Question

​​​​​​1.) Describe the steps of aminoacyl-tRNA charging. What enzyme catalyzes all of these reactions?

2.) Describe how translation is regulated by phosphorylation of eIF2α.

3.) Define an operon. Why are they advantageous for bacteria?

Answer 1

The steps of aminoacyl-tRNA charging:

1. The first step is the adenylation step where the amino acid is activated using the energy from ATP, the product of the reaction is aminoacyl AMP. The pyrophosphate bi-product is simply the two end phosphate groups ( and phosphates) which the ATP loses in forming AMP.
2. tRNA charging in which adenylated amino acid (aminoacyl AMP) which remains tightly bound to the synthetase react with tRNA. This reaction results in the transfer of amino acid to the end of 3'end of tRNA via the 2' or 3' OH group of the terminal adenosine residue at the 3' end of tRNA and release of AMP.

Amino acyl tRNA synthetase is the enzyme that catalyzes all of these reactions.

How translation is regulated by phosphorylation of eIF2α.

Four distinct protein kinases are activated in response to different stress conditions. They are GCN2, PKR, HRI, and PERK. Phosphorylation of eIF2α by these kinases inhibits GDP-GTP exchange by reducing the dissociation rate of the nucleotide exchange factor eIF2B. This leads to inhibition of translation by blocking ternary complex formation. Selective translation of a subset of mRNAs continues, which allows cells to adapt to stress conditions. ER, endoplasmic reticulum. In this way, translation is regulated.

Operon: Operon can be defined as a group of two or more genes under the transcriptional control of a single promoter.

Advantage of an operon organization in a bacterium: Operon allows a bacterium to coordinately regulate a group of genes that encode proteins with a common functional goal; the expression of the structural genes occurs as a single unit.