Proteins are an extremely important macromolecule with a variety of functions. Twenty different amino acids are the monomers which make up proteins.
One of the most important functions of proteins is as enzymes. Enzymes catalyze reactions by lowering the energy barrier. The energy barrier is also called the energy of activation (the amount of energy the reactants must absorb to carry out the reaction). If we did not have enzymes to aid our chemical reactions, the reactions would surely happen to slowly to sustain our life. Most enzymes are substrate specific- meaning that their active space only fits one substrate. For example, when sucrose (table sugar, as shown in the picture) needs to be broken down by our body, the sucrose molecule binds to the active site in the enzyme sucrase by an induced fit. When the weak bonds react with water, the substrate is hydrolyzed to its components: glucose and fructose. Once the reaction has occurred, the enzyme is available for another sucrose molecule. Enzymes are extremely effecient- they can act on thousands (or even millions!) of substrates per second!
Our environment can affect our enzymes. When our body temperature becomes to hot, it can denature the enzyme and change its specific tertiary shape. If the active site changes shape then it becomes unusable for the specific substrate that it was meant to bind to. Furthermore, when the pH or salt concentration reaches extremes, the enzyme capabilities become impaired.
Many enzymes require nonprotein helpers to help catalyze reactions. When the helper is inorganic, it is called a cofactor (such as ions of zinc, iron, or copper); when the helper is organic, it is called a coenzyme (made from vitamins or are vitamins themselves, such as vitamin B6).