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The incorporation of these nonstandard amino acids is rare. For example, 25 human proteins include selenocysteine in their primary structure, [64] and the structurally characterized enzymes (selenoenzymes) employ selenocysteine as the catalytic moiety in their active sites. [65] Pyrrolysine and selenocysteine are encoded via variant codons.
Proteins are polymer chains made of amino acids linked together by peptide bonds. During human digestion, proteins are broken down in the stomach to smaller polypeptide chains via hydrochloric acid and protease actions. This is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body. [3]
Fatty acylated proteins are proteins that have been post-translationally modified to include the covalent attachment of fatty acids at certain amino acid residues. [ 11 ] [ 12 ] The most common fatty acids that are covalently attached to the protein are the saturated myristic (14-carbon) acid and palmitic acid (16-carbon).
The side chains of the standard amino acids have a variety of chemical structures and properties, and it is the combined effect of all amino acids that determines its three-dimensional structure and chemical reactivity. [35] The amino acids in a polypeptide chain are linked by peptide bonds between amino and carboxyl
The most common macromolecules in biochemistry are biopolymers (nucleic acids, proteins, and carbohydrates) and large non-polymeric molecules such as lipids, nanogels and macrocycles. [1] Synthetic fibers and experimental materials such as carbon nanotubes [2] [3] are also examples of macromolecules.
Modified amino acids are sometimes observed in proteins; this is usually the result of enzymatic modification after translation (protein synthesis). For example, phosphorylation of serine by kinases and dephosphorylation by phosphatases is an important control mechanism in the cell cycle. Only two amino acids other than the standard twenty are ...
[6] [7] [8] Soluble fibre is marketed as serving a prebiotic function with claims for promoting "healthy" intestinal bacteria. [9] Bacterial metabolism of soluble fibre also produces short-chain fatty acids like butyric acid which may be absorbed into intestinal cells as a source of food energy. [6] [7] [8] cellulose; methyl cellulose ...
Metabolism (/ m ə ˈ t æ b ə l ɪ z ə m /, from Greek: μεταβολή metabolē, "change") is the set of life-sustaining chemical reactions in organisms.The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the conversion of food to building blocks of proteins, lipids, nucleic acids, and some carbohydrates; and the ...