Final answer:
Proteins are essential organic compounds made up primarily of amino acids, with diverse functions and structures in living organisms. They are categorized as either fibrous and insoluble or globular and soluble and provide energy density comparable to carbohydrates.
Step-by-step explanation:
Characteristics of Proteins
Proteins are organic compounds essential to the structure and function of all living cells. They are composed of amino acids and have a wide variety of roles within organisms. Proteins can be classified into two categories: (1) fiberlike and insoluble, such as keratins, collagens, myosins, and elastins, which serve structural, connective, and protective functions; and (2) globular and soluble, which often function as enzymes, antibodies, and messengers.
Proteins are also responsible for muscle contraction, forming blood clots, and supporting the immune system. Their ability to bind specifically and tightly with other molecules is a key characteristic that allows proteins to carry out their diverse functions.
The molar mass of proteins ranges from several thousand to several million daltons, and their composition includes not only carbon, hydrogen, and oxygen, but also nitrogen and sulfur, and in some cases phosphorus and other elements. Each protein has a unique sequence of amino acids, defining its specific structure and function. As a fuel source, proteins provide as much energy density as carbohydrates: 4 kcal (17 kJ) per gram.