Note the R groups of the amino acids in the beta sheet point out at a right angle to the hydrogen bonds holding the beta sheets together and not involved in the hydrogen bonds that maintain the structure. either running in same or opposite direction). Beta sheets are often denoted as parallel arrows (see image) identifying the direction the sequence runs, as beta sheets can both be parallel or anti parallel depending on how the N- and C-termini align (i.e. This allows hydrogen bonds to form between carbonyl and amino groups of the parallel linear chains, therefore forming the beta sheets. Beta sheetsīeta sheets (sometimes described as beta pleated sheets) are formed when the linear chains fold back on themselves leaving the chains to run parallel to each other. Note the R groups of the amino acids point out from the α-helix and are not involved in the hydrogen bonds that maintain the structure. This along with the fact all natural amino acids are in the form of 1 enantiomer* leads to the right handed helical structure forming (* with the exception of glycine which is not chiral). The alpha-helix structure is in the form of a right handed coil and is formed through hydrogen bonding between the carbonyl group and amino group of every 3.6 amino acids. It should be noted that a single secondary structure rarely extends throughout the peptide chain, it usually just forms a section within the chain. There are two main secondary structures that occur, both of which are governed by hydrogen bonding between carbonyl and amino groups of the amino acids in the peptide chain. The secondary protein structure describes the first step in how the amino acid sequence starts to fold in three dimensional space. Although the primary structure maybe simple, it is key in determining how the protein folds as it is the interactions between amino acids that govern subsequent folding. The primary protein structure is the simplest way to describe a protein, and is simply the linear sequence of amino acids that makes up the peptide chain. Download a printable version of this document here.Ī proteins three dimensional structure is complex, however it can be broken down to allow a greater understanding of how a protein folds into its complex three dimensional structure.
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