An&nbsp;'''ology'''&nbsp;or&nbsp;'''[https://en.wikipedia.org/wiki/-logy -''logy'']'''&nbsp;is a scientific discipline.<br/> &nbsp; === Protein === '''Proteins'''&nbsp;are large&nbsp;[https://en.wikipedia.org/wiki/Biomolecule biomolecules]&nbsp;and&nbsp;[https://en.wikipedia.org/wiki/Macromolecule macromolecules]&nbsp;that comprise one or more long chains of&nbsp;[https://en.wikipedia.org/wiki/Amino_acid amino acid]&nbsp;[https://en.wikipedia.org/wiki/Residue_(biochemistry) residues]. Proteins perform a vast array of functions within organisms, including&nbsp;[https://en.wikipedia.org/wiki/Enzyme_catalysis catalysing metabolic reactions],&nbsp;[https://en.wikipedia.org/wiki/DNA_replication DNA replication],&nbsp;[https://en.wikipedia.org/wiki/Cell_signaling responding to stimuli], providing&nbsp;[https://en.wikipedia.org/wiki/Cytoskeleton structure to cells]&nbsp;and&nbsp;[https://en.wikipedia.org/wiki/Fibrous_protein organisms], and&nbsp;[https://en.wikipedia.org/wiki/Intracellular_transport transporting molecules]&nbsp;from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the&nbsp;[https://en.wikipedia.org/wiki/Nucleic_acid_sequence nucleotide sequence]&nbsp;of their&nbsp;[https://en.wikipedia.org/wiki/Gene genes], and which usually results in&nbsp;[https://en.wikipedia.org/wiki/Protein_folding protein folding]&nbsp;into a specific&nbsp;[https://en.wikipedia.org/wiki/Protein_structure 3D structure]&nbsp;that determines its activity. A linear chain of amino acid residues is called a&nbsp;[https://en.wikipedia.org/wiki/Polypeptide polypeptide]. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called&nbsp;[https://en.wikipedia.org/wiki/Peptide peptides]. The individual amino acid residues are bonded together by&nbsp;[https://en.wikipedia.org/wiki/Peptide_bond peptide bonds]&nbsp;and adjacent amino acid residues. The&nbsp;[https://en.wikipedia.org/wiki/Protein_primary_structure sequence]&nbsp;of amino acid residues in a protein is defined by the&nbsp;[https://en.wikipedia.org/wiki/DNA_sequencing sequence]&nbsp;of a gene, which is encoded in the&nbsp;[https://en.wikipedia.org/wiki/Genetic_code genetic code]. In general, the genetic code specifies 20 standard amino acids; but in certain organisms the genetic code can include&nbsp;[https://en.wikipedia.org/wiki/Selenocysteine selenocysteine]&nbsp;and—in certain&nbsp;[https://en.wikipedia.org/wiki/Archaea archaea]—[https://en.wikipedia.org/wiki/Pyrrolysine pyrrolysine]. Shortly after or even during synthesis, the residues in a protein are often chemically modified by&nbsp;[https://en.wikipedia.org/wiki/Post-translational_modification post-translational modification], which alters the physical and chemical properties, folding, stability, activity, and ultimately, the function of the proteins. Some proteins have non-peptide groups attached, which can be called&nbsp;[https://en.wikipedia.org/wiki/Prosthetic_group prosthetic groups]&nbsp;or&nbsp;[https://en.wikipedia.org/wiki/Cofactor_(biochemistry) cofactors]. Proteins can also work together to achieve a particular function, and they often associate to form stable&nbsp;[https://en.wikipedia.org/wiki/Protein_complex protein complexes]. Once formed, proteins only exist for a certain period and are then&nbsp;[https://en.wikipedia.org/wiki/Proteolysis#Protein_degradation degraded]&nbsp;and recycled by the cell's machinery through the process of&nbsp;[https://en.wikipedia.org/wiki/Protein_turnover protein turnover]. A protein's lifespan is measured in terms of its&nbsp;[https://en.wikipedia.org/wiki/Half-life half-life]&nbsp;and covers a wide range. They can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal or misfolded proteins are degraded more rapidly either due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as&nbsp;[https://en.wikipedia.org/wiki/Polysaccharide polysaccharides]&nbsp;and&nbsp;[https://en.wikipedia.org/wiki/Nucleic_acid nucleic acids], proteins are essential parts of organisms and participate in virtually every process within&nbsp;[https://en.wikipedia.org/wiki/Cell_(biology) cells]. Many proteins are&nbsp;[https://en.wikipedia.org/wiki/Enzyme enzymes]&nbsp;that&nbsp;[https://en.wikipedia.org/wiki/Catalysis catalyse]&nbsp;biochemical reactions and are vital to&nbsp;[https://en.wikipedia.org/wiki/Metabolism metabolism]. Proteins also have structural or mechanical functions, such as&nbsp;[https://en.wikipedia.org/wiki/Actin actin]&nbsp;and&nbsp;[https://en.wikipedia.org/wiki/Myosin myosin]&nbsp;in muscle and the proteins in the&nbsp;[https://en.wikipedia.org/wiki/Cytoskeleton cytoskeleton], which form a system of&nbsp;[https://en.wikipedia.org/wiki/Scaffolding scaffolding]&nbsp;that maintains cell shape. Other proteins are important in cell signaling,&nbsp;[https://en.wikipedia.org/wiki/Antibody immune responses],&nbsp;[https://en.wikipedia.org/wiki/Cell_adhesion cell adhesion], and the&nbsp;[https://en.wikipedia.org/wiki/Cell_cycle cell cycle]. In animals, proteins are needed in the&nbsp;[https://en.wikipedia.org/wiki/Diet_(nutrition) diet]&nbsp;to provide the&nbsp;[https://en.wikipedia.org/wiki/Essential_amino_acid essential amino acids]&nbsp;that cannot be&nbsp;[https://en.wikipedia.org/wiki/Amino_acid_synthesis synthesized].&nbsp;[https://en.wikipedia.org/wiki/Digestion Digestion]&nbsp;breaks the proteins down for metabolic use. Proteins may be&nbsp;[https://en.wikipedia.org/wiki/Protein_purification purified]&nbsp;from other cellular components using a variety of techniques such as&nbsp;[https://en.wikipedia.org/wiki/Ultracentrifugation ultracentrifugation],&nbsp;[https://en.wikipedia.org/wiki/Precipitation_(chemistry) precipitation],&nbsp;[https://en.wikipedia.org/wiki/Electrophoresis electrophoresis], and&nbsp;[https://en.wikipedia.org/wiki/Chromatography chromatography]; the advent of&nbsp;[https://en.wikipedia.org/wiki/Genetic_engineering genetic engineering]&nbsp;has made possible a number of methods to facilitate purification. Methods commonly used to study protein structure and function include&nbsp;[https://en.wikipedia.org/wiki/Immunohistochemistry immunohistochemistry],&nbsp;[https://en.wikipedia.org/wiki/Site-directed_mutagenesis site-directed mutagenesis],&nbsp;[https://en.wikipedia.org/wiki/X-ray_crystallography X-ray crystallography],&nbsp;[https://en.wikipedia.org/wiki/Nuclear_magnetic_resonance nuclear magnetic resonance]&nbsp;and&nbsp;[https://en.wikipedia.org/wiki/Mass_spectrometry mass spectrometry].<br/> <br/> <br/> <br/> <br/> &nbsp; <br/> <br/> &nbsp;[https://biolecture.org/Main_Page Main Page]&nbsp;»&nbsp;[https://biolecture.org/UNIST_Geromics_course UNIST Geromics course]&nbsp;»&nbsp;[https://biolecture.org/Geromics_Course_Students_Folder_2024 Geromics Course Students Folder 2024]&nbsp;»&nbsp;[https://biolecture.org/HyoungJinChoi_2024_Geromics_Course HyoungJinChoi 2024 Geromics Course]&nbsp;»&nbsp;[https://biolecture.org/Summary_class_Geromics_2024_HyoungJinChoi Summary class Geromics 2024 HyoungJinCho]