Question

Which of the following events does NOT generate diversity of antigen-binding specificities among the immunoglobulins?

a. H- and L-chain random combinations
b. Somatic Recombination
c. H-chain RNA alternative splicing
d. Somatic Hypermutation
e. Activation-Induced Cytidine Deaminase

Answer 1

H-chain RNA alternative splicing does not contribute to the diversity of antigen-binding specificities of immunoglobulins, unlike H- and L-chain combinations, somatic recombination, somatic hypermutation, and AID activity.

Step-by-step explanation:

The event that does NOT generate diversity of antigen-binding specificities among the immunoglobulins is c. H-chain RNA alternative splicing. The diversity of antibodies is mainly due to several mechanisms: a. H- and L-chain random combinations, which are the association of different heavy (H) and light (L) chains; b. Somatic Recombination, where V, D, and J segments of the DNA rearrange to create a unique antibody variable region; and d. Somatic Hypermutation, where mutations are introduced in the variable regions to refine antigen specificity.

e. Activation-Induced Cytidine Deaminase (AID) also contributes to diversity by initiating somatic hypermutation and class-switch recombination. However, H-chain RNA alternative splicing is not known to contribute to the diversity of antigen-binding specificities of immunoglobulins.

Answer 2

H-chain RNA alternative splicing does not contribute to the diversity of antibody antigen-binding sites. Instead, diversity arises from somatic recombination, somatic hypermutation, and various gene rearrangements that result in a vast repertoire of unique antibodies for the immune system.D is the correct option.

Step-by-step explanation:

The event that does NOT generate diversity of antigen-binding specificities among the immunoglobulins is option c: H-chain RNA alternative splicing. This process refers to the variations that can occur within a gene at the level of RNA editing, which can result in different protein isoforms from a single gene; however, it does not contribute to the diversity of antigen-binding sites. The diversity of these sites is largely attributed to processes such as random combinations of heavy (H) and light (L) chains, somatic recombination, somatic hypermutation, and activity from enzymes like Activation-Induced Cytidine Deaminase (AID). These mechanisms allow for a vast array of unique antibodies capable of targeting an immense variety of antigens.

Processes such as V, D, J segment rearrangements and mRNA splicing contribute substantially to creating a diverse array of immunoglobulin molecules with unique antigen-binding sites. For example, through the random excision of V, J, and sometimes D segments of DNA by DNA recombinase, as well as splicing at the mRNA level, a single germ-line B cell can give rise to a multitude of unique antibodies. This is because each differentiated B cell will have a unique set of VJ (or VDJ) combinations leading to millions of specificities within an individual's immune system.

Genetic rearrangements and the involvement of AID in somatic hypermutation further diversify the repertoire of antibodies that can bind to different antigens, thus bolstering the efficiency and effectiveness of the human immune system. It is these genetic mechanisms that enable humans to produce more than 1012 different antibody molecules, despite having less than 50,000 genes in the genome.