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What is amino acids and vitamins

Amino acids function: building blocks

of proteins

Proteins are of primary importance to the continuing functioning of life on Earth. Proteins catalyze the vast majority of

chemical reactions that occur in the cell. They provide many of the structural elements of a cell, and they help to bind

cells together into tissues. Some proteins act as contractile elements to make movement possible. Others are responsible for

the transport of vital materials from the outside of the cell (“extracellular”) to its inside (“intracellular”).

Proteins, in the form of antibodies, protect animals from disease and, in the form of interferon, mount an intracellular

attack against viruses that have eluded destruction by the antibodies and other immune system defenses. Many hormones are

proteins. Last but certainly not least, proteins control the activity of genes (“gene expression”).

This plethora of vital tasks is reflected in the incredible spectrum of known proteins that vary markedly in their

overall size, shape, and charge. By the end of the 19th century, scientists appreciated that, although there exist many

different kinds of proteins in nature, all proteins upon their hydrolysis yield a class of simpler compounds, the building

blocks of proteins, called amino acids. The simplest amino acid is called glycine, named for its sweet taste (glyco, “sugar

”). It was one of the first amino acids to be identified, having been isolated from the protein gelatin in 1820. In the

mid-1950s scientists involved in elucidating the relationship between proteins and genes agreed that 20 amino acids (called

standard or common amino acids) were to be considered the essential building blocks of all proteins. The last of these to be

discovered, threonine, had been identified in 1935.

Chirality

All the amino acids but glycine are chiral

molecules. That is, they exist in two optically active asymmetric forms (called enantiomers) that are the mirror images of

each other. (This property is conceptually similar to the spatial relationship of the left hand to the right hand.) One

enantiomer is designated D and the other L. It is important to note that the amino acids found in proteins almost always

possess only the L-configuration. This reflects the fact that the enzymes responsible for protein synthesis have evolved to

utilize only the L-enantiomers. Reflecting this near universality, the prefix L is usually omitted. Some D-amino acids are

found in microorganisms, particularly in the cell walls of bacteria and in several of the antibiotics. However, these are not

synthesized in the ribosome.

Acid-base properties

Another important feature of free amino acids is the existence of both a basic and an acidic group at the α-carbon.

Compounds such as amino acids that can act as either an acid or a base are called amphoteric. The basic amino group typically

has a pKa between 9 and 10, while the acidic α-carboxyl group has a pKa that is usually close to 2 (a very low value for

carboxyls). The pKa of a group is the pH value at which the concentration of the protonated group equals that of the

unprotonated group. Thus, at physiological pH (about 7–7.4), the free amino acids exist largely as dipolar ions or

“zwitterions” (German for “hybrid ions”; a zwitterion carries an equal number of positively and negatively charged

groups). Any free amino acid and likewise any protein will, at some specific pH, exist in the form of a zwitterion. That is,

all amino acids and all proteins, when subjected to changes in pH, pass through a state at which there is an equal number of

positive and negative charges on the molecule. The pH at which this occurs is known as the isoelectric point (or isoelectric

pH) and is denoted as pI. When dissolved in water, all amino acids and all proteins are present predominantly in their

isoelectric form. Stated another way, there is a pH (the isoelectric point) at which the molecule has a net zero charge

(equal number of positive and negative charges), but there is no pH at which the molecule has an absolute zero charge

(complete absence of positive and negative charges). That is, amino acids and proteins are always in the form of ions; they

always carry charged groups. This fact is vitally important in considering further the biochemistry of amino acids and

proteins.

What are vitamins, and how do they work?

Vitamins are organic compounds that people need in small quantities. Most vitamins need to come from food because the

body either does not produce them or produces very little. Each organism has different vitamin requirements. For example,

humans need to get vitamin C from their diets — while dogs can produce all the vitamin C that they need.

For humans, vitamin D is not available in large enough quantities in food. The human body synthesizes the vitamin when

exposed to sunlight, and this is the best source of vitamin D. Different vitamins play different roles in the body, and a

person requires a different amount of each vitamin to stay healthy.

This article explains what vitamins are, what they do, and which foods are good sources. Follow the links in blue below

for more information about each vitamin. Vitamins are organic substances present in minute amounts in natural foodstuffs.

Having too little of any particular vitamin may increase the risk of developing certain health issues. A vitamin is an

organic compound, which means that it contains carbon. It is also an essential nutrient that the body may need to get from

food.

Fat-soluble vitamins

Vitamins A, D, E, and K are fat-soluble. The body storesTrusted Source fat-soluble vitamins in fatty tissue and the

liver, and reserves of these vitamins can stay in the body for days and sometimes months. Dietary fats help the body absorb

fat-soluble vitamins through the intestinal tract.

Water-soluble vitamins

Water-soluble vitamins do not stayTrusted Source in the body for long and cannot be stored. They leave the body via the

urine. Because of this, people need a more regular supply of water-soluble vitamins than fat-soluble ones.