BIOLOGY 1A03 Lecture Notes - Lecture 10: Protein Structure, Metabolic Pathway, Human Genome Project
27 Jun 2018
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Charged tRNA is delivered to the functional ribosome
Translation allows for peptide bond formation
Each incoming charged tRNA is delivered in association with a GTP-bound elongation factor.
When the correct codon-anticodon pairing has been made, the GTP is then hydrolyzed and the
aminoacyl end of the tRNA is released from the elongation factor.
Termination of translation occurs at a stop codon
Once the ribosome reaches a stop codon on the mRNA sequence,
GTP-bound release factors will bind to the A-site and catalyze the
hydrolysis of the bond between the terminal amino acid in the
polypeptide and the tRNA in the P-site. Further GTP hydrolysis will also
enable the dissociation of the translation complex, including the
ribosomal subunits and any remaining bound tRNA
Overview of translation
At the start of translation in eukaryotes, initiation factors bind to the 5’
cap of the mRNA.
This recruits the small ribosomal subunit along with the methionine-
charged transfer RNA.
Once, start codon is encountered, a large subunit of the ribosome is
then able to bind to the rest of the initiation complex using the energy
released from GTP hydrolysis, and continue to scan the mRNA
molecule.
Subsequently charged tRNA molecules can then join the ribosome at the aminoacyl (or A) site,
and induce a conformational change that allows for the formation of condensation reactions as
peptide bonds, between each amino acid that is added to the growing polypeptide chain.
With each peptide bond that is formed, deacylated tRNA move from the P-site to the E site
The subsequent aminoacyl-tRNA to enter the A site will then allow for the release of the
deacylated tRNA from the E site. The process of translation is then terminated once the ribosome
reaches a stop codon on the mRNA sequence, with GTP-bound release factors now being able to
bind to the A-site and catalyzing the dissociation of the translation complex, including the
ribosomal subunits and any remaining bound tRNA.
Keep in mind – only A and P sites have a charged tRNA molecule, not E site
Unit 4 – Proteins are encoded in DNA sequences
One gene, one enzyme hypothesis (there are exceptions)
George Beadle and Edward Tatum established the relationship between genes and proteins.
This is referred to as the “one-gene-one-enzyme” hypothesis.
idea that genes act through the production of enzymes, with each gene responsible for producing
a single enzyme that in turn affects a single step in a metabolic pathway.
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