What Are The 20 Amino Acids In The Human Body

What Are The 20 Amino Acids In The Human Body – Proteins are among the most abundant organic molecules in living systems and have the most diverse functions of all macromolecules. Proteins can be structural, regulatory, contractile, or protective; they may serve in transport, storage or membranes; or may contain toxins or enzymes. Each cell in a living system may contain thousands of proteins, each with a unique function. Their structures, like their functions, are very diverse. However, they are all polymers of amino acids arranged in a linear sequence.

Figure 1. Amino acids have a central asymmetric carbon to which an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group) are attached.

What Are The 20 Amino Acids In The Human Body

What Are The 20 Amino Acids In The Human Body

Amino acids are the monomers that make up proteins. Each amino acid has the same basic structure, consisting of a central carbon atom, as well as an alpha (

Amino Acid Molecules Ball And Stick Structure Stock Vector

) carbon bonded to an amino group (NH2), a carboxyl group (COOH) and a hydrogen atom. Each amino acid has another atom or group of atoms attached to the central atom, also known as the R group (Figure 1).

The name “amino acid” comes from the fact that they contain both an amino group and a carboxyl-acid group in their basic structure. As mentioned, there are 20 amino acids in proteins. Nine of these are considered essential amino acids in the human body because the human body cannot produce them and they must be obtained from food.

Figure 2. There are 20 common amino acids commonly found in proteins, each with a different R group (variant group) that determines its chemical nature.

Which amino acid categories would you expect to find on the surface of the soluble protein and which on the inside? What distribution of amino acids would you expect in a protein embedded in a lipid bilayer?

Structure Of Amino Acids And Proteins

Polar and charged amino acid residues (remaining after the formation of peptide bonds) are found on the surface of soluble proteins that can interact with water, while non-polar (eg amino acid side chains) are found on the surface of more proteins. the inner part where they are separated from the water. In membrane proteins, nonpolar and hydrophobic amino acid side chains bind to the hydrophobic tails of phospholipids, while polar and charged amino acid side chains interact with polar headgroups or aqueous solution. However, there are exceptions. Sometimes the positively and negatively charged amino acid side chains interact with each other in the interior of the protein, and polar or charged amino acid side chains can be found interacting with the ligand in the ligand binding pocket.

The chemical nature of the side chain determines the nature of the amino acid (ie, is it acidic, basic, polar, or nonpolar). For example, the amino acid glycine has a hydrogen atom as the R group. Amino acids such as valine, methionine, and alanine are nonpolar or hydrophobic, while amino acids such as serine, threonine, and cysteine ​​are polar and have hydrophilic side chains. The side chains of lysine and arginine are positively charged and hence these amino acids are also known as essential amino acids. Proline has an R group attached to an amino group, forming a ring-like structure. Proline is an exception to the standard amino acid structure because its amino group is not separated from the side chain (Figure 2).

Amino acids are represented by a single capital letter or a three-letter abbreviation. For example, valin is known by the letter V or the three-letter val symbol. Just as some fatty acids are essential to the diet, so are some amino acids. They are known as essential amino acids, and in humans they include isoleucine, leucine, and cysteine. Essential amino acids refer to those that are necessary for building proteins in the body, even though they are not produced by the body; which amino acids are essential varies from organism to organism.

What Are The 20 Amino Acids In The Human Body

Figure 3. Peptide bond formation is a dehydration synthesis reaction. The carboxyl group of one amino acid is linked to the amine group of the incoming amino acid. A water molecule is released in the process.

Amino Acid Chart

The sequence and number of amino acids ultimately determines the shape, size and function of the protein. Each amino acid is attached to another amino acid by a covalent bond known as a peptide bond, which is formed by a dehydration reaction. The carboxyl group of an amino acid and the amine group of an incoming amino acid combine to release a molecule of water. The resulting bond is a peptide bond (Figure 3).

The products formed from such connections are called peptides. As more amino acids are added to this growing chain, the resulting chain is known as a polypeptide. Each polypeptide has a free amino group at one end. This end is called the N terminus or amino terminus and the other end has a free carboxyl group known as the C or carboxyl terminus. Although the terms polypeptide and protein are sometimes used interchangeably, a polypeptide is technically a polymer of amino acids, while the term protein is used for a polypeptide or polypeptides of distinct shape that are joined together, often with non-peptide prosthetic groups. , and has a unique function. After protein synthesis (translation), most proteins are modified. These are known as post-translational modifications. They may undergo degradation, phosphorylation, or require the addition of other chemical groups. Only after these changes the protein becomes fully functional.

Cytochrome c is an important component of the electron transport chain, part of cellular respiration, and it is normally found in the cell organelle, the mitochondria. This protein has a heme prosthetic group, and the central heme ion is alternately reduced and oxidized during electron transfer. Because this important protein’s role in cellular energy production is so important, it has changed little over millions of years. Protein sequencing showed a significant amount of cytochrome c amino acid sequence homology between different species; in other words, evolutionary relatedness can be assessed by measuring the similarities or differences between the DNA or protein sequences of different species.

Scientists have determined that human cytochrome c has 104 amino acids. For every cytochrome c molecule from the various organisms sequenced to date, 37 of these amino acids appear in the same position in all samples of cytochrome c. This suggests a possible common ancestor. Comparing human and chimpanzee protein sequences found no sequence differences. When human and rhesus monkey sequences were compared, the only difference found was in one amino acid. In another comparison, human-to-yeast sequences show a difference at position 44. Protein amino acids are amino acids that are biosynthetically incorporated into proteins during translation. The word “proteinogic” means “protein maker”. There are 22 genetically encoded (proteinological) amino acids in known life, 20 in the standard genetic code and an additional 2 (celocysteine ​​and pyrrolysine) that can be incorporated by special translational mechanisms.

Complete Mcat Amino Acids Proteins Guide

In contrast, nonprotein amino acids are amino acids that are not incorporated into proteins (such as GABA, L-DOPA, or triiodothyronine), are incorporated incorrectly instead of the encoded amino acid, or are not directly and exclusively produced by the standard cell. machine (as hydroxyproline). The latter often occurs as a result of post-translational modification of proteins. Some non-protein amino acids are incorporated into non-ribosomal peptides synthesized by non-ribosomal peptide synthetases.

Both eukaryotes and prokaryotes can incorporate cylocysteine ​​into their proteins through a nucleotide sequence known as a SECIS element, which directs the cell to translate the nearby UGA codon as cylocysteine ​​(UGA is normally a stop codon). In some methanogenic prokaryotes, the UAG codon (usually a stop codon) can also be pyrrolyzed.

Eukaryotes have only 21 protein amino acids, 20 of the standard genetic code, plus cylocysteine. Humans can synthesize 12 of these from each other or from other intermediary metabolic molecules. The remaining nine must be consumed (usually as their protein derivatives) and are therefore called essential amino acids. The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, philalanine, threonine, tryptophan, and valine (ie H, I, L, K, M, F, T, W, V).

What Are The 20 Amino Acids In The Human Body

Protein amino acids have been found to be associated with a set of amino acids that can be recognized by ribozyme autoaminoacylation systems.

Amino Acid Structure Molecular Model Kit 20 Essential Amino Acids, From Indigo

Thus, non-protein amino acids could have been excluded by the conditional evolutionary success of nucleotide-based life forms. Other reasons have been proposed to explain why certain specific non-protein amino acids are generally not incorporated into proteins; for example, ornithine and homoserine cyclize against the peptide backbone and degrade the protein with relatively short half-lives, while others are toxic because they can be mistakenly incorporated into proteins, such as the arginine analog canavanine.

The evolutionary selection of certain protein amino acids from the primordial soup is due to their better incorporation into the polypeptide chain than non-protein amino acids.

Below are the structures and abbreviations of the 21 amino acids directly encoded for protein synthesis by the genetic code of eukaryotes. The structures given below are standard

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