Roughly 96 percent of the mass of the human body is made up of just four elements: oxygen, carbon, hydrogen and nitrogen, with a lot of that in the form of water. The remaining 4 percent is a sparse sampling of the periodic table of elements.
Some of the more prominent representatives are called macro nutrients, whereas those appearing only at the level of parts per million or less are referred to as micronutrients.
These nutrients perform various functions, including the building of bones and cell structures, regulating the body's pH, carrying charge, and driving chemical reactions.
The FDA has set a reference daily intake for 12 minerals (calcium, iron, phosphorous, iodine, magnesium, zinc, selenium, copper, manganese, chromium, molybdenum and chloride). Sodium and potassium also have recommended levels, but they are treated separately.
However, this does not exhaust the list of elements that you need. Sulfur is not usually mentioned as a dietary supplement because the body gets plenty of it in proteins.
And there are several other elements — such as silicon, boron, nickel, vanadium and lead — that may play a biological role but are not classified as essential.
"This may be due to the fact that a biochemical function has not been defined by experimental evidence," said Victoria Drake from the Linus Pauling Institute at Oregon State University.
Sometimes all that is known is that lab animals performed poorly when their diets lacked a particular non-essential element. However, identifying the exact benefit an element confers can be difficult as they rarely enter the body in a pure form.
"We don't look at them as single elements but as elements wrapped up in a compound," said Christine Gerbstadt, national spokesperson for the American Dietetic Association.
A normal diet consists of thousands of compounds (some containing trace elements) whose effects are the study of ongoing research. For now, we can only say for certain what 20 or so elements are doing. Here is a quick rundown, with the percentage of body weight in parentheses.
Oxygen (65%) and hydrogen (10%) are predominantly found in water, which makes up about 60 percent of the body by weight. It's practically impossible to imagine life without water.
Carbon (18%) is synonymous with life. Its central role is due to the fact that it has four bonding sites that allow for the building of long, complex chains of molecules. Moreover, carbon bonds can be formed and broken with a modest amount of energy, allowing for the dynamic organic chemistry that goes on in our cells.
Nitrogen (3%) is found in many organic molecules, including the amino acids that make up proteins, and the nucleic acids that make up DNA.
Calcium (1.5%) is the most common mineral in the human body — nearly all of it found in bones and teeth. Ironically, calcium's most important role is in bodily functions, such as muscle contraction and protein regulation. In fact, the body will actually pull calcium from bones (causing problems like osteoporosis) if there's not enough of the element in a person's diet.
Phosphorus (1%) is found predominantly in bone but also in the molecule ATP, which provides energy in cells for driving chemical reactions.
Potassium (0.25%) is an important electrolyte (meaning it carries a charge in solution). It helps regulate the heartbeat and is vital for electrical signaling in nerves.
Sulfur (0.25%) is found in two amino acids that are important for giving proteins their shape.
Sodium (0.15%) is another electrolyte that is vital for electrical signaling in nerves. It also regulates the amount of water in the body.
Chlorine (0.15%) is usually found in the body as a negative ion, called chloride. This electrolyte is important for maintaining a normal balance of fluids.
Magnesium (0.05%) plays an important role in the structure of the skeleton and muscles. It also is necessary in more than 300 essential metabolic reactions.
Iron (0.006%) is a key element in the metabolism of almost all living organisms. It is also found in hemoglobin, which is the oxygen carrier in red blood cells. Half of women don't get enough iron in their diet.
Fluorine (0.0037%) is found in teeth and bones. Outside of preventing tooth decay, it does not appear to have any importance to bodily health.
Zinc (0.0032%) is an essential trace element for all forms of life. Several proteins contain structures called "zinc fingers" help to regulate genes. Zinc deficiency has been known to lead to dwarfism in developing countries.
Copper (0.0001%) is important as an electron donor in various biological reactions. Without enough copper, iron won't work properly in the body.
Iodine (0.000016%) is required for making of thyroid hormones, which regulate metabolic rate and other cellular functions. Iodine deficiency, which can lead to goiter and brain damage, is an important health problem throughout much of the world.
The most significant chemical reactions
Metabolic pathways in human organism form vast network of more or less interconnected reactions that often share common intermediate products. Chemical conversions, which occur during the chemical reactions, can be divided according to the general mechanism, shared by all substances undergoing that particular reaction. For example, decarboxylationreactions involve splitting off a CO2 molecule from the carboxyl group and its substrates include various carboxylic acids.
In this subchapter, we will speak about the most important types of chemical reactions with typical examples taken from human metabolic pathways.
Alcohols, carbonyl compounds and carboxylic acids
Alcohols, carbonyl compounds and carboxylic acids form an important group of substances involved in many chemical reactions of intermediate metabolism.
Alcohols are characterized by the presence of OH- functional group. Depending on the number of these groups in the molecule, alcohols can by mono-, di- or polyhydric. Another division is based on the nature of a carbon atom to which an OH- group is attached: primary(R-CH2-OH), secondary (R1-CH(OH)-R2) and tertiary (C-R1R2R3(OH)) alcohols.
Aldehydes and ketones together, for a group of carbonyl compounds. Their functional groups are –CHO and C=O, respectively.
Carboxylic acids, characterised by the presence of –COOH group, and their derivatives are probably the most important members of this group of substances.
Alcohols, carbonyl compounds and carboxylic acids participate in many reactions – among the most significant are:
1) The formation of anions and acyls, derived from carboxylic acids
2) Dehydrogenations and hydrogenations (oxidations and reductions)
3) Esterifications
1) The formation of anions and acyls, derived from carboxylic acids
Carboxyl group is capable of dissociation, the extent of which, for a particular acid, is expressed by dissociation constant. In general, carboxylic acids belong to weak acids, which means that they dissociate only partially. The resulting anion (with -COO- group) is termedacetate.
After splitting off the OH- group from carboxyl an acyl is formed.
2) Dehydrogenations and hydrogenations (oxidations and reductions)
Dehydrogenation is a chemical reaction leading to the elimination of –H atom from the molecules. The hydrogen atom obtained in this process can be subsequently used to create a proton gradient across the mitochondrial membrane in order to gain energy (ATP). The incorporation of the hydrogen into the molecule is termed hydrogenation. Hydrogenations and dehydrogenations occur during:
a) The oxidation of simple bonds to double bonds
b) The reciprocal conversions of alcohols – carbonyl compounds – carboxylic acids
a) The oxidation of simple bonds to double bonds
The general reaction scheme is as follows:
-CH2-CH2- ↔ -CH=CH- + 2H+ + 2e-
Such reactions are abundant in Krebs cycle, β-oxidation of fatty acids or desaturation reactions (producing unsaturated fatty acids).
b) The reciprocal conversions of alcohols – carbonyl compounds – carboxylic acids
This threesome of organic compounds forms a series that differ in the degree of oxidation(or reduction). General scheme of their interconversion is as follows (conversion towards the carbonyl compound and carboxylic acid is oxidation, in opposite direction it is a reduction):
1. Primary alcohol ↔ aldehyde ↔ carboxylic acid
R-CH2-OH ↔ R-CHO ↔ R-COOH
2. Secondary alcohol ↔ ketone
R1-CH(OH)-R2 ↔ R1-CO-R2
3. Tertiary alcohol – cannot be oxidised
As an example of oxidation, we can take the conversion of glycerol-3-phosphate todihydroxyacetone phosphate (DHA-P), with FAD as a cofactor, through which a glycerol enters the metabolic pathways of glycolysis or gluconeogenesis (depending on the actual needs of the organism).
3) Esterification
Esterification is a reaction between carboxylic acid and alcohol, creating an ester and awater molecule:
R1-OH + R-COOH → R1-O-(C=O)-R + H2O
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