Immunity-Chapter 4 Flashcards
True or False. The plasma membrane antibodies that function as antigen receptors of B lymphocytes can recognize a much broader range of chemical structures than the antigen receptors of T cells
True
Name the types of molecules that antigens for B lymphocytes recognize
Proteins, lipids, carbohydrates, nucleic acids, and small chemical groups
What types of molecules are recognized by the antigens of T cell receptors?
Peptides displayed on APCs bound to membrane proteins encoded in the major histocompatibility complex (MHC) genetic locus
Describe antigen receptor molecules
Antigen receptor molecules consists of regions(domains) involved in antigen recognition
What is the antigen recognizing domain called?
Variable 5 regions
What are the conserved portions of the antigen receptor called?
Constant (C) regions
What are CDRs?
Complementarity-determining regions in the V region where variability is concentrated within short stretches
What is BCR and TCR?
BCR- B cell receptorcomplex
TCR- T cell receptor `
How many forms do antibodies exist in?
2 forms
What are the differences between the 2 forms?
They are membrane bound antigen receptors on B cells or secreted proteins
TCRs exists only as membrane receptors
What is another name for antibodies?
immunoglobulin
Define antibody
An antibody is Y- shaped molecule that is composed 4 polypeptide chains including 2 identical heavy (H) and two identical light (L) chains with each chain containing a variable and a constant region.
Briefly describe the structure of the antibody
Made up of 4 chains; 2 heavy and 2 light chains. Each light chain is attached to a heavy chain and the heavy chains are attached to each other all by bisulfide bonds.
What is the make up of the light and heavy chains
Light chain- made up of 1 V and 1 C domain
Heavy chain- made up of 1 V and 3 or 4 C domains
Where does the antigen binding site?
The antigen binding site of the antibody is made up of the V regions of both heavy and light chains
Which forms of antigens are recognized by antibodies in B lymphocytes
Macromolecules such as proteins, polysaccharides, lipids, nucleic acids and small chemicals
What is antigen recognition mediated by in B cells?
Variable (V) regions of both heavy and light chains of membrane Ig
Signaling functions are mediated by what in B cells?
Proteins(Iga and Igb) associated with Ig
Effector functions are mediated by what?
Constant (C) regions of secreted Ig
In T cell receptor (TCR), what forms of antigens are recognized?
Peptides displayed by MHC molecules on APC
What form of peptides are recognized?
Linear peptides
In TCR, antigen recognition is mediated by what?
Variable (V) regions of a and b chains
In TCR, signaling functions are mediated by what?
Proteins (CD3 and zeta
In TCR, effector functions are mediated by what?
TCR does not perform effector functions
How many hypervariable regions does each heavy or light chain variable region has?
3 of which CDR3 has the most variability
Where is CDR3 located?
The junction of V and C regions.
What is special about the CDR3 region?
Because of its variability, the CDR3 portion of Ig molecule contributes most of antigen binding
What is the FAB?
The Fab(Fragment, Antigen, binding) region of Ig is the whole fragment of a light chain that contains both C and V domains. Each Ig molecule has 2 identical Fab regions binds antigens
What is Fc in Ig?
The heavy chain C domain make up Fc (Fragment, crystalline). This region tends to crystallize in solution. Each Ig molecule has 1 Fc region that is responsible for most of the biological activity and effector functions of the antibody.
Where is the hinge in an Ig molecule and what is its function?
Between the Fab and Fc regions of most Ig molecules. The hinge allows the 2 antigen-binding Fab regions of each antibody molecule to move independently of each other thus allowing and enabling them to simultaneously bind antigen epitopes that are separated from one another by varying distance
How is the Ig molecule anchored?
The C-terminal end of the heavy chain is anchored in the plasma membrane.
True or False. Light chains of Ig are attached to cell membranes.
False. Light chains are not attached to cell membranes.
How many types of light chains are there? Name them.
- kappa and Lamda. They differ in their C regions
True or False. A B cell can express both kappa and lamda.
False. A B cell can only express either kappa or lamda but never both
How many types of heavy chains are there? Name them
- mu, delta, gamma, epsilon, and alpha. They also differ in their C region.
True or False. Each type of light chain may complex with any type of heavy chain.
True
What are antibodies that have different heavy chains called?
Isotypes
True or False. Antibodies are named according to their heavy chains regardless of the light chain class.
True
True or False. The antigen receptors of naïve B lymphocytes that have not encountered antigen are membrane bound IgM and IgD.
True
Discuss the major classes of antibodies
5 classes
IgA found in mucosal immunity-body fluids-breast milk, tears, saliva
IgD- membrane bound- expressed with IgM
IgE-Monomer-on MAST cells-allergy-histamine-defense against helminthic or worm-like parasites
IgG-Monomer-Most common-Opsonization, complement activation, antibody depended cell-mediated cytotoxicity, feedback inhibition of B cells
IgM- Pentamer-Snow-like-First to appear during development or evolution, naïve B cell antigen receptor, complement activation
Define epitope
The parts of the antigen that are recognized by antibodies
