Proteins are one of the four organic groups of molecules of cells, with primary, secondary, tertiary, and quaternary structures and different chemical bonds involved in each structure. Proteins account for half the dry weight of cells and perform many vital functions in living beings. Proteins are linear polypeptide chains that in their active forms are folded into unique shapes. These higher levels of protein structure are stabilized by both covalent and noncovalent interactions. Some proteins are composed of a single polypeptide chain, while others are large complexes of many polypeptide subunits. Enzymes are a class of proteins that catalyze thousands of biochemical reactions in cells. They bind specifically to substrate molecules and increase the rates of reactions by lowering the activation energy. Enzymes are regulated by cells through various activation and inhibition strategies.

At A Glance

  • Proteins are composed of amino acids folded in complex configurations called groups, and large protein molecules may contain multiple polypeptide chains.
  • Proteins play key roles in the structure, defense, transport, communication, movement, and chemical reactions in a living cell.
  • Enzymes are proteins that work as catalysts, or molecules that speed up biochemical reactions.
  • Enzymes lower the activation energy needed to begin a specific chemical reaction.
  • The shape and surface charges of an enzyme play a critical role in effecting enzymatic reactions by creating active sites where the substrate binds and the reaction occurs.
  • Cells closely regulate enzyme activity through feedback inhibition, allosteric regulation, and competitive and noncompetitive inhibition.