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receptor
chemistry specific cell binding site or molecule: a molecule, group, or site that is in a cell or on a cell surface and binds with a specific molecule, antigen, hormone, or antibody

receptor
In biochemistry, receptors are special structures that can be found in cells. Receptors bind (attach) to specialised molecules. If the receptor has this type of molecule, it is activated, but if it doesn’t it is deactivated. Depending on its state, a change inside the cell may happen.

In short, receptors work like locks and keys. With the key, the lock can be locked or unlocked. If it is unlocked, the door belonging to it can be opened.

Receptors are proteins embedded in the cell membrane. They are proteins that bind to specific signal molecules, which enables the cell to respond to the signal molecule.

Receptor proteins can affect the cell in three main ways:

1. Receptor proteins can change the permeability of the cell membrane. The cell may be coupled with an ion channel, and the binding of the protein to a signal molecule can cause the ion channel to open. This allows specific ions to cross the cell membrane. This type of receptor protein is very important to the nervous system.

2. Receptor proteins can cause the formation of a second messenger. A second messenger is a sort of signal molecule in the cytoplasm- it amplifies the message of the first signal molecule. Second messengers can activate enzymes or open ion channels in the cell membrane.

3. Receptor proteins, when binded to a signal molecule, can act as an enzyme (a biological catalyst that speeds up a chemical reaction). The protein can also activate other enzymes in the cell or cell membrane.

antigen
When an antigen is introduced into the body it causes the production of antibodies. Antigens can include bacteria, cells of transplanted organs, and toxins. Strictly speaking, an antigen is any substance that can stimulate the production of antibodies and combine specifically with them. ‘

An antigen defined as any molecule that binds specifically to an antibody, the term now also refers to any molecule or molecular fragment that can be bound by a major histocompatibility complex (MHC) and presented to a T-cell receptor[3]. “Self” antigens are usually tolerated by the immune system; whereas “Non-self” antigens are identified as intruders and attacked by the immune system. Autoimmune disorders arise from the immune system reacting to its own antigens.

tigens are usually proteins or polysaccharides. This includes parts (coats, capsules, cell walls, flagella, fimbrae, and toxins) of bacteria, viruses, and other microorganisms

An antigen is any large molecule or organism which triggers a specific (rather than generalised) immune response against itself within the host body. When the body detects an antigen, the adaptive immune system produces B & T lymphocytes with antigen receptors on their surface of specific shape to bind with, and destroy that antigen; the process takes a few days, but once made, antigen receptors for that pathogen remain in the body ready to mount a much faster attack should the same antigen be encountered in the future.
Some antigens only trigger a response in some people – for instance, pollen causes hayfever (which is an immune response) in some people, but not in others; in autoimmune disorders, the body mistakes normal body cells for antigens, and attacks them in – in multiple sclerosis, myelin is seen as an antigen, and is destroyed.

In vaccinations, dead or weakened antigens are introduced into the body, which then produces lymphocytes to deal with it & any future invasions by that antigen, giving the person immunity.

Antibodies
are special proteins , The immune system uses antibodies to identify foreign objects, such as bacteria and viruses. These objects are then neutralized, so that they can no longer cause problems and diseases.

Each antibody is different. They are all designed to attack only one kind of virus or bacteria. For instance, an antibody designed to destroy smallpox are unable to hit the Bubonic plauge or the common cold. An antibody resembles the letter “Y”. At the two ends of the “Y” are specially shaped antigens that can only insert themselves in one type of germ. This is needed, because every antibody is different. When the antibody finds the germ it’s after, it “knows” because of its special antigen

Antibody a protein made by plasma cells (a type of white blood cell) in response to an antigen (a substance that causes the body to make a specific immune response). Each antibody can bind to only one specific antigen. The purpose of this binding is to help destroy the antigen. Some antibodies destroy antigens directly. Others make it easier for white blood cells to destroy the antigen.
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Antibodies are proteins in our blood that are designed to bind to specific proteins that
Yes but how does the binding or lock and key work. Also what is CD identifier ?