Pepsin does not break down DNA. Pepsin is an enzyme that primarily breaks down proteins into smaller peptides in the stomach. DNA, on the other hand, is not affected by pepsin, as its structure is different from that of proteins. To break down DNA, specific enzymes called nucleases, such as DNase (deoxyribonuclease), are required. These enzymes target the bonds within the DNA molecule, whereas pepsin is specialized to target peptide bonds in proteins.