4.3 - Proteins

Protein is present in all living organisms. It is a highly complex substance that contains carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus elements. Protein is formed by combining one or more polypeptides. Here are some of the few terms related to proteins:

Figure 10 - Food such as meat, fish, eggs and dairy products are important protein sources.

• Polypeptide - made up of at least 50 amino acids joined together via peptide bonds.
• Dipeptides - only consist of 2 amino acids joined together.
• Amino acid – basic unit that make up proteins

Figure 11 - Amino acids (left) are the smallest units that make up a protein. There are 20 different amino acids. Dipeptide (middle) is 2 amino acids joined together via peptide bond. Tripeptide (right) is 3 amino acids combined together via peptide bonds.

The process of combining amino acids together is also called condensation. Water molecule is produced during the condensation. Protein hydrolysis refers to the breaking down of protein into its constituent amino acids. Water is needed in this process for hydrolysis to work.

Figure 12 - Many amino acids join together to form a long-chain polypeptide. The polypeptide then folds itself into specific protein structures. The shape that the proteins take on depends on the interactions between the side chains of the amino acids

Importance of Proteins in a Cell

• Build new cells
• Repair damaged tissues
• Synthesize enzymes, antibodies, hemoglobin
• Form keratin (hair), collagen (bone), myosin (muscle)
• Maintain pH fluid balance