Aminoacyl-tRNA

Aminoacyl-tRNA is tRNA (also known as transfer ribonucleic acid) to which its cognated amino acid is adhered. Their role is to deliver the amino acid to the ribosome where it will be incorporated into the polypeptide chain that is being produced. A specific amino acid is added to each tRNA, which is crucial since it means that only that particular amino acid will be incorporated when the anticodon of that tRNA fits (can form a transient base pair with) the next codon of the mRNA that is being translated into protein.

The specific linkage of the correct amino acid to each tRNA is accomplished by aminoacyl-tRNA synthetases. Due to the degeneracy of the genetic code, some of the different tRNAs have the same amino acid attached to them.

Synthesis
Aminoacyl-tRNA (also known as charged tRNA) is produced in two steps; amino acid activation and transfer. The first step is the adenylation of the amino acid, which forms aminoacyl-AMP:

Amino acid + ATP ↔ Aminoacyl-AMP + PPi

Then, the amino acid residue is transferred to the tRNA:

Aminoacyl-AMP + tRNA ↔ Aminoacyl-tRNA + AMP

The net reaction is

Amino acid + ATP + tRNA ↔ Aminoacyl-tRNA + AMP + PPi

The net reaction is only energetically favourable because the pyrophosphate is hydrolysed; that reaction is highly energetically favourable and drives the other reactions. All of these reactions take place inside the aminoacyl-tRNA synthetase specific for that tRNA.