All biological reactions that take place within the human body rely on enzymes. It is the power of these enzymes as catalysts that enable biological reactions to happen in a matter of milliseconds. It is thought that these biological reactions that are dependent on enzymes would take hours or days if the enzymes where not present. An interesting report was introduced in 1995 by Richard Wolfenden, Ph.D. that stated without a particular enzyme, a biological reaction that is deemed essential in the creation of the building block of DNA and RNA would take 78 million years. Another biological reaction without the presence of essential enzymes would take around 2.3 billion years or about half the age of the Earth. With the presence of the enzyme it happens in only milliseconds.

This reaction that is being reported on is essential for the biosynthesis of hemoglobin and chlorophyll. When it is catalyzed by the enzyme uroporphyrinogen decarboxylase, the rate in which the hemoglobin and the chlorophyll are produced in cells is increased by a dramatic amount of time. In knowing how long biological reactions would take without enzymes allows the biologists to realize the evolution as prolific catalysts. In the absence of a catalysts there would be basically no life around, from the smallest microbes to humans and everything in between.

Another very important biological reaction is called Transmethylation. It is where a methyl group is transformed from one compound to another. An example of this is the recovery of methionine from homocysteine. Homocysteine is an amino acid that is an amino acid cysteine, being different by an additional methylene group. By removing the methyl group. It can be recycled into methionine and also transformed into cysteine with the assistance of B-vitamins. In order to sustain enough reaction rates during metabolic stress, this biological reaction needs adequate levels of vitamin B12 and folic acid. Methyl tetrahydrofolate delivers methyl groups which make the active methyl form of the vitamin B12 that is necessary in order for methylation of homocysteine. Deficiencies of vitamin B12 or folic acid will create elevated levels of circulating homocysteine. Raised levels of homocysteine are a major risk factor for cardiovascular disease and are also associated to the metabolic syndrome known as insulin insensitivity.

Work place stress is categorized as the harmful emotional or physical response which takes place in a poorly matched job and capabilities, resources or basic needs of the worker, and it is also considered to be a biological reaction. These types of stress related disorders can entail a very wide range of conditions which include depression, anxiety, post traumatic stress, emotional strain due to fatigue or tension, maladaptive behaviors and cognitive impairments that include concentration and memory problems.