The function of Trypsin is to break down proteins. Trypsin is a digestive enzyme that is produced in the pancreas and released into the small intestine. Its primary role is to catalyze the hydrolysis (breakdown) of peptide bonds in proteins, converting them into smaller peptides and amino acids. This process is essential for the digestion and absorption of dietary protein.

Option 1, breaking down fats, is incorrect because Trypsin specifically focuses on proteins and does not have a role in lipid digestion.

Option 2, synthesizing proteins, is incorrect because Trypsin is not involved in protein synthesis. Instead, it facilitates the breakdown of proteins.

Option 4, breaking down carbohydrates, is also incorrect because Trypsin does not have any effect on carbohydrates. Its function is limited to protein digestion.

Overall, the correct answer is option 3, which accurately describes the function of Trypsin.