Proteins are large, complex molecules that carry out nearly all of the work within living cells. They are fundamental to the structure, function, and regulation of the body’s tissues and organs. A “protein strand” refers to the basic, linear chain of smaller units called amino acids that make up every protein. These strands are found in every cell of every living organism.
The Fundamental Components
Protein strands are constructed from smaller building blocks known as amino acids. There are 20 different types of standard amino acids, all sharing a common basic structure: a central carbon atom bonded to a hydrogen atom, an amino group, a carboxyl group, and a unique side chain. This side chain differentiates one amino acid from another, giving each its distinct chemical properties.
Amino acids link together in a specific order to form a long, unbranched chain. This connection occurs through a covalent bond known as a peptide bond. During peptide bond formation, the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water in a process called dehydration synthesis. The resulting continuous chain of amino acids forms the linear backbone of the protein strand.
How Protein Strands Fold
The linear protein strand folds into a specific three-dimensional shape. This folding is determined by the amino acid sequence, known as the protein’s primary structure. Even a slight alteration in this sequence can significantly impact the protein’s overall structure and its ability to function correctly.
As the amino acid chain elongates, localized folding patterns begin to emerge, forming what is known as the secondary structure. The most common secondary structures are the alpha-helix, a right-handed coil, and the beta-pleated sheet, which consists of parallel or antiparallel strands. These shapes are stabilized by hydrogen bonds within the protein’s backbone.
The overall three-dimensional shape of a single folded protein strand is called its tertiary structure. This complex shape arises from various interactions between the diverse side chains of the amino acids, including hydrogen bonding, ionic bonds, and other non-covalent forces. Some proteins, such as hemoglobin, are made up of multiple folded protein strands, or subunits, which assemble to form the quaternary structure. These interactions between subunits are also stabilized by various forces.
The Many Jobs of Proteins
The unique three-dimensional shapes that protein strands fold into are directly responsible for their diverse roles in the body. Proteins act as enzymes, which are biological catalysts that accelerate thousands of biochemical reactions, including the digestion of food. For example, enzymes like lipase break down dietary fats, while carbohydrase breaks down carbohydrates.
Proteins also provide structural support, forming components like collagen, which creates the connective framework for muscles, bones, and cartilage, and keratin, the main structural element in hair, nails, and skin. Other proteins function as transporters, carrying substances throughout the bloodstream and within cells. Hemoglobin, for instance, transports oxygen from the lungs to body tissues.
Beyond structure and transport, proteins serve as messengers, with some hormones acting as chemical signals that coordinate biological processes. Insulin, secreted by the pancreas, regulates blood sugar levels. Proteins also play a significant role in immune defense, with antibodies binding to foreign particles like viruses and bacteria to protect the body.