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Proteins (pron.: /ˈproʊˌtiːnz/ or /ˈproʊti.ɨnz/) are large biological molecules consisting of one or more chains of amino acids. Proteins perform a vast array of functions within living organisms, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of theirgenes, and which usually results in folding of the protein into a specific three-dimensional structure that determines its activity.
A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the genetic code specifies 20 standard amino acids; however, in certain organisms the genetic code can include selenocysteine and—in certainarchaea—pyrrolysine. Shortly after or even during synthesis, the residues in a protein are often chemically modified by posttranslational modification, which alters the physical and chemical properties, folding, stability, activity, and ultimately, the function of the proteins. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors. Proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes.
Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms and participate in virtually every process within cells. Many proteins are enzymes that catalyze biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, which form a system of scaffolding that maintains cell shape. Other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. Proteins are also necessary in animals' diets, since animals cannot synthesize all the amino acids they need and must obtain essential amino acids from food. Through the process ofdigestion, animals break down ingested protein into free amino acids that are then used in metabolism.
Proteins may be purified from other cellular components using a variety of techniques such as ultracentrifugation, precipitation, electrophoresis, andchromatography; the advent of genetic engineering has made possible a number of methods to facilitate purification. Methods commonly used to study protein structure and function include immunohistochemistry, site-directed mutagenesis, nuclear magnetic resonance and mass spectrometry.
Protein is a macro nutrient composed of amino acids that is necessary for the proper growth and function of the human body. While the body can manufacture several amino acids required for protein production, a set of essential amino acids needs to be obtained from animal and/or vegetable protein sources. Animal protein sources contain the complete set of essential amino acids, while all the essential amino acids can be obtained by eating a wide variety of plant foods. There is considerable debate over the amount of protein a person needs to consume per day, the current recommended daily intake (RDI) of protein is 46 grams for women aged 19-70 and 56 grams for men aged 19-70. Any excess protein consumed is turned into energy by the body, and it is controversial whether this excess protein causes a strain on the liver. A deficiency in protein leads to muscle atrophy, and impaired functioning of the human body in general. Below is a list of common foods with the highest protein to calorie ratio, for more information, see the sections on protein dense foods, other protein rich foods, low calorie high protein snacks, and protein isolates.
Chicken: Chicken Breast (58g) provides 17g protein. Chicken Leg (69g) provides 18g protein. Chicken Thigh (37g) provides 9g protein
Other fish high in protein per fillet(3oz or 85g): Tuna (22g), Salmon (22g), Halibut (22g), Snapper (22g), Perch(21g), Flounder and Sole (21g), Cod (20g),
Chicken: Chicken Breast (58g) provides 17g protein. Chicken Leg (69g) provides 18g protein. Chicken Thigh (37g) provides 9g protein
Other fish high in protein per fillet(3oz or 85g): Tuna (22g), Salmon (22g), Halibut (22g), Snapper (22g), Perch(21g), Flounder and Sole (21g), Cod (20g),
Other cheese high in protein per ounce(28g): Low-fat Cottage Cheese (5g), Low-fat Swiss Cheese (8g), Low-fat Cheddar (6g), Parmesan (10g), Romano (9g). *Low fat Mozzarella and Cottage cheese provide the most protein