1 PROTEIN SYNTHESIS copyright cmassengale. I.DNA and Genes 2copyright cmassengale

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PROTEIN PROTEIN SYNTHESISSYNTHESIS

copyright cmassengale

I.DNA I.DNA and and

GeneGeness

2copyright cmassengale

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


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


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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• 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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• 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


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


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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1 PROTEIN SYNTHESIS copyright cmassengale. I.DNA and Genes 2copyright cmassengale