Cell components need to be built and assembled from organic material. Most of the cell components are made from polymers. The synthesis of polymers requires energy.Reactions that build up cellular components are called anabolic processes. Reactions that break down molecules are catabolic processes.Cellular reactions do not happen in isolation. They are usually part of metabolic pathways. The reactions happen ordinarily at a slow rate but the rate of reaction is influenced by environmental factors such as temperature, pressure and the concentration of substrates. Catalysts can increase the rate of reaction whilst maintaining a stable pH and temperature and reduce the need for higher temperatures.Enzymes are biological catalysts. Enzymes can speed up the reactions to a maximum rate Vmax. Enzymes also can control the order in which reactions happen to create biochemical pathways.