Antigenic determinants bind to which of the following portions of an antibody?
A) Variable regions
B) Constant region
C) Only light chains
D) Only heavy chains

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Hint: The small site on an antigen to which a corresponding antibody may explicitly tie is termed an epitope or antigenic determinant. This is often generally one to 6 monosaccharides or five to eight amino acids build-up outside the antigen. Epitopes are divided into conformational epitopes and linear epitopes.

Complete answer:
> An epitope (antigenic determinant) is a component of an antigen recognized by the system (antibodies, B and T cells). Antigen processing occurs within the cell which further leads to fragmentation of proteins, and the expression of peptide -MHC molecules at the cell surface where they will be recognized by the T lymphocyte receptor on a T lymphocyte. Antigen processing is also done through either the endogenous pathway or through the exogenous pathway.
> Antibodies belong to the category of proteins called globulins. Collectively, antibodies are referred to as immunoglobulins (abbreviated Ig). All immunoglobulins have the identical basic molecular structure, consisting of 4 polypeptide chains. Two of the chains, which are identical in any given immunoglobulin molecule, are heavy (H) chains; the opposite two are identical light (L) chains. The terms heavy and lightweight simply mean larger and smaller. Each chain is manufactured separately and is encoded by different genes. The four chains are joined within the final immunoglobulin molecule to create a versatile Y shape, which is that the simplest form an antibody can take.
> At the tip of every arm of the Y-shaped molecule is a neighborhood called the antigen-binding, or antibody-combining, site, which is created by some of the heavy and light-weight chains. Every immunoglobulin molecule has a minimum of two of those sites, which are the image of each other. The antigen-binding site is what allows the antibody to acknowledge a selected part of the antigen (the epitope, or antigenic determinant).
> The heavy and light-weight chains that structure each arm of the antibody are composed of two regions, called constant (C) and variable (V). These regions are distinguished on the idea of organic compound similarity—that is, constant regions have essentially the identical organic compound sequence altogether antibody molecules of the identical class, but the amino alkanoic acid sequences of the variable regions differ quite a lot from antibody to antibody. This is sensible, because the variable regions determine the unique shape of the antibody-binding site. The tail of the molecule, which doesn't bind to antigens, consists entirely of the constant regions of heavy chains.
> The variable and constant regions of both the sunshine and also the heavy chains are structurally folded into functional units called domains. Each light chain consists of 1 variable domain (VL) and one constant domain (CL). Each heavy chain has one variable domain (VH) and three or four constant domains. Those domains that frame the “tail” of the essential Y-shaped molecule are answerable for the special biological properties of immunoglobulins—except, of course, for the capacity to bind to a selected antigenic determinant. The tail of the antibody determines the fate of the antigen once it becomes certain to the antibody.

Hence, the correct answer is option (A)

Note: The hinge region of the antibody may be a short stretch of amino acids on the heavy chain. It provides the molecule with flexibility, which is incredibly useful in binding antigens. This flexibility can actually improve the efficiency with which an antigen binds to the antibody. It also can help in cross-linking antigens into an outsized lattice of antigen-antibody complexes, which are easily identified and destroyed by macrophages.