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ProteinA protein (from the Greek protas meaning "of primary importance") is a complex, high-molecular-mass, organic compound that consists of amino acids joined by peptide bonds. Proteins are essential to the structure and function of all living cells and viruses. Different proteins perform a wide variety of biological functions. Some proteins are enzymes, which catalyze chemical reactions. Other proteins play structural or mechanical roles, such as those that form the struts and joints of the cytoskeleton, which is like a system of scaffolding within a cell. Still more functions filled by proteins include immune response and the storage and transport of various ligands. Proteins are a class of bio-macromolecules, alongside polysaccharides, lipids, and nucleic acids, that make up the primary constituents of biological organisms. Proteins are essentially polymers made up of a specific sequence of amino acids. The details of this sequence are stored in the code of a gene. Through the processes of transcription and translation, a cell reads the genetic information and uses it to construct the protein. In many cases, the resulting protein is then chemically altered (post-translational modification), before becoming functional. It is very common for proteins to work together to achieve a particular function, and often physically associate with one another to form a complex. In nutrition, proteins are broken down through digestion back into free amino acids for the organism, including those the organism may not be able to synthesize itself. Proteins are among the most actively-studied molecules in biochemistry, and were discovered by Jöns Jakob Berzelius in 1838. Proteins are polymers built from 20 different L-alpha-amino acids. Proteins are assembled from amino acids using information present in genes. Genes are transcribed into RNA, RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA that undergoes translation into a protein. mRNA is translated by ribosomes that match the three-base codons of the mRNA to the three-base anti-codons of the appropriate tRNA. The enzyme aminoacyl tRNA synthetase catalyzes the addition of the correct amino acid to their tRNAs. The two ends of the amino acid chain are referred to as the carboxy terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the functional group on each extremity. Proteins fold into unique 3-dimensional structures. The shape into which a protein naturally folds is known as its native state, which is determined by its sequence of amino acids. Thus, proteins are their own polymers, with amino acids being the monomers. Biochemists refer to four distinct aspects of a protein's structure: Primary structure: the amino acid sequence Secondary structure: highly patterned sub-structures — alpha helix and beta sheet — or segments of chain that assume no stable shape and are formed by hydrogen bonding. Secondary structures are defined, meaning that there can be many different secondary motifs present in one single protein molecule. Tertiary structure: the overall shape of a single protein molecule; the spatial relationship of the secondary structural motifs to one another; primarily formed by hydrophobic interactions, but hydrogen bonds, ionic interactions, and disulfide bonds are usually involved too. Quaternary structure: the shape or structure that results from the union of more than one protein molecule, usually called protein subunits in this context, which function as part of the larger assembly or protein complex. Check out the following recipes that are tagged "Protein":
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