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PROTEIN PROTEIN SYNTHESISSYNTHESIS
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DNA AND DNA AND GENESGENES
DNADNA
■DNA contains genes, sequences of nucleotide bases
■Genes have different alleles.
■These genes code for polypeptides (proteins)
Genes & ProteinsGenes & Proteins
Proteins are made of amino acids linked together by covalent bonds called peptide bonds
Dehydration synthesis or condensation reactions form the bonds
20 different amino acids exist
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Amino Acid StructureAmino Acid Structure
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PolypeptidesPolypeptides
■Amino acid chains are called polypeptides
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DNA Begins the DNA Begins the ProcessProcess
■DNA is found inside the nucleus
■Proteins, however, are made in the cytosol of cells by organelles called ribosomes
■Ribosomes may be free in the cytosol or attached to the surface of rough ER
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Starting with DNAStarting with DNA
■DNA ‘s codeDNA ‘s code must be must be copiedcopied and taken to the cytosoland taken to the cytosol
■In the cytosol, this In the cytosol, this code code must be readmust be read so so amino acidsamino acids can be assembled to make can be assembled to make polypeptides (proteins)polypeptides (proteins)
■This process is called This process is called PROTEIN SYNTHESISPROTEIN SYNTHESIS
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RNARNA
Roles of RNA and DNA
■DNA is the MASTER PLAN
■RNA is the copy of the Master Plan
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RNA Differs from DNARNA Differs from DNA
■ RNA has a sugar RNA has a sugar riboseribose
DNA has a sugar DNA has a sugar deoxyribosedeoxyribose
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Other DifferencesOther Differences
■ RNA contains the base RNA contains the base uracil (Uuracil (U))
DNA has DNA has thymine (T)thymine (T)
■ RNA molecule is RNA molecule is single-single-strandedstranded
DNA is DNA is double-strandeddouble-stranded
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DNA
Structure of RNAStructure of RNA
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Three Types of RNAThree Types of RNA
■Messenger RNA (mRNA)Messenger RNA (mRNA) copies copies DNA’s code & carries the genetic DNA’s code & carries the genetic information to the ribosomesinformation to the ribosomes
■Ribosomal RNA (rRNA)Ribosomal RNA (rRNA), along with , along with protein, makes up the ribosomesprotein, makes up the ribosomes
■Transfer RNA (tRNA)Transfer RNA (tRNA) transfers transfers amino acids to the ribosomes amino acids to the ribosomes where proteins are synthesizedwhere proteins are synthesized
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.
Messenger RNA
■Long Straight chain of Nucleotides
■Made in the Nucleus■Copies DNA & leaves
through nuclear pores■Contains the Nitrogen
Bases A, G, C, U ( no T )
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Messenger RNA (mRNA)Messenger RNA (mRNA)
■Carries the information for a Carries the information for a specific proteinspecific protein
■Made up of Made up of 500 to 1000 500 to 1000 nucleotides longnucleotides long
■Sequence of 3 bases called Sequence of 3 bases called codoncodon
■AUGAUG – methionine or – methionine or start codonstart codon
■UAA, UAG, or UGAUAA, UAG, or UGA – – stop codonsstop codons
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Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)
■rRNA is a single strand rRNA is a single strand 100 to 3000 nucleotides100 to 3000 nucleotides longlong
■GlobularGlobular in shape in shape■Made inside the Made inside the nucleusnucleus
of a cell in the nucleolusof a cell in the nucleolus■Associates with Associates with
proteins to form proteins to form ribosomesribosomes
■Site of Site of protein protein SynthesisSynthesis
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Transfer RNA (tRNA)Transfer RNA (tRNA)
■Clover-leaf shape■Single stranded molecule
with attachment site at one end for an amino acid
■Opposite end has three nucleotide bases called the anticodon
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Transfer RNATransfer RNA
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amino acidamino acidattachment siteattachment site
U A C
anticodonanticodon
Codons and Anticodons
■The 3 bases of an anticodon are complementary to the 3 bases of a codon
■Example: Codon ACU
Anticodon UGA
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UGA
ACU
The Genetic Code
■A codon designates an amino acid
■An amino acid may have more than one codon
■There are 20 amino acids, but 64 possible codons
■Some codons tell the ribosome to stop translating
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The Genetic Code
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•Use the code by reading from the center to the outside•Example: AUG codes for Methionine
Name the Amino Acids
■GGG?■UCA?■CAU?■GCA?■AAA?
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TRANSCRIPTION TRANSCRIPTION AND AND
TRANSLATIONTRANSLATION
Pathway to Making a Pathway to Making a ProteinProtein
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProtein
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Protein SynthesisProtein Synthesis
The production or synthesis of polypeptide chains (proteins)
Two phases: Transcription & Translation
mRNA must be processed before it leaves the nucleus of eukaryotic cells
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DNADNA RNARNA ProteinProtein
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Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryotEukaryotic Cellic Cell
TranscriptionTranscription
■The process of copying the sequence of one strand of DNA, the template strand
■mRNA copies the template strand
■Requires the enzyme RNA Polymerase
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Question:Question:
What would be the What would be the complementary RNA complementary RNA strand for the following strand for the following DNA sequence?DNA sequence?
DNA 5’-DNA 5’-GCGTATGGCGTATG-3’-3’
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Answer:Answer:
■DNA 5’-GCGTATG-DNA 5’-GCGTATG-3’3’
■RNA 3’-CGCAUAC-RNA 3’-CGCAUAC-5’5’
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TranscriptionTranscription
■During transcription, RNA polymerase binds to DNA and separates the DNA strands
■RNA Polymerase then uses one strand of DNA as a template to assemble nucleotides into RNA
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TranscriptionTranscription
■Promoters are regions on DNA that show where RNA Polymerase must bind to begin the Transcription of RNA
■Called the TATA box■Specific base sequences act as
signals to stop■Called the termination signal
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RNA PolymeraseRNA Polymerase
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mRNA ProcessingmRNA Processing
■After the DNA is transcribed into RNA, editing must be done to the nucleotide chain to make the RNA functional
■Introns, non-functional segments of DNA are snipped out of the chain
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mRNA EditingmRNA Editing■Exons, segments of RNA that
code for proteins, are then rejoined by the enzyme ligase
■A guanine triphosphate cap is added to the 5” end of the newly copied mRNA
■A poly A tail is added to the 3’ end of the RNA
■The newly processed mRNA can then leave the nucleus
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36CAP
TailNew Transcript
Result of TranscriptionResult of Transcription
mRNA Transcript
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•mRNA leaves the nucleus through its pores and goes to the ribosomes
TranslationTranslation
■Translation is the process of of decoding the mRNA into a polypeptide chain
■Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins
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TranscriptioTranscriptionn
TranslatiTranslationon
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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Step 1- InitiationStep 1- Initiation
■mRNA transcript start codon AUG attaches to the small ribosomal subunit
■Small subunit attaches to large ribosomal subunit
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mRNA transcript
RibosomesRibosomes
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PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
Step 2 - Elongation■As ribosome moves, two
tRNA with their amino acids move into site A and P of the ribosome
■Peptide bonds join the amino acids
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 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
End Product –The Protein!End Product –The Protein!
■The end products of protein synthesis is a primary structure of a protein
■A sequence of amino acid bonded together by peptide bonds
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aa1
aa2 aa3 aa4aa5
aa200
aa199
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