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A negative nitrogen balance can be used as part of a clinical evaluation of malnutrition. [3] Nitrogen balance is a method traditionally used to measure dietary protein requirements. [4] This approach necessitates the meticulous collection of all nitrogen inputs and outputs to ensure comprehensive accounting of nitrogen exchanges. [5]
Proteins were first described by the Dutch chemist Gerardus Johannes Mulder and named by the Swedish chemist Jöns Jacob Berzelius in 1838. [4] [5] Mulder carried out elemental analysis of common proteins and found that nearly all proteins had the same empirical formula, C 400 H 620 N 100 O 120 P 1 S 1. [6]
This value is known as the "crude protein" content. The use of correct conversion factors is heavily debated, specifically with the introduction of more plant-derived protein products. [20] However, on food labels the protein is calculated by the nitrogen multiplied by 6.25, because the average nitrogen content of proteins is about 16%.
Proteins were found to yield amino acids after enzymatic digestion or acid hydrolysis. In 1902, Emil Fischer and Franz Hofmeister independently proposed that proteins are formed from many amino acids, whereby bonds are formed between the amino group of one amino acid with the carboxyl group of another, resulting in a linear structure that ...
Found in carbohydrates, lipids, nucleic acids, and proteins. Hydrogen 10% 10% Found in water, carbohydrates, lipids, nucleic acids, and proteins. Nitrogen 1% 4% Found in nucleic acids, proteins, some lipids (e.g. sphingolipids) and some polysaccharides (e.g. chitin) Oxygen 77% 63% Found in water, carbohydrates, lipids, nucleic acids, and proteins.
The elements listed below as "Essential in humans" are those listed by the US Food and Drug Administration as essential nutrients, [9] as well as six additional elements: oxygen, carbon, hydrogen, and nitrogen (the fundamental building blocks of life on Earth), sulfur (essential to all cells) and cobalt (a necessary component of vitamin B 12).
It does not, however, give a measure of true protein content, as it measures nonprotein nitrogen in addition to the nitrogen in proteins. This is evidenced by the 2007 pet food incident and the 2008 Chinese milk powder scandal, when melamine, a nitrogen-rich chemical, was added to raw materials to fake high protein contents. Also, different ...
The amount of nitrogen in a chemical substance can be determined by the Kjeldahl method. [21] In particular, nitrogen is an essential component of nucleic acids, amino acids and thus proteins, and the energy-carrying molecule adenosine triphosphate and is thus vital to all life on Earth. [20]