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Protein, broken down into amino acids, is seldom used as a main energy source except during starvation and glycolytic crisis (see bioenergetic systems). In humans, glycogen is made and stored primarily in the cells of the liver and skeletal muscle.
An O-linked glycoprotein has the sugar is bonded to an oxygen atom of a serine or threonine amino acid in the protein. [ 4 ] Glycoprotein size and composition can vary largely, with carbohydrate composition ranges from 1% to 70% of the total mass of the glycoprotein. [ 4 ]
Glycogen is a highly branched structure, consisting of the core protein Glycogenin, surrounded by branches of glucose units, linked together. [ 2 ] [ 12 ] The branching of glycogen increases its solubility, and allows for a higher number of glucose molecules to be accessible for breakdown at the same time. [ 2 ]
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 .
Small amounts of glycogen are found in the kidneys and even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy to nourish the embryo. [17] Glycogen is composed of a branched chain of glucose residues. It is primarily stored in the liver and muscles. [21]
Starch, cellulose, and glycogen ("animal starch") are common glucose polymers (polysaccharides). Some of these polymers (starch or glycogen) serve as energy stores, while others (cellulose and chitin, which is made from a derivative of glucose) have structural roles. Oligosaccharides of glucose combined with other sugars serve as important ...
M phase See mitosis. macromolecule Any very large molecule composed of dozens, hundreds, or thousands of covalently bonded atoms, especially one with biological significance. . Many important biomolecules, such as nucleic acids and proteins, are polymers consisting of a repeated series of smaller monomers; others such as lipids and carbohydrates may not be polymeric but are nevertheless large ...