BIO 1140 Lecture Notes - Lecture 15: Charn, Start Codon, Exon

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BIO1140 B Dr. Caroline Petit-Turcotte
Translation (Lecture) 03.06.17
Translation: mRNA-driven protein synthesis; take matured RNA to make protein; much slower process than
transcription
ribosome attaches to RNA strand and translates its sequences into an aa chain aa is added to protein
chain as the tRNA its attached to interacts with its specific codon (3 nucleotide bases on mRNA) to make
protein
Ribosome has three distinct regions one is to read codons to recruit tRNA that have the corresponding aa
The code is degenerate (or redundant), there are synonyms but no ambiguity; there is only one aa per
codon but many codons per aa
o i.e UCU, UCC, UCA, UCG, AGU, AGC codons transport serine aa
o every eukaryotic and prokaryotic protein starts with the start codon AUG (methionine); reading
fram determined by start codon
o Reading ends with stop codons UAA, UAG, or UGA they do’t hae aa for these odos so that
riosoe kos that it’s the ed of the aa hai
Wobble Effect (oscillation) explains why there are synonyms in the codon table;
genetic code is degenerate meaning even if there are only 2 matching base pairs you
can still get the right aa
Certain aa are associated with more than one codon, the difference lies in the
3rd nucleotide; we have more codons than we need to make all 20 aas
This is how synonyms arise, it gives flexibility in reading the sequence
Exon from mRNA related to structure of proteins b/c the exons correspond to distinct
protein domains; the domains can carry out different abilities
i.e in receptor proteins they have extracellular ligand binding domain,
transmembrane domain, and intracellular domain these correspond to exons on mRNA
exons are translated in given order, all aa corresponding to exon will be associated together on mRNA;
sequence of exon determines sequence of aas translated
folding occurs later after translation
Transfer RNA (tRNA) arry the orret aa to the riosoe at their 3’
ends and recognize the mRNA sequence (codon) in their anticodon region
tRNA has a specific structure anticodon is the complementary
codon that associates with right codon on mRNA (this ensures
that the tRNA lines up correctly with mRNA); 3’ end of tRNA
carries the corresponding aa (aa never touches mRNA)
Wobble effect (oscillation) allow humans to need only 31 tRNAs
to accommodate the 61 codons
tRNA differ according to the anticodon of the tRNA
Aminoacylation: specific pairing; Aminoacyl transferases are
enzymes that allow aa to bind covalently to tRNA as long as the aa matches the codon on the
tRNA, thus there are 20 different aminoacyl transferases
o Aminoacyl transferase (enzyme) has a specific structure that recognizes only one aa
aa attaches to enzyme and ATP is loaded (2 Ps removed) to recruit tRNA by
using anticodon; due to wobble effect, only the first two codes matter (3rd
uleotide is degeerate, so its positio does’t atter) two nucleotides
determines which aa attaches to tRNA
AMP is released, now the tRNA is loaded/activated; it gets sent to ribosome to
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