Nucleotides don't directly build proteins. Instead, proteins are built from amino acids.

Here's how it works:

* DNA contains the genetic code for building proteins. This code is made up of sequences of nucleotides (adenine, guanine, cytosine, and thymine).

* Transcription: The DNA code is copied into a messenger molecule called mRNA (messenger RNA).

* Translation: The mRNA molecule travels to the ribosomes, where it's read three nucleotides at a time (called codons). Each codon codes for a specific amino acid.

* Amino acids are brought to the ribosome by tRNA (transfer RNA).

* The ribosome links the amino acids together in the order specified by the mRNA, creating a protein chain.

So, while nucleotides are crucial for carrying the genetic code, it's the amino acids that are the building blocks of proteins.