Antibody Structure Flashcards
What class of proteins do antibodies belong to?
Glycoproteins
What is the basic structure?
Exist as monomers, dimers or pentamers of basic structure:
- 4 polypeptide chains with 2 identical light chains and 2 identical heavy chains
I.e. 2 pairs of 2 different proteins (Heavy chain and light chain)
What is structure of IgG?
Monomer - Y-shaped with 4 polypeptide chains
How is the antigen binding site formed? How many binding sites does IgG have?
N terminal end of one heavy chain and its neighbouring light chain cooperate to form an antigen binding site
IgG has 2 binding sites (as 2 identical of each chain) so a single molecule can bind 2 antigens
What is present at the N-terminal of light/heavy chains?
Variable region
What is present at the C-terminal of light/heavy chains?
Constant region
How are different binding sites with different specificities formed?
As it is the N-terminal parts (variable) or light/heavy chains that form binding sites so this creates huge diversity
What is the Fab region?
Antigen binding regions - binds to antigen on surface of microorganism
What is the specificity of antibody binding due to?
Folding of the Fab region
What is the Fc region?
Tail region which binds to Fc receptors on surface of immune system cells (macrophages). This allows antibodies to activate the immune system
This enhances phagocytosis as macrophages are activated
What are papain and pepsin?
Proteases
How does papain cut an IgG molecule?
Releases 2 arms of Y-shaped molecule, each with an antigen binding site (called a Fab fragment)
Releases stem of molecule, consisting of identical C-terminal parts of 2 H chains (called Fc fragment)
How does pepsin cut an IgG molecule?
With two arms still linked together - fragment has 2 binding sites
Antibodies can also bind to viruses. How is the useful?
Prevents them from entering cells and targets them for destruction
