protein synthesis

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PROTEIN PROTEIN SYNTHESISSYNTHESIS

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3 Types of RNA• mRNA= messenger• tRNA= transfer• rRNA= ribosomal

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The Central Dogma• DNA

– The master program of the cell

– Never leaves the nucleus

• Transcription– Process that makes mRNA

from DNA– Takes place in the nucleus

• Translation– Process that makes proteins

from mRNA– Takes place in the cytoplasm

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Steps in Steps in TranscriptionTranscription

InitiationInitiation ElongationElongation TerminationTermination

When complete, When complete, pre-RNApre-RNA molecule is releasedmolecule is released

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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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RNA ProcessingRNA Processing

pre-RNA molecule

intron

intronexon exon exon

exon exon exon

Mature RNA moleculeMature RNA molecule

exon exon exon

intron intron

splicesome splicesome

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TranslationTranslation

•Synthesis of proteinsSynthesis of proteins in the in the cytoplasmcytoplasm

• Involves the following:Involves the following:

1.1. mRNA (codons)mRNA (codons)

2.2. tRNA (anticodons)tRNA (anticodons)

3.3. ribosomesribosomes

4.4. amino acidsamino acids

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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).

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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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Question:Question:

What would be the Amino What would be the Amino acid sequence for the acid sequence for the following mRNA strand?following mRNA strand?

mRNA mRNA CGAUGUUCAGACGCGGGUACGAUGUUCAGACGCGGGUA

ACGACG

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