1 PROTEIN SYNTHESIS: Translation. 2 Transcription Translation DNA mRNA Ribosome Protein Prokaryotic...

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PROTEIN PROTEIN SYNTHESIS: SYNTHESIS: TranslationTranslation

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TranscriptionTranscription

TranslationTranslation

DNA

mRNA

Ribosome

Protein

Prokaryotic CellProkaryotic Cell

DNA DNA RNA RNA ProteinProtein

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The Genetic Code

1. is redundant- more than one codon can code for the same

amino acid

2. is continuous- reads as a series of 3-letter codons without

spaces

3. is nearly universal- almost all organisms build proteins with the same

code

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gene expression

• the transfer of genetic information from DNA to RNA to protein

TranslationTranslationmRNA is exported to the cytoplasm and

processed further by other enzymes to remove the “junk” DNA called introns

The final mRNA is transported to ribosomes where translation occurs.

Ribosomes read the mRNA in multiples of 3 nucleotides called codons

For example:5’ AUGCCCUCAGAG 3’

Codon TableCodon Table

TranslationTranslationEach codon signals the cell to retrieve

and add an amino acid to a growing chain of amino acids using transfer RNA (tRNA).

energy is used to both make the amino acids and to join them, ~200 ATP per 50 aa sequence!

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tRNA

• transfer RNA

• ssRNA, ~80 nucleotides, that has an anticodon loop and a 3’ region where an amino acid attaches

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Steps of Translation

1. Initiation• small ribosomal subunit attaches at 5’cap

and scans down

• the anticodon of tRNA attaches to the AUG start codon of mRNA, using the small ribosomal subunit as “support”

– this sets the reading frame

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• large ribosomal subunit joins – P (peptide) site: where first tRNA binds– A (amino acid) site: where next tRNA will bind– E (exit) site: where tRNA will leave from

• the ribosome is made or rRNA and proteins• made inside the cell’s nucleus

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2. Elongation

- the large ribosomal subunit catalyzes the peptide bond between the P site and the A site amino acids

- mRNA moves forward by one codon

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3. Termination

• stop codon is reached, ribosome falls off

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TranscriptioTranscriptionn

TranslatiTranslationon

AA sequence = Protein!AA sequence = Protein!Once the entire mRNA

sequence is read and translated into amino acids the chain of AA’s is released

This chain of AA’s folds and contorts into a structure called its tertiary structure*

Finally a functional protein!

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• The end….ignore the rest

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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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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

More about different types of DNA you should know about:

•Centromeric DNA (CEN) Center of chromosome, specialized sequences function with the microtubles and spindle apparatus during mitosis/meiosis.

•Telomeric DNA At extreme ends of the chromosome, maintain stability, and consist of tandem repeats. Play a role in DNA replication and stability of DNA.

•Unique-sequence DNA Often referred to as single-copy and usually code for genes.

•Repetitive-sequence DNA May be interspersed or clustered and vary in size.

SINEs short interspersed repeated sequences (100-500 bp)

LINEs long interspersed repeated sequences (>5,000 bp)

Microsatellites short tandem repeats (e.g., TTA|TTA|TTA)