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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 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 before processed before
it leaves the nucleusit leaves the nucleus of of eukaryotic cellseukaryotic cells
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TranscriptionTranscription
TranslationTranslation
DNA
mRNA
Ribosome
Protein
Prokaryotic CellProkaryotic Cell
DNA DNA RNA RNA ProteinProtein
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DNA DNA RNA RNA ProteinProtein
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryotEukaryotic Cellic Cell
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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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.
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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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 called Amino acids chains are 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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Overview of Overview of TranscriptionTranscription
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 RNA joins the RNA nucleotides so that the nucleotides so that the codons codons in mRNA are complementaryin mRNA are complementary to to the triplet code in DNAthe triplet code 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 is molecule is
releasedreleased
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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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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)
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
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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
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Transfer RNA (tRNA)Transfer RNA (tRNA)
amino acidamino acidattachment siteattachment site
U A C
anticodonanticodon
methionine amino acidamino acid
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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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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).
Let’s Make a Protein !Let’s Make a Protein !
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mRNA Codons Join the mRNA Codons Join the RibosomeRibosome
PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
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InitiationInitiation
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 U G C U A C U U C G
1-tRNA
2-tRNA
U A C
G
aa1
aa2
A UA
peptide bond
3-tRNA
G A A
aa3
Ribosomes move over one codon
(leaves)
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1
aa2
A UA
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
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mRNAmRNA
A U G C U A C U U C G
2-tRNA
G
aa1aa2
A U
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
(leaves)
Ribosomes move over one codon
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mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
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mRNAmRNA
G C U A C U U C G
aa1aa2
A
peptide bonds
3-tRNA
G A A
aa3
4-tRNA
G C U
aa4
A C U
U G A
5-tRNA
aa5
Ribosomes move over one codon
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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
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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
aa1
aa2 aa3 aa4aa5
aa200
aa199
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