Central DogmaDNA=genotype

Transcription

RNA= the messenger

Translation

Polypeptide=phenotypephenotype

Central Dogma

DNA Transcription

RNA= the messenger TranslationTranslation

Polypeptide= phenotype

For translation to happen, the messenger RNA goes to the

cytoplasm where it is attached to a cellular

structure called a ribosome.

TranslatTranslationion : :

CODON CODON (mRNA)(mRNA)

Amino Amino AcidAcidAntiCODON AntiCODON (tRNA)(tRNA)

PolypeptiPolypeptidede

The structure of The structure of tRNAtRNA Single strand

of RNA

Folded back upon itself

Held together with H-bonds

The structure of The structure of tRNAtRNA Amino acid Amino acid

attachment attachment on 3” endon 3” end

AnticodonAnticodon couples to the couples to the mRNAmRNA

Code RedundancyCode Redundancy•Third base in a codon shows "wobble”.

•First two bases are the most important in reading the code and giving the correct amino acid. The third base often doesn’t matter.

The structure of The structure of tRNAtRNA

couplincouplingg

a.acid a.acid to the to the enzymeenzyme

EnzymeEnzyme

coupled coupled a. a.

acid acid joins joins with with

PP

EnzymeEnzyme

•PhosphaPhosphate te joins joins

to to a.a.a.a.

CouplinCouplingg

Enzyme

•PhosphaPhosphate te joins to joins to a.a. by a.a. by loosing loosing 2 P2 P

•tRNA bonds tRNA bonds to the to the amino acidamino acid

CouplinCouplingg

EnzymeEnzyme

•PhosphaPhosphate te joins to joins to a.a. a.a. (for (for energy)energy)

•tRNA bonds tRNA bonds to a.a.to a.a.

•enzyme enzyme releases releases “activated “activated amino acid”amino acid”

TWO subunits to a ribosom

e

Ribosome Ribosome Binding Binding Sites:Sites:

33

5’ cap

Large subunit attaches

• The mRNA joins to the small ribosomal unit at the 5' untranslated region. This binds to a special binding site on the small ribosomal subunit

capcap

5’ cap

Large subunit attaches

• The large ribosomal subunit attaches to the small subunit such that the first codon is aligned at the P binding site.

5’ cap

Large subunit attaches

• A tRNA carrrying the amino acid methionine attaches to the start codon (AUG) on the messenger RNA. This inititates elongation.

5’ cap

Large subunit attaches

Brings together:• mRNA• tRNA carrying the 1st amino acid

• 2 subunits of the ribosome

5’ cap

Large subunit attaches

• Attachment of first amino acid carrying tRNA to A binding site.

• A tRNA and its amino acid attaches to the A binding site.

5’ cap

Large subunit attaches

• Peptide bond formation between the met and the amino acid carried at the A bindiung site. Our polypeptide chain is now: Met -Thr

5’ cap

Large subunit attaches

• Ribosome moves in the 3' direction down the messenger RNA by three bases or one codon shifting the tRNA and polypeptide chain to the P Binding site. The A binding site is open and a vacant tRNA is in the E binding site.

5’ cap

Large subunit attaches

• tRNA ejected from the E binding site.

5’ cap

Large subunit attaches

• Repeat Elongation Step 1 - 4

• until stop codon encountered..

5’ cap

Large subunit attaches

• Elongation ends with:

• * Old tRNA ejected from the E Binding site

Elongation of Elongation of polypeptide chain:polypeptide chain:

Elongation of Elongation of polypeptide chain:polypeptide chain:

Elongation of Elongation of polypeptide chain:polypeptide chain:

Elongation of Elongation of polypeptide chain:polypeptide chain:

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Termination of Translation

Stop codon to the A site.release factor (protein) binds to

A site -- offers a water molecule (not a.a.)

5’ cap

Large subunit attaches

• The polypeptide chain is at the P site. The stop codon at the A site.

Large subunit attaches

• A Release factor protein binds to the stop codon at the A binding site.

Large subunit attaches

• Separation of translation machinary. Polypeptide chain may go to cytoplasm for further processing.

Large subunit attaches

• Release factor protein initiates separation of polypeptide chain:

• Met-Thr-His-Asp-Gly

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Termination of Translation

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Termination of Translation

mRNA is translated mRNA is translated simultaneously by simultaneously by

several ribosomes in several ribosomes in clustersclusters

NOW WHAT?????? My head is going to explode