What part of DNA directs a cell to make a certain protein

A gene is the part of DNA that produces the certain proteins.

A gene

Explanation: A gene is the part of DNA that encodes information needed to produce a functional biological product or a protein. DNAs are made up of:

1). segments that do not code for any biological functional product or protein. These DNA segments are called introns or intervening sequences.

2). Segments that code for an RNA or a protein. A gene is a segment of a DNA that codes for a protein or an RNA. These segments are called exons.