Proteins and the Urea Cycle By Bhoomika Sharma
What are proteins? any of a class of nitrogenous organic compounds which have large molecules composed of one or more long chains of amino acids and are an essential part of all living organisms, especially as structural components of body tissues such as muscle, hair, etc., and as enzymes and antibodies. Primary structure Primary structure
Types of Proteins The structure of proteins is basically categorised in 4 types: Primary Structure Secondary Structure - Tertiary Structure Quaternary Structure
Primary Structure The primary structure of a protein refers to the linear sequence of amino acids in the polypeptide chain. The primary structure is held together by covalent bonds such as peptide bonds, which are made during the process of protein biosynthesis. The two ends of the polypeptide chain are referred to as the carboxyl terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the free group on each extremity
Secondary Structure Secondary structure refers to highly regular local sub-structures on the actual polypeptide backbone chain. Two main types of secondary structure, the a-helix and the -strand or -sheets, were suggested in 1 951 by Linus Pauling and coworkers. These secondary structures are defined by patterns of hydrogen bonds between the main-chain peptide groups Alpha Helix Beta Sheets
Tertiary Structure Tertiary structure refers to the three-dimensional structure of monomeric and multimeric protein molecules. The -helixes and -pleated-sheets are folded into a compact globular structure. The folding is driven by the non-specific hydrophobic interactions, the burial of hydrophobic residues from water, but the structure is stable only when the parts of a protein domain are locked into place by specific tertiary interactions, such as salt bridges, hydrogen bonds, and the tight packing of side chains and disulfide bonds. The disulfide bonds are extremely rare in cytosolic proteins, since the cytosol (intracellular fluid) is generally a reducing environment.
Pleated sheet Primary protein structure Tertiory protein structuro occurs wtan certain atractcns are present betroon apha helcos and ploated cheets quence of a canofaniro acids Amino Acids Alpha helix Pleated sheet Alpha helx Secondary protein structure ocors when tra sequence at arrano soda are tinked by hydrogen bonds Quaternary protein structure o proten condiating of more than ono amino bcid chain
Quaternary Structure Quaternary structure is the three-dimensional structure of a multi-subunit protein and how the subunits fit together. In this context, the quaternary structure is stabilized by the same non- covalent interactions and disulfide bonds as the tertiary structure. Complexes of two or more polypeptides (i.e. multiple subunits) are called multimers. Specifically it would be called a dimer if it contains two subunits, a trimer if it contains three subunits, a tetramer if it contains four subunits, and a pentamer if it contains five subunits. Multimers made up of identical subunits are referred to with a prefix of "homo-" (e.g. a homotetramer)and those made up of different subunits are referred to with a prefix of "hetero-", for example, a heterotetramer, such as the two alpha and two beta chains of hemoglobin.