Metabolism consists of all the biochemical processes that occur in living cells. These processes or metabolic reactions can generally be classified as either anabolic or catabolic. Anabolic means to build, catabolic means to breakdown.
Humans obtain energy through consuming a healthy, well-balanced diet. The ingested macronutrients —carbohydrates, fats, and proteins— are ultimately broken down in order to release the stored energy in different pathways.
There are many metabolic pathways, processes, or reactions that are involved in the synthesis or degradation of carbohydrates and compounds formed from them. Please note that most of these pathways are not specific to carbohydrates only. For example, in gluconeogenesis certain (glucogenic) amino acids are used for synthesizing glucose if needed.
There are many metabolic pathways, processes, or reactions that are involved in the synthesis or degradation of lipids and compounds derived from them. Excess intake of energy-containing nutrients, including the consumption of excess carbohydrates and excess protein as well as eating too much fat in one's diet can lead to 'fat production' or lipogenesis, whereby the human body is designed to almost have unlimited fat store capabilities.
There are four protein metabolic pathways that will be covered in this section: Transamination -transfer of an amino group from one amino acid to another Deamination -removal of an amino group, normally from an amino acid. Gluconeogenesis -synthesis of glucose from a non-carbohydrate source. Protein Turnover/Degradation -liberation of amino acids from proteins.
The other energy source is alcohol. The alcohol we consume contains two carbons and is known as ethanol. Ethanol is passively absorbed by simple diffusion into the enterocyte. Ethanol metabolism occurs primarily in the liver, but 10-30% is estimated to occur in the stomach. For the average person, the liver can metabolize the amount of ethanol in one drink (1/2 ounce) per hour. There are three ways that alcohol is metabolized in the body.
Thousands of metabolic reactions are taking place in your cells generate more than just energy; metabolic waste products such as water, carbon dioxide, and nitrogen-containing compounds are produced as well and must be excreted.