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