Product –The Protein!Protein!
• The end products of protein The end products of protein synthesis is a synthesis is a primary structureprimary structure of a proteinof a protein
• A A sequence of amino acidsequence of amino acid bonded together by peptide bonded together by peptide bondsbonds
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aa1
aa2 aa3 aa4aa5
aa200
aa199