4.17: Role of Proteins in the Human Body
Proteins are the building block of life. They are also the most abundant macromolecules with as many diverse roles in the body. They are part of many structural components that provide unique shapes and structures to animal cells, tissues, and organs. In addition, they also act as biological catalysts and carry out several anabolic and catabolic reactions. Notably, some proteins are chemical messengers and regulate many critical processes, such as metabolism, growth, and development. They are a significant part of the body’s defense mechanism and help neutralize invading pathogens.
Role of Contractile Proteins
Actin and myosin are contractile proteins in the sarcomere— the smallest functional unit of skeletal muscles. Actin filaments interact with myosin for muscle contraction, which involves four primary phases;
I. Membrane depolarization and Ca2+ ion release,
II. Actin and myosin cross-bridge formation,
III. Sliding of actin and myosin filaments, and
IV. Sarcomere shortening.
In addition, actin and myosin are part of the cytoskeleton in body cells, facilitating cellular movements. During cell division, actin filaments and myosin work together to build a cleavage furrow that ultimately splits the cell in half, generating two daughter cells from the original.
Role of Proteins in Immunity
Immunoglobulins, also known as antibodies, are the proteins released by the immune cells in response to harmful microorganisms. These antibodies attach to the antigen of microbes and mark them for destruction by macrophages. In humans, adaptive immunity is activated by initial exposure to a pathogen, and immunological memory is created. Therefore, if the same pathogen attacks again, the immune system can mount an enhanced attack using specific antibodies against the pathogen.
Role of Protein in Membrane Transport
Some proteins, called transport proteins, are embedded in the plasma membranes and assist the transport of molecules across the membrane. They either function as a carrier or a channel facilitating the influx and efflux of molecules. For example, glucose, a hydrophilic molecule, cannot diffuse through the cells' hydrophobic lipid bilayer. Therefore, it is transported through specific membrane transport proteins called glucose transporters. There are two primary glucose transporters— facilitated diffusion glucose transporters GLUTs and sodium-glucose-linked transporters SGLTs.
