The molecule that carries an amino acid from the cytoplasm to a ribosome is called transfer RNA (tRNA).

Here's how it works:

* Amino acid attachment: Each tRNA molecule has a specific three-nucleotide sequence called an anticodon that is complementary to a codon on mRNA. The tRNA also has an attachment site where a specific amino acid can bind.

* Recognition of the mRNA codon: During protein synthesis, the tRNA with the correct anticodon binds to the mRNA codon at the ribosome.

* Amino acid delivery: The tRNA delivers the attached amino acid to the ribosome, where it is added to the growing polypeptide chain.

Think of tRNA as a delivery truck, carrying the correct amino acid to the ribosome based on the instructions encoded in the mRNA.