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Protein is a nutrient needed by the human body for growth and maintenance. Aside from water, proteins are the most abundant kind of molecules in the body. Protein can be found in all cells of the body and is the major structural component of all cells in the body, especially muscle. This also includes body organs, hair and skin.
The mechanical properties of proteins are highly diverse and are often central to their biological function, as in the case of proteins like keratin and collagen. [110] For instance, the ability of muscle tissue to continually expand and contract is directly tied to the elastic properties of their underlying protein makeup.
At the top level are all alpha proteins (domains consisting of alpha helices), all beta proteins (domains consisting of beta sheets), and mixed alpha helix/beta sheet proteins. While most proteins adopt a single stable fold, a few proteins can rapidly interconvert between one or more folds. These are referred to as metamorphic proteins. [5]
Proteins can have structural and/or functional roles. For instance, movements of the proteins actin and myosin ultimately are responsible for the contraction of skeletal muscle. One property many proteins have is that they specifically bind to a certain molecule or class of molecules—they may be extremely selective in what they bind.
Fibrous proteins are structural or storage proteins that are typically inert and water-insoluble. A fibrous protein occurs as an aggregate due to hydrophobic side chains that protrude from the molecule. A fibrous protein's peptide sequence often has limited residues with repeats; these can form unusual secondary structures, such as a collagen ...
Heat shock proteins (HSPs) are a family of proteins produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock , [ 1 ] but are now known to also be expressed during other stresses including exposure to cold, [ 2 ] UV light [ 3 ] and during wound healing or tissue remodeling. [ 4 ]
Looking from the bottom up there are ~20,000 protein coding genes in the human genome, (of which it is estimated that 12,733 already have Wikipedia articles (the Gene Wiki) about them). If one were to include splice variants, some argue that there could be as many as 500,000 unique human proteins, of which only about 900 are listed here.
Used in proteins and as a storage for ammonia, it is the most abundant amino acid in the body. Arginine: R Arg Functionally similar to lysine. Serine: S Ser Serine and threonine have a short group ended with a hydroxyl group. Its hydrogen is easy to remove, so serine and threonine often act as hydrogen donors in enzymes.