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PROTEIN PROTEIN SYNTHESISSYNTHESIS

DNA DNA and and

GeneGeness

DNADNA

•DNA contains genes, sequences of nucleotide bases

•These Genes code for 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

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Starting with DNAStarting with DNA• DNA ‘s codeDNA ‘s code must be must be copiedcopied

and taken to the cytoplasmand taken to the cytoplasm• 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

RNARNA

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Roles of RNA and DNA

•DNA is the MASTER PLAN

•RNA is the BLUEPRINT 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 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

DNA

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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 Carries the information for

a a specific proteinspecific protein• 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 – – stop stop

codonscodons

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Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)

• GlobularGlobular in in shapeshape

• Made inside the Made inside the nucleusnucleus of a cell of a cell

• Associates with Associates with proteins to form proteins to form ribosomesribosomes

• Site of Site of protein protein SynthesisSynthesis

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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

• Three 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)

• 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 RNAamino acidamino acid

attachment siteattachment site

U A C

anticodonanticodon

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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

TranscriptiTranscription and on and

TranslationTranslation

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Pathway to Making a Pathway to Making a Protein (Protein (Central Central

DogmaDogma))DNADNA

mRNAmRNA

tRNA (ribosomes)tRNA (ribosomes)

ProteinProtein

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Protein SynthesisProtein Synthesis

Two phases: Transcription & Translation

Transcription is the process the creates mRNA, tRNA, and rRna!

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TranscriptionTranscription

•The process of copying the sequence of one strand of DNA, the template strand

•mRNA copies the template strand

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TranscriptionTranscription

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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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mRNA Transcript

•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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RibosomesRibosomes

•Made of a large and small subunit

•Composed of rRNA (40%) and proteins (60%)

•Have two sites for tRNA attachment

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RibosomesRibosomes

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

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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 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

codon 2 codon 3 codon 4 codon 5 codon 6 codon 7codon 1