Protein

Proteins are large biological molecules consisting of one or more chains of amino acids. Proteins perform many functions within the living organism., including catalyzing metabolic reactions, replicating DNA, responding to stimuli and transporting molecules from one location to another.
Catalysis of metabolic reaction is an important role that proteins play. Enzymes play important roles in these reactions. For example digestion is a reaction used to sustains the life of an organism in which many reactions take place. These enzymatic-catalyzed reactions allow an organism to grow and reproduce, maintain their structures and respond to the environment. Responding to the environment can be for example the human body fighting off a bacteria. Enzymes are responsible for the thousands of metabolic processes used to sustain life. Digestion of food and synthesis of DNA are two purposes of enzymes. Enzymatic reactions, the substrate are molecules at the beginning of the process and are converted into different molecules which are then called products. Enzymes are usually very specific as to which reactions they catalyze and the substrates that are involved in these reactions.
By enzyme catalysis providing an alternative reaction route the enzyme can reduce the energy required to reach the highest energy transition state of the reaction. The reduction of activation energy increases the number of reactant molecules with enough energy to reach the activation energy and form the product. Enzymes let organisms drive reactions that require energy that will not occur by themselves by coupling them to spontaneous reactions that release energy. Enzymes act as catalysts that allow the reactions to proceed more rapidly. Enzymes also allow the regulation of metabolic pathways in response to the changes in the cells environment or to signal from other cells.
The word metabolism can also refer to any chemical reaction that occurs in living organisms like digestion. Along with digestion the transportation of substances into and between different cells is another form of metabolism, the reaction within the cells is called intermediary metabolism. The two categories that metabolism is divided into is catabolism and anabolism. The catabolism process is one that breaks down organic matter and harvests energy by way of cellular respiration. The anabolism process is one that uses energy to construct components of cells such as proteins and nucleic acids (DNA, RNA). Metabolism is organized into metabolic pathways in which through a series of steps transforms one chemical into another.
The second action of a protein is DNA replication. This occurs by producing two identical copies from the original DNA molecule. the two strands of the original DNA molecule serve as a templet for the complementary strand. This process is referred to as semiconservative replication. There is cellular proofreading and error-checking mechanisms for perfect replication. The genome is the beginning of the DNA replication process in the cell. The unwinding of the DNA at the origin and synthesis result in replication forks growing bidirectionally from the origin. A number of proteins are associated with the replication fork which assist in the initiation and continuation of DNA synthesis. In vitro or artificial replication of DNA can be performed.
Cell signaling or responding to stimuli is another function of protein. This is a system of communication for cellular activities and coordinates cell actions. These actions must take place for development, tissue repair, and immunity as well as normal tissue homeostasis. Errors in these information processes by the cells may lead to diabetes, autoimmunity and cancer. If the information of cell signaling is put to use scientist should be able in theory to create artificial tissues.