Home > Protein structure
Proteins are amino acid chains, made up from 20 different L-α-amino acids, also referred to as residues, that fold into unique 3-dimensional protein structures. The shape into a which a protein naturally folds is known as its native state, which is determined by its sequence of amino acids. Below about 40 residues the term peptide is frequently used. A certain number of residues is necessary to perform a particular biochemical function, and around 40-50 residues appears to be the lower limit for a functional domain size. Protein sizes range from this lower limit to several hundred residues in multi-functional proteins. Very large aggregates can be formed from protein subunits, for example many thousand actin molecules assemble into a an actin filament. Large protein complexes with RNA are found in the ribosome particles, which are in fact ' ribozymes'.
Biochemists refer to four distinct aspects of a protein's structure:
- Primary structure: the amino acid sequence
- Secondary structure: highly patterned sub-structures-- alpha helix and beta sheet--or segments of chain that assume no stable shapeA random coil is a polymer conformation where the monomers are arranged at random. Many simple polymers such as polyethylene inhibit only this conformation, more complex polymers with varying chemical groups attached to its backbone, such as proteins, sel. Secondary structures are locally defined, meaning that there can be many different secondary motifs present in one single protein molecule
- Tertiary structureIn biochemistry, the tertiary structure of a protein is its overall shape. All protein molecules are simple unbranched chains of amino acids, but it is by coiling into a specific three-dimensional shape that they are able to perform their biological funct: the overall shape of a single protein molecule; the spatial relationship of the secondary structural motifs to one another
- Quaternary structureIn biochemistry, many proteins are actually assemblies of more than one protein molecule, which in the context of the larger assemblage are known as protein subunits. In addition to the tertiary structure of the subunits, multiple-subunit proteins possess: the shape or structure that results from the union of more than one protein molecule, usually called subunit proteins subunits in this context, which function as part of the larger assembly or protein complexA protein complex is a group of two or more associated proteins. Protein complexes are a form of quaternary structure. Understanding the functional interactions of proteins is an important research focus in biochemistry, often referred to as proteomics..
In addition to these levels of structure, proteins may shift between several similar structures in performing of their biological function. In the context of these functional rearrangements, these tertiary or quaternary structures are usually referred to as " conformationIn chemistry, the conformation of a molecule is its spatial configuration. Examples of cyclohexane conformations: Chemistry.s," and transitions between them are called conformational changes.
The primary structure is held together by covalentCovalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons, by two atoms, in order to produce a mutual attraction, which holds the resultant molecule together. Atoms tend to share electrons in such a way peptide bondA peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (HO). This is a dehydration synthesis reaction, and usually occurs betws, which are made during the process of translationnucleus of the cell light blue , genes (DNA, dark blue are transcribed into RNA. This RNA is then subject to post-transcriptional modification and control, resulting in a mature mRNA red that is then transported out of the nucleus and into the cytoplasm p. The secondary structures are held together by hydrogen bonds. The tertiary structure is held together primarily by hydrophobic interactions but hydrogen bonds, ionic interactions, and disulfide bonds are usually involved too.
The two ends of the amino acid chain are referred to as the carboxy terminus (C-terminus) and the amino terminus (N-terminus) based on the nature of the free group on each extremity.
