Antibodies I Flashcards
1
Q
Proteins present in mucosal secretions, blood, & tissue fluid
A
Antibodies
2
Q
Bind to toxins, viruses, & bacteria, blocking their access to our cells
A
Antibodies
3
Q
Antibodies are classified as
A
Immunoglobins (Ig)
4
Q
The structure of all antibodies is based on a unit of
A
Four polypeptide chains
5
Q
Antibodies are made up of
A
2 heavy chains and 2 light chains
6
Q
Connect each heavy chain to its partner light chain, and connect the two heavy chains
A
Disulfide bonds
7
Q
In a given Ig, the two heavy chains are always identical, as are the
A
Two light chains
8
Q
Each Ig chain is divided into regions or domains consisting of around
A
110 amino acid residues
9
Q
How many domains are in the
- ) Light chain?
- ) Heavy chain?
A
- ) 2
2. ) 4
10
Q
The N-terminal domain on both the heavy and light chain are known as the
A
Variable domains (VL and VH)
11
Q
The other domains are called
A
Constant domains (CL and CH1-3)
12
Q
The heavy chain also contains a flexible
- in the middle
- allows the two arms of an Ig molecule to move with respect to eachother
A
Hinge domain
13
Q
The antigen-binding sites are formed in the
A
Variable domains
14
Q
Each Ig has two identical
A
Binding sites
15
Q
Antigens are often macromolecules. An antibody binds to only a small portion of an antigen’s surface, called an
A
Epitope or antigenic determinant
16
Q
Are both sterically and chemically complementary
A
Antibody and epitope
17
Q
Sterically they fit together the way a lock fits its key. The interacting surfaces form multiple
A
Noncovalent bonds
18
Q
A protein epitope typically contains 15-25 amino acid side chains, forming a ‘patch’ on the
A
Protein’s surface
19
Q
The number of weak interactions is in the range of 50-200. A small number of side chains on both sides contribute the bulk of the
A
Binding energy
20
Q
A small epitope, such as a short peptide or a small molecule, may interact with only a small portion of the
A
Combining site
21
Q
Combining sites are formed from only a small part of each
A
Variable domain
22
Q
Formed from complementarity-determining regions (CDR), loops of polypeptide chain at the ends of paired VH and VL domains
A
Combining site
23
Q
Each V domain has 3
A
CDRs
24
Q
The remainder of the V domains is largely B-sheet and comprises framework regions that hold
A
CDRs in place
25
When antibody V-domains are compared, CDR's are much more different than framework regions. For this reason, CDR’s are also called
Hypervariable regions
26
CDR’s of both VH and VL make up the combining site; they are held in place by interactions between them and between their associated
CH1 and CL domains
27
A large, complex, antigen such as a protein has many
Epitopes
28
When the immune system reacts to such an antigen, although each individual Ig molecule is epitope-specific, the population of antibodies produced in the immune system can bind to many different
Epitopes
29
Since each distinct type of antibody is produced by a clone of plasma cells, the process of antibody production in response to a complex antigen is termed a
Polyclonal response
30
Not all epitopes are equally strong stimuli. Most of the antibodies formed may be antibodies to a few
Immunodominant epitopes
31
Dominant epitopes are typically present in
Many copies
32
The structure of the binding site depends on the nature of the
Epitope
33
If the epitope is a small molecule the binding site will be a
Pit in the surface of the antibody
34
This "pit" is necessary because only by surrounding the small molecule can enough weak bonds be made to allow for
Good binding
35
If the epitope is elongate, such as a peptide or carbohydrate chain, the binding site will be a
Groove
36
If the epitope is part of the surface of a protein, the binding site will be a
Lumpy Surface
37
Cleave antibodies at specific sites
Proteases
38
Produces two Fab fragments and one Fc fragment
Papain Cleavage
39
Univalent antigen-binding fragments composed of one entire Ig light chain and the amino terminal part of one of the Ig heavy chain, linked to each other by a disulfide bond
Fab
40
Contains the variable region of the immunoglobulin molecule, which contains the antigen-binding site, and the first constant region
Fab
41
Crystallizable fragments composed of the carboxyterminal parts of the heavy chain constant regions of both Ig heavy chains linked to each other by disulfide bonds
Fc
42
Fc fragments are responsible for the effector functions of an
Immunoglobin
43
(Fab’)2 contains two Fab fragments, that is, it contains
2 light chains and portions of 2 heavy chains
44
(Fab’)2 contains two
Antigen combining sites
45
May be used when it is desired to bind antibody to antigen without cross-linking
Fab fragments
46
An Ig molecule consists of a heavy chain and a light chain. The light chain can be either a
Kappa or Gamma chain
47
Genes for the Ig chains are present in segments. Each gene segment has multiple copies which are clustered in a distinct chromosomal region in the
Germline cells
48
. For example, the Ig heavy chain gene complex consists of a constant (CH), a joint (JH), a diversity (D), and a variable (VH) region containing
11, 6, 25, and >130 gene segments, respectively
49
Ig genes are made
Somatically
50
During development of each antibodyproducing cell, its H- and Lchain genes are assembled from libraries of
Short gene segments
51
In an antibody-producing cell, after assembly, the gene for Ig k light chain contains exons encoding the
Variable domain and the constant domain
52
The V domain exon is composed of which two DNA segments?
V and J
53
A functional V-region exon was assembled by selection of one V and one J segment from each array during
B cell development
54
The unique structure of an antibody’s combining site, produced by choice of V, D, and J segments, and other mechanisms discussed below, defines its
Idiotype
55
The receptors by which T cells recognize antigens (TCR = T cell Receptor) resemble antibody
Fab regions
56
Each of the two chains of the TCR has a
Variable domain and a constant domain
57
The variable domain of the TCR a-chain of the receptor is assembled from
V and J segments
58
The variable region of the TCR B-chain is assembled from
V, J, and D segments
59
The splicing machinery requires that a pair of sites to be cut and spliced include one with a 12-base spacer and one with a 23-base spacer. This ensures the correct splicing of
V, D, and J segments
60
Because of the 12/23 requirement, a V segment cannot be spliced directly to a
J segment
61
Recognize the conserved DNA signals and target the initial cuts
RAG1 and RAG2 gene products
62
RAG stands for
Recombination of Antibody Genes
63
The RAG1/RAG2 complex has the structure of a bacterial
Transposase
64
RAG1 and RAG2 are found only in
Lymphocytes
65
Other proteins essential for splicing are found in all cells and form part of the DNA repair machinery. Hence some DNA-repair deficiencies also lead to
Immunodeficiency
66
Additional diversity is created at
Splice junctions
67
V/D and D/J splice joints occur in
CDR3 regions
68
Mechanisms that increase diversity at splice junctions increase combining-site diversity by a factor of about
10^5
69
Randomly adds nucleotides to the cut ends of V, D, and J segments
DNA terminal deoxyribonucleotidyl transferase (TdT)
70
Found only in developing lymphocytes and is sometimes used as a histochemical marker to identify them
TdT
71
Repeated exposure to antigen results in progressive increase in
Antibody affinity (called affinity maturation)
72
This is one reason why immunizations require a series of booster shots: each booster improves the
Affinity of the antibody
73
The basis of affinity maturation is that, in germinal centers, there is high-level somatic mutation of the
Variable regions of immunoglobulin genes
74
Mutation is random, so many mutations lower the affinity of the combining site for
Antigens
75
Cells with such mutations are no longer stimulated by antigen, and
Die
76
Cells with receptors which bind antigen the most tightly are most highly stimulated by it, proliferate most extensively, and occupy an increasing fraction of the
Population
77
Antibody gene rearrangements sometimes results in
Cancer
78
Rare errors in rearrangement can join the VDJ region of an immunoglobulin locus, not to a constant region segment, but to another gene entirely, sometimes on another chromosome. This may place this gene under the control of a powerful B-cell specific transcriptional enhancer close to the VDJ region. If the gene is involved in control of cell proliferation, overproduction may lead to uncontrolled cell division and formation of a clone of malignant cells. This is the origin of the chromosomal translocation seen in
Burkitt Lymphoma
79
The class (or isotype) of the antibody is defined by the
Heavy chain
80
Each class of antibody has a heavy chain with a different
Amino acid sequence
81
The five immunoglobulin classes are designated
IgA, IgG, IgM, IgE, and IgD
82
How many subclasses does
1. ) IgG have?
2. ) IgA have?
1. ) 4
| 2. ) 2
83
Subclasses have distinct functional roles; for example, IgG made in response to polysaccharide antigens is mostly
IgG2
84
There are two different kinds of light chain, designated
Kappa (k) and gamma (y)
85
An antibody-producing cell makes one and only one kind of
Light chain and heavy chain
86
Recognize only a single epitope
Monoclonal antibodies
87
Antibody-producing cells do not live long in culture. They are immortalized by fusing them with
Tumor Cells
88
Individual fused cells are then cloned and each clone must be screened for production of antibody to the desired
Antigen or epitope
89
Monoclonal antibodies are made in
Mice
90
DNA encoding the CDR’s of their V domains can be cloned and sequenced and then incorporated into human
H- and L-chain genes
91
Antibodies produced in this way are called
Humanized antibodies
92
By genetic engineering proteins can be produced that contain part of an
Antibody chain
93
For example, an experimental mode of anti-cancer therapy uses Fab fragments of an anti-tumor antibody to target a protein toxin to
Tumors
94
Makes only one type of light chain and one type of heavy chain (‘allelic exclusion’)
Each B lymphocyte
95
Successful assembly of one heavy-chain gene on one chromosome prevents rearrangement on the
Other
96
The appearance of these chains on the plasma membrane may create an intracellular signal that prevents further
Re-arrangement
97
Membrane and secreted forms of the same immunoglobulin are created by different patterns of
RNA splicing
98
B cells, prior to antigenic stimulation, make immunoglobulin as a
Transmembrane protein
99
In B cells, exons encoding the transmembrane and cytosolic domains of the Ig are retained when the primary transcript is spliced; in plasma cells they are
Excised
100
Antibodies of primary and secondary immune responses are
Different
