PROTEIN STRUCTURE

=Protein Structure= '''Primary Structure - 1°''' [image:http://i.imgur.com/RA9DiSc.png?1] This is simply the sequence of amino acids. There are 20 different '''amino acids''' that can link together with peptide bonds in a vast number of different combinations. '''Secondary Structure - 2°''' [image:http://i.imgur.com/Vp7Nndq.png?1] The polypeptide chain then folds up in various ways. There are, however, two common patterns of folding. Most proteins will have sections that fold into a coiled '''α-helix''' and other sections that fold into a '''β-pleated sheet'''. These two patterns or motifs are extremely common and are often repeated throughout the protein. Secondary structures are maintained by the weak hydrogen bonds that form between chemical groups / side chains on each amino acid. '''Tertiary Structure - 3°''' [image:http://i.imgur.com/3xuLEcf.png?1] Every protein has a '''precise 3D structure''' formed by the folding of secondary structures into a complex shape called the tertiary structure. The tertiary structure is held together by links made between secondary structures. The strongest of these links are known as '''disulphide bridges''' (strong covalent bonds that form between neighbouring amino acids known as cysteine). '''Quaternary Structure - 4°''' [image:http://i.imgur.com/Uy7uSiL.png?1] Some complex proteins are comprised of more than one protein chain. Each polypeptide chain is referred to as a '''subunit'''. Haemoglobin (right) is comprised of 4 sub-units. Some proteins also have ''prosthetic groups'''; these are simply additional non-protein groups that help the protein to function. For example haem is an iron containing group that helps haemoglobin carry oxygen. '''So what is a Protein?''' Proteins are the working, moving parts of the cell, behind virtually all cellular processes. Proteins can move things around, break things apart, build things together, give the cell its shape and all its functions. Essentially a huge number of proteins working together are what cause everything in a cell to happen. Two of the main groups of proteins include; '''structural proteins''' –which give the cell structural support like the beams in a building; these give the cell its shape, and protein enzymes –these are the proteins that break down (catabolic) or piece together (anabolic) chemicals inside the cell.