6.3 Proteins

Proteins are the most abundant biomolecules found in cells. They are defined as polymers of amino acids, which means they are made up of long chains of amino acids linked together. Proteins are essential for the structural framework of cells and play a crucial role in almost every biological process. They participate in a wide range of functions, including support, movement, enzymatic activity, transportation, and defense within an organism.

Structure of Proteins

Proteins are composed of smaller building blocks called amino acids. The number of amino acids in a protein varies depending on its type and function. For example, insulin, which regulates blood sugar levels, consists of 51 amino acids, while hemoglobin, which carries oxygen in the blood, contains 574 amino acids.

Amino Acids

Amino acids are organic molecules that join together in a specific number and sequence to form proteins. In living organisms, around 170 different types of amino acids exist, but only 20 types are commonly used in protein synthesis. These amino acids are categorized into two main groups:

• Essential Amino Acids: These are nine amino acids that the human body cannot synthesize on its own. They must be obtained from dietary sources such as meat, eggs, and dairy products.
• Non-Essential Amino Acids: These are 11 amino acids that the human body can produce internally, so they do not need to be supplied through diet.

Each amino acid consists of an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom (H), and a side chain (R group) all attached to a central carbon atom. The R group varies among amino acids and determines their chemical properties. For example, in glycine, the R group is a hydrogen atom (H), while in alanine, the R group is a methyl group (-CH₃).

Sources and Functions of Proteins

Proteins are found in a variety of food sources, which provide the necessary amino acids for protein synthesis in the body. Some of the best sources of protein include meat (such as mutton and chicken), fish, eggs, milk, pulses, and beans.

Proteins perform numerous vital functions in the human body, including:

• Structural Role: Proteins are an essential part of cell membranes and contribute to the structure of tissues. Some structural proteins, such as collagen and keratin, are the primary components of cartilage, hair, and nails.
• Enzymatic Function: Enzymes, which speed up biochemical reactions in the body, are composed of proteins. Without enzymes, essential processes such as digestion and metabolism would occur too slowly to sustain life.
• Hormonal Regulation: Some proteins function as hormones, which regulate various physiological processes. For example, insulin is a protein hormone that controls blood sugar levels.
• Oxygen Transport: Hemoglobin, a protein found in red blood cells, plays a crucial role in transporting oxygen from the lungs to different tissues in the body.
• Muscle Movement: Proteins such as actin and myosin are key components of muscle cells. They work together to facilitate muscular contractions, allowing movement and physical activity.
• Blood Clotting: Fibrin is a protein that helps in the clotting of blood. It forms a network of fibers that prevent excessive blood loss when an injury occurs.
• Immune Defense: Some proteins, known as antibodies, play a vital role in the immune system. These proteins help defend the body against harmful pathogens, such as bacteria and viruses, by identifying and neutralizing them.

Proteins are indispensable molecules in living organisms. They serve a vast range of functions, from providing structural support to facilitating chemical reactions and defending the body against infections. A balanced diet rich in protein sources ensures the proper growth, repair, and maintenance of body tissues.