The Role of Protein in Building and Maintaining Muscles

Muscles are largely made of protein, and adequate protein intake is essential for keeping them strong and functional. The human body depends on three main biological molecules—carbohydrates, lipids, and proteins—along with vitamins, minerals, and water, to survive and perform daily activities. Among these, proteins play a unique and versatile role in nearly every biological process.

Proteins are built from smaller units called amino acids. These amino acids link together through covalent peptide bonds to form long chains, or polymers, that fold into biologically active structures. When we consume protein-rich foods such as meat, eggs, dairy, legumes, or nuts, our digestive system breaks them down into individual amino acids. These are then transported through the bloodstream to cells throughout the body, where they are reassembled into the specific proteins needed for growth, repair, and metabolism.

Amino acids participate in two key metabolic pathways: anabolism, the building of complex molecules, and catabolism, the breakdown of molecules for energy. Most of the proteins synthesized by the body serve as structural proteins, providing strength to muscles, connective tissues, skin, and hair. Others function as enzymes, biological catalysts that accelerate chemical reactions, making metabolism efficient and conserving energy. Some proteins act as antibodies in the immune system, while others serve as transport proteins, carrying oxygen, nutrients, and waste across cell membranes or through the bloodstream.

A newborn or growing animal requires large amounts of protein to support rapid tissue development. DNA, through its genetic code, determines the sequence of amino acids needed to build each specific protein. Remarkably, some proteins even assist in the creation of new proteins, working together with DNA and RNA—a process that highlights the self-sustaining nature of life.

To function optimally, protein must be consumed with sufficient carbohydrates, fats, vitamins, and minerals. Protein quality, influenced by digestibility and amino acid composition, determines how well a diet supports growth and health. High-quality proteins provide all essential amino acids in the right proportions, helping the body build, repair, and sustain itself efficiently throughout life.
The Role of Protein in Building and Maintaining Muscles

Myofibrils in muscle fiber

Skeletal muscles vary in shape and size. The central portion of a whole muscle is called the belly. The belly comprises smaller compartments called fascicule.

Each fasciculus consists in turn of approximately 100 to 150 individual muscle fibers that range from 1 to 40 micrometers in length and 10 micrometers in dimeter.

A muscle fiber comprises a number of long, thin, cylindrical rods known as myofibrils, the essential contractile units of muscle, which are separated from one another by a highlight specialized network of tubules the sarcoplasmic reticulum.

The sarcoplasmic reticulum, a specialized organelle that’s stores and releases calcium, is an interconnecting network of tubules running parallel with and wrapped around the myofibrils.

The major significant of the sarcoplasmic reticulum is its ability to store, release and take up calcium and thereby control muscle contraction.

Myofibrils are bathed in an aqueous fluid (sarcoplasm), which is about 75-80% water and contains mitochondria, enzymes, glycogen, adenosine triphosphate, creatine, phosphate and myoglobin.

Myofibrils range in diameter from 1 to 2 micrometers. They are grouped in clusters and run the length of the muscle fiber. In turn each myofibril comprises long, thin strands of serially linked sarcomeres. Sarcomeres are the functional unit of a muscle.
Myofibrils in muscle fiber

Glycogen – History and Property

Glycogen – History and Property
Glycogen is the only homopolysaccharides of important in human metabolism. Glycogen presence in liver was first detected in 1856 by Claude Bernard, who recognized the relationship between the glycogen of the liver and the sugar present in the blood. Subsequently other researcher proved that the common monosaccharides give rise to liver glycogen. Although the total quantity of glycogen in the human body is low, considerably less than one-tenth percent of the total body weight, its role is primarily that of a storage carbohydrate, similar to the role of starch in plants cells. It occurs predominantly in the liver where it is important in the homeostatic mechanism regulating glucose level of the blood.

Hepatocytes have the highest concentration of glycogen – up to 8% of the fresh weight in well fed state, or 100 – 120 g in an adult. In skeletal muscle, glycogen serves as a source of energy for muscle contraction. In the muscles, glycogen is found in a much lower concentration (1% of the muscle mass), but the total amount exceeds that in liver.

Glycogen is a branched chain polymer of 6,000 to 30,000 glucose units. It is similar to amylopectin in structure but is more highly branched. The average chain length is only 10 to 24 glucose units with 3 to 4 glucose units between branching points. The size of the molecules varies with its source and with the metabolic state of the body. Muscle glycogen is estimated to have a molecular weight of about 1000000 where as the liver of glycogen molecule is much larger, approximately 5 X 1000000. Both molecules, however, constantly change in size as glucose molecules are added or removed.

Glycogen plays an important role in the glucose cycle. The most common disease in which glycogen metabolism becomes abnormal is diabetes, in which, because of abnormal amounts of insulin, liver glycogen can be abnormally accumulated or depleted.
Glycogen – History and Property