File Name: list of amino acids and their structures .zip
Amino acids are the monomers that make up proteins. Every amino acid also has another atom or group of atoms bonded to the central atom known as the R group. This R group, or side chain, gives each amino acid proteins specific characteristics, including size, polarity, and pH.
Protein , highly complex substance that is present in all living organisms. Proteins are of great nutritional value and are directly involved in the chemical processes essential for life.
They are also organ -specific; for instance, within a single organism, muscle proteins differ from those of the brain and liver. A protein is a naturally occurring, extremely complex substance that consists of amino acid residues joined by peptide bonds. Proteins are present in all living organisms and include many essential biological compounds such as enzymes, hormones , and antibodies.
Protein synthesis occurs in the ribosomes of cells. In eukaryotic cells, ribosomes are found as free-floating particles within cells and are also embedded in the rough endoplasmic reticulum , a cell organelle. Proteins are not stored for later use in animals. When an animal consumes excess proteins, they are converted into fats glucose or triglycerides and used to supply energy or build energy reserves. If an animal is not consuming sufficient protein, the body begins to break down protein-rich tissues, such as muscles , leading to muscle wasting and eventually death if the deficiency is severe.
Proteins are essential for life and are essential for a wide range of cellular activities. Proteins provide many of the structural elements of a cell, and they help to bind cells together into tissues.
A protein molecule is very large compared with molecules of sugar or salt and consists of many amino acids joined together to form long chains, much as beads are arranged on a string. There are about 20 different amino acids that occur naturally in proteins. Proteins of similar function have similar amino acid composition and sequence. Although it is not yet possible to explain all of the functions of a protein from its amino acid sequence, established correlations between structure and function can be attributed to the properties of the amino acids that compose proteins.
Plants can synthesize all of the amino acids; animals cannot, even though all of them are essential for life. Plants can grow in a medium containing inorganic nutrients that provide nitrogen , potassium , and other substances essential for growth. They utilize the carbon dioxide in the air during the process of photosynthesis to form organic compounds such as carbohydrates.
Animals, however, must obtain organic nutrients from outside sources. Because the protein content of most plants is low, very large amounts of plant material are required by animals, such as ruminants e.
Nonruminant animals, including humans, obtain proteins principally from animals and their products—e. The seeds of legumes are increasingly being used to prepare inexpensive protein-rich food see human nutrition.
The protein content of animal organs is usually much higher than that of the blood plasma. Muscles, for example, contain about 30 percent protein, the liver 20 to 30 percent, and red blood cells 30 percent. Higher percentages of protein are found in hair, bones, and other organs and tissues with a low water content.
The quantity of free amino acids and peptides in animals is much smaller than the amount of protein; protein molecules are produced in cells by the stepwise alignment of amino acids and are released into the body fluids only after synthesis is complete.
The high protein content of some organs does not mean that the importance of proteins is related to their amount in an organism or tissue ; on the contrary, some of the most important proteins, such as enzymes and hormones , occur in extremely small amounts.
The importance of proteins is related principally to their function. All enzymes identified thus far are proteins. Enzymes, which are the catalysts of all metabolic reactions, enable an organism to build up the chemical substances necessary for life—proteins, nucleic acids , carbohydrates, and lipids —to convert them into other substances, and to degrade them.
Life without enzymes is not possible. There are several protein hormones with important regulatory functions. In all vertebrates, the respiratory protein hemoglobin acts as oxygen carrier in the blood , transporting oxygen from the lung to body organs and tissues. A large group of structural proteins maintains and protects the structure of the animal body. Protein Article Media Additional Info. Article Contents.
Print print Print. Table Of Contents. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Facebook Twitter. Give Feedback External Websites. Let us know if you have suggestions to improve this article requires login. External Websites. Genetic Home Reference - What are proteins and what do they do? Articles from Britannica Encyclopedias for elementary and high school students.
Daniel E. Editor, Science magazine, — See Article History. Alternative Title: macromolecular peptide. Top Questions. The molecular structure of a peptide a small protein consists of a sequence of amino acids.
Legumes—such as beans, lentils, and peas—are high in protein and contain many essential amino acids. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now. Each chain is attached to a heme group composed of porphyrin an organic ringlike compound attached to an iron atom.
These iron-porphyrin complexes coordinate oxygen molecules reversibly, an ability directly related to the role of hemoglobin in oxygen transport in the blood. Load Next Page.
All of the proteins on the face of the earth are made up of the same 20 amino acids. Linked together in long chains called polypeptides, amino acids are the building blocks for the vast assortment of proteins found in all living cells. All amino acids have the same basic structure, which is shown in Figure 2. With the exception of glycine, which has an R-group consisting of a hydrogen atom, all of the amino acids in proteins have four different groups attached to them and consequently can exist in two mirror image forms, L and D. With only very minor exceptions, every amino acid found in cells and in proteins is in the L configuration. There are 22 amino acids that are found in proteins and of these, only 20 are specified by the universal genetic code. The others, selenocysteine and pyrrolysine use tRNAs that are able to base pair with stop codons in the mRNA during translation.
Hydrophobic - aliphatic Hydrophobic - aromatic Neutral - polar side chains Acidic. Amino acids are the compounds or building blocks that make up peptides and proteins. Each amino acid is structured from an amino group and a carboxyl group bound to a tetrahedral carbon. Amino acids differ from each other with respect to their side chains, which are referred to as R groups. The R group for each of the amino acids will differ in structure, electrical charge, and polarity. Refer to the charts and structures below to explore amino acid properties, types, applications, and availability. Alanine , Ala, A.
twenty essential amino acids and a tripeptide have been presented. shown to be sums of the appropriate covalent radii of the adjacent atoms, and their  ebezpieczni.orgpdf.
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Basic Structure of Amino Acids. Introduction Essential amino acids Why learn this?
An essential amino acid , or indispensable amino acid , is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms, the nine amino acids humans cannot synthesize are phenylalanine , valine , threonine , tryptophan , methionine , leucine , isoleucine , lysine , and histidine. Six other amino acids are considered conditionally essential in the human diet, meaning their synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress. Six amino acids are non-essential dispensable in humans, meaning they can be synthesized in sufficient quantities in the body. These six are alanine , aspartic acid , asparagine , glutamic acid , serine ,  and selenocysteine considered the 21st amino acid. Pyrrolysine , which is proteinogenic only in certain microorganisms, is not used by and therefore non-essential for most organisms, including humans.
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