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Proteins |
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| Proteins are a class of organic compounds which are present in and vital to every living cell. Structurally, proteins are large molecules composed of one or more chains of varying amounts of the same 22 amino acids that are linked by peptide bonds. In general proteins fold into two broad classes of structure termed, globular proteins or fibrous proteins. Globular proteins are compactly folded and coiled. As indicated by their name, globular proteins are also characterized by their spheroid, compact
structures. The fibrous proteins are composed of polypeptides that are often highly cross-linked by various types of bonding to yield tough and water-insoluble structural proteins such as hair, skin, collagen, tendons, and silk. Some fibrous proteins are also involved in constructing the important cellular components known as microtubules. Proteins contain carbon, hydrogen, and oxygen like the carbohydrates and lipids, but they also contain nitrogen and often sulfur and phosphorus. Proteins are important constituents of all cells and tissues. Proteins are made from amino acids. There are many different kinds of proteins in the body with many different functions.
Proteins are one of the classes of bio-macromolecules, alongside polysaccharides, lipids, and nucleic acids, that make up the primary constituents of living things. Protein is the most abundant class of all biological molecules, comprising about 50 percent of cellular dry weight. Each protein is characterized by a unique and invariant amino acid sequence. Proteins include enzymes, hormones, and antibodies. They are made up of strings of amino acids. Proteins that catalyze chemical reactions are called enzymes. The largest functional group of proteins is the enzymes. Enzymes catalyze biological reactions, increasing the rate of such reactions, and allowing them to occur at temperatures that are conducive to life. Enzymes play an essential role in unzipping the DNA double helix, and so enabling it to reproduce and to send out the instructions for building proteins. Enzymes act upon a substrate, changing it into a product. The catalytic properties and specificity of an enzyme is determined by the shape of its active site, which depends upon the tertiary structure of the protein. Enzymes help the body's chemistry work better and more quickly. Each enzyme usually has its own chemical job to do such as helping to change starch into glucose (sugar).
Proteins are polymers of amino acids that are synthesized in the cell. There are 20 different amino acids that are found in proteins. All have acid and amino groups, and a central carbon atom. The 20 are distinguished from one another by the presence of a side chain. Amino acids are the basic structural building units of proteins. They form short polymer chains called peptides or polypeptides which in turn form structures called proteins. To form protein, the amino acids are linked by dehydration synthesis to form peptide bonds. The chain of amino acids is also known as a polypeptide. Some proteins contain only one polypeptide chain while others, such as hemoglobin, contain several polypeptide chains all twisted together. In addition to protein synthesis, amino acids have other biologically important roles. Some of the 20 standard amino acids are called essential amino acids, because they cannot be synthesized by the body from other compounds through chemical reactions, but instead must be taken in with food. In humans, the essential amino acids are lysine, leucine, isoleucine, methionine, phenylalanine, threonine, tryptophan, valine, and (in children) histidine and arginine. Numerous non-standard amino acids are also biologically important: GABA (another neurotransmitter), carnitine (used in lipid transport within a cell), ornithine, citrulline, homocysteine, hydroxyproline, hydroxylysine, and sarcosine. |
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Biological functions in human health |
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| Proteins are used for energy, communication, ezymatic activity, communication, transport, and many other things. Some proteins have structural functions, forming the support framework for cells or tissues. Collagen forms fibers that contribute to the structure of connective tissues in the body, such as cartilage, tendons, ligaments, and bone. Collagen also contributes to the connective tissue of skin and blood vessels. Some proteins act as transporters within the body. Hhemoglobin carries oxygen in the circulatory system from the lungs to the tissues of the body. Certain proteins are contractile, allowing for function in tissue movement, and muscle contraction. Actin and myosin are the main proteins involved in muscle contraction.
Proteins are involved in practically every function performed by a cell, including regulation of cellular functions such as signal transduction and metabolism. Many proteins are involved in intercellular communication. Proteins are involved in controlling the metabolism of cells, controlling the structure and movement of cells and larger structures and coordinating the response of cells to internal and external factors. Protein is the main component of muscles, organs, and glands. Every living cell and all body fluids, except bile and urine, contain protein. The cells of muscles, tendons, and ligaments are maintained with protein.
Proteins are components of receptors on cell surfaces that bind hormone molecules from the blood stream, resulting in changes in cell behavior. Proteins are important in our defense mechanism as antibodies that recognize and bind to foreign materials that enter our systems. In the form of skin, hair, callus, cartilage, muscles, tendons and ligaments, proteins hold together, protect, and provide structure to the body of a multicelled organism. In the form of enzymes, hormones, antibodies, and globulins, they catalyze, regulate, and protect the body chemistry. In the form of hemoglobin, myoglobin and various lipoproteins, they effect the transport of oxygen and other substances within an organism. |
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Protein nutrition sources |
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| A certain amount of protein must be consumed through the diet in order for human nutritional needs to be met. Proteins are usually considered to exist in both complete and incomplete forms. If the protein in a food supplies enough of the essential amino acids, it is called a complete protein. If the protein of a food does not supply all the essential amino acids, it is called an incomplete protein. Sources of complete proteins contain all of the amino acids that the human body is unable to manufacture itself, while incomplete proteins lack one or more of the essential amino acids. All meat and other animal products are sources of complete proteins. Certain food such as meat, fish, eggs, and beans are good sources of protein, necessary for the growth and repair of human tissue. Popular meat and milk-replacement products contain soy, which is a "complete" protein as well. Soy is also very rich in protein. Plant proteins can be combined to include all of the essential amino acids and form a complete protein. Examples of combined, complete plant proteins are rice and beans, milk and wheat cereal, and corn and beans. |
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Protein deficiency |
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| Protein deficiency can lead a number of symptoms including irregular hormonal activity, hair loss, decreased muscle mass, fatigue, resistance to insulin, and decreased body temperature. Severe protein deficiency, encountered only in times of famine, is fatal. The disease kwashiorkor being an extreme form of protein deficiency. Kwashiorkor is characterized by generalized edema; "flaky paint" dermatosis; thinning, decoloration, and reddening of the hair; enlarged fatty liver; and petulant apathy in addition to retarded growth. Since the immune system is dependent upon adequate proteins, protein deficiency can manifest as recurrent or severe infections. Protein deficiency in children results in growth retardation, mental apathy and irritability, weakness and muscle atrophy, edema, hair loss, deformity of skeletal bone, anorexia, vomiting and diarrhea. |
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Side effects |
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| Excessive bodily levels of protein are likewise associated with hazardous effects. Excess protein can cause problems as well, such as causing the immune system to overreact, liver dysfunction from increased toxic residues, bone loss due to increased acidity in the blood, foundering (foot problems) in horses, and has also been linked to obesity. A diet high in meat could lead to high cholesterol or other diseases, such as gout. Another potential problem is that a high-protein diet may put a strain on the kidneys. Extra waste matter, which is the end product of protein metabolism, is excreted in the urine. Proteins can often figure in allergies and allergic reactions to certain foods. This is because the structure of each form of protein is slightly different, and some may trigger a response from the immune system while others are perfectly safe. Many people are allergic to casein, the protein in milk; gluten, the protein in wheat and other grains; the particular proteins found in peanuts; or those in shellfish or other seafoods. It is extremely unusual for the same person to adversely react to more than two different types of proteins. |
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