Proteins are the final products of genes, which help perform the function encoded by the gene. Proteins are composed of amino acids and play important roles in the cell. All enzymes (except ribozymes) are proteins that act as catalysts to affect the rate of reactions. Proteins are also regulatory molecules, and some are hormones. Transport proteins, such as hemoglobin, help transport oxygen to various organs. Antibodies that defend against foreign particles are also proteins. In disease states, protein function may be impaired due to genetic mutations, altered gene expression, or direct damage to proteins. For instance, mutations in the hemoglobin gene lead to sickle cell anemia, where altered protein structure compromises oxygen transport (Strachan & Read, 2018).

Because proteins directly execute biological processes, the ultimate goal of proteomics is to:

• Identify which proteins are present
• Compare protein expression under normal vs diseased conditions
• Study interactions between proteins
• Predict cell behavior
• Identify potential drug targets

This protein-centered perspective provides more immediate insight into cellular activity than studying genes alone. For example, comparing proteins expressed in healthy liver cells with those in cancerous liver cells can reveal molecules involved in tumor growth and disease progression.