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Structure of Antibody. Functions of Antibody IgG provides long term protection because it persists for months and years after the prescence of the antigen that has triggered their production.
IgG protect against bacteris, viruses, neutralise bacterial toxins, trigger compliment protein systems and bind antigens to enhance the effectiveness of phagocytosis. Main function of IgA is to bind antigens on microbes before they invade tissues. It aggregates the antigens and keeps them in the secretions so when the secretion is expelled, so is the antigen.
IgA are also first defense for mucosal surfaces such as the intestines, nose, and lungs. IgM enhance ingestions of cells by phagocytosis. IgE bind to mast cells and basophils wich participate in the immune response. This structure consists of two identical light L chain polypeptide of about Da and two identical heavy H chain of larger polypeptide of about Da or more.
Each light chain is bound to a heavy chain by a disulphide bond and by non-covelent interactions such as salt bride, hydrogen bonds and hydrophobic interaction to form a heterodimer H-L.
Similar non-covalent interaction and disulphide linkage link the two identical heterodimer H-L to each other to from basic structure of antibody ie.
Dimer of dimer. Anatomy of light L and heavy H chain: L- chain: L- chain of antibody is composed of about aminoacids. Around aminoacids are located at N-terminal amino-terminal and the aminoacids sequences varies among antibodies. This region of L-chain is known as variable V region. This variable region, composed of amino acids, give the antibody its specificity for binding antigen. The variable region includes the ends of the light and heavy chains. Treating the antibody with a protease can cleave this region, producing Fab or fragment antigen binding that include the variable ends of an antibody.
Material used for the studies shown below originated from Fab. The constant region determines the mechanism used to destroy antigen. The variable region is further subdivided into hypervariable HV and framework FR regions. Hypervariable regions have a high ratio of different amino acids in a given position, relative to the most common amino acid in that position. Four FR regions which have more stable amino acids sequences separate the HV regions.
The HV regions directly contact a portion of the antigen's surface. For this reason, HV regions are also sometimes referred to as complementarity determining regions, or CDRs. The FR regions form a beta-sheet structure which serves as a scaffold to hold the HV regions in position to contact antigen. This image represents the structure of an antibody's variable region Fab complexed with an antigen, in this case hen egg white lysozyme.
The other images in this section are derived from this structure.
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