BIOLOGY 1A03 Lecture Notes - Lecture 9: Methionine, Messenger Rna, Aminoacyl Trna Synthetase
27 Jun 2018
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Theme 2 – From Gene to Protein : Module 3 – Translation
Unit 1 – Molecular components contribute to translation
Translation requires many components
tRNA Structure allows for specificity in translation
tRNA molecules are able to transfer amino acids, from a pool of cytoplasmically situated amino
acids, to a growing polypeptide strand in a ribosome.
Each tRNA molecule isn’t identical & translate a specific mRNA codon into a specific amino acid.
Each tRNA molecule is made up of a single RNA strand - 70-90 nucleotides in length
An anticodon region of the tRNA molecule is a specific nucleotide triplet that forms complementary
base-pairs with a specific mRNA codon that codes for a specific amino acid.
These anticodons are conventionally written in the 3’5’ direction and align properly with mRNA
codons in the 5’3’ direction. At the 3’ end of the tRNA molecule, there is a protruding amino acid
attachment site that is made up of a single stranded CCA nucleotide sequence. The terminal A (or
adenine) is the actual point of attachment for an amino acid during an important process referred
to as tRNA molecule activation.
Aminoacyl tRNA synthetase activates tRNA molecules
Each aminoacyl tRNA synthetase is specific to the type of tRNA and corresponding amino acid
that it will bind. In particular, the active site of these enzymes recognizes the anticodon end of the
tRNA and the region of the amino acid attachment site.
There are 20 aminoacyl tRNA synthetases, one for each amino acid.
Once bound to the active site, these enzymes can then catalyze the covalent attachment of a
tRNA molecule to its amino acid using the energy from ATP hydrolysis. This leads to a charged
tRNA molecule, or an aminoacyl tRNA being released from the enzyme, which can now deliver its
specific amino acid to a growing polypeptide chain on a ribosome.
Translation involves codon-anticodon pairing
There are approximately 45 tRNA molecules meaning that some tRNA
molecules may be able to bind to more than one codon.
This is largely due to the chemical nature of the codon-anticodon pairing
interactions.
While the first base (or 5’ end) of the codon will bind with the last base (or 3’
end of the anticodon), there is a greater flexibility for base pairing between the
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Document Summary
Theme 2 from gene to protein : module 3 translation. At the 3" end of the trna molecule, there is a protruding amino acid attachment site that is made up of a single stranded cca nucleotide sequence. This flexibility is often referred to as wobble and is what also helps explain the redundancy of the genetic code. Unit 2 translation occurs in the cytosol of the cell (cid:57) ribosomes assemble along mrna (cid:120) (cid:120) In prokaryotes, this assembly and translation occurs in the cytoplasm immediately after the mrna is transcribed from the dna template. In eukaryotes, transcription and translation are two separate processes, often due the compartmentalization of dna into the nucleus and ribosomes in the cytoplasm. Unit 3 the process of translation (cid:57) translation initiation (cid:120) The mrna can therefore be a polycistronic mrna that codes for several polypeptides (cid:57) assembling an initiation complex (cid:120)
