Transmembrane proteins contain alpha-helices with specific hydrophobic properties allowing them to traverse membranes and be stable within the cell membrane. Fingernails and toenails are also made up of alpha-helices. Some fibrous proteins, including alpha-keratin, are almost completely comprised of alpha-helices. Many globular proteins have multiple alpha-helical portions separated by long stretches of non-helical regions. The alpha-helix is a right-handed helical coil that is held together by hydrogen bonding between every fourth amino acid. Two folds that are extremely common in biochemistry are the alpha-helix and the beta-pleated sheet. Many of these coils and folds repeat so often that they have been given names.

Most proteins have segments of their polypeptide chains that are either coiled or folded in patterns that contribute to the protein’s shape. It is significant to point out that the only hydrogen bonds involved in secondary structure do not include any involving amino acid side chains. The hydrogen bonds form between the partially negative oxygen atom and the partially positive nitrogen atom. The secondary structure arises from the hydrogen bonds formed between atoms of the polypeptide backbone. Quaternary structure is the association between two or more polypeptides, but not every protein has a quaternary structure. Tertiary structure is the three-dimensional shape of the protein determined by regions stabilized by interactions between the side chains. Secondary structure is comprised of regions stabilized by hydrogen bonds between atoms in the polypeptide backbone. In brief, primary structure is the linear chain of amino acids. Įvery protein can be described according to its primary structure, secondary structure, tertiary structure, and quaternary structure. By forming peptide bonds between the amino and carboxyl groups on two different amino acids, large polypeptide chains can be created. As diverse as they can be, they are all made up of the same 20 amino acids. They are known as the most structurally complicated biological molecules. Each of these proteins has its own structure and function. Humans have tens of thousands of proteins in their bodies at any given moment in time. Different proteins can play a role in speeding up chemical reactions, storage, defense, cell communication, movement, and structural support. There are many different types of proteins. They account for 50% of the dry mass of cells and play a role in everything an organism does. Nearly every function in living beings depends on proteins.

Secondary structure of protein download