1 protein synthesis copyright cmassengale. i.dna and genes 2copyright cmassengale
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PROTEIN PROTEIN SYNTHESISSYNTHESIS
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I.DNA I.DNA and and
GeneGeness
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DNADNA
•DNA contains genes, sequences of nucleotide bases
•These Genes code for polypeptides (proteins)
•Proteins are used to build cells and do much of the work inside cells
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Genes & ProteinsGenes & Proteins
Proteins are made of amino acids linked together by peptide bonds
20 different amino acids exist
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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 cytoplasm of cells by organelles called ribosomes
• Ribosomes may be free in the cytoplasm 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
by the mRNA (transcription)by the mRNA (transcription)• In the cytoplasm, this In the cytoplasm, 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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II.II.RNARNA
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Roles of RNA and DNA
•DNA is the MASTER PLAN
•RNA is the BLUEPRINT of the
Master Plancopyright cmassengale
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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 RNA contains the base the base uracil uracil (U(U))DNA has DNA has thymine (T)thymine (T)
• RNA molecule is RNA molecule is single-strandedsingle-strandedDNA is DNA is double-double-strandedstranded
DNAcopyright cmassengale
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Structure of RNAStructure of RNA
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. Three Types of Three Types of RNARNA
• Messenger RNA (mRNA)Messenger RNA (mRNA) copies DNA’s code & carries copies DNA’s code & carries the genetic information to the the genetic information to the ribosomesribosomes
• Ribosomal RNA (rRNA)Ribosomal RNA (rRNA), along , along with protein, makes up the with protein, makes up the ribosomesribosomes
• Transfer RNA (tRNA)Transfer RNA (tRNA) transfers transfers amino acids to the ribosomes amino acids to the ribosomes where proteins are where proteins are synthesizedsynthesized
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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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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
•Use the code by reading from the center to the outside•Example: AUG codes for Methionine
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Name the Amino Acids
•GGG?•UCA?•CAU?•GCA?•AAA?
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Remember the Remember the Complementary Complementary
BasesBasesOn DNA: A-T C-GOn RNA: A-U C-G
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Transfer RNA Transfer RNA (tRNA)(tRNA)
• 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 RNAamino acidamino acid
attachment siteattachment site
U A C
anticodonanticodoncopyright cmassengale
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Codons and Anticodons
• The 3 bases of an anticodon are complementary to the 3 bases of a codon
• Example: Codon ACU
Anticodon UGA
UGA
ACU
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III.III.TranscriptiTranscripti
on and on and TranslationTranslation
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Pathway to Making a Pathway to Making a ProteinProtein
DNADNA
mRNAmRNA
tRNA (ribosomes)tRNA (ribosomes)
ProteinProteincopyright cmassengale
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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
Nuclearmembrane
TranscriptionTranscription
RNA ProcessingRNA Processing
TranslationTranslation
DNA
Pre-mRNA
mRNA
Ribosome
Protein
EukaryotEukaryotic Cellic Cell
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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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Template Strand
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Question:Question: What would be the What would be the
complementary mRNA complementary mRNA strand for the following strand for the following DNA sequence?DNA sequence?
DNA DNA GCGTATGGCGTATG
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Answer:Answer:
•DNA GCGTATGDNA GCGTATG•mRNA CGCAUACmRNA CGCAUAC
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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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RNA PolymeraseRNA Polymerase
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mRNA Transcription
•mRNA leaves the nucleus through its pores and goes to the ribosomes
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TranslationTranslation
•Translation is the process 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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TranslationTranslation•Translation is the
process of __________________
• _______ read mRNA three bases or ______ at a time and construct the proteins
•A chain of polypeptides is a _______ (w/a _____ & _____ code).copyright cmassengale
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TranscriptioTranscriptionn
TranslatiTranslationon
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RibosomesRibosomes
PSite
ASite
Largesubunit
Small subunit
mRNAmRNA
A U G C U A C U U C G
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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 codoncopyright cmassengale
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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 codoncopyright cmassengale
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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 synthesis is a primary structure of a protein
• A sequence of amino acid bonded together by peptide bonds
aa1
aa2 aa3 aa4aa5
aa200
aa199
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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
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1
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