Molecular Biology


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Question 1

According to Clark (2005), the role played by B cells in the humoral immune system cannot be understated. In most mammals, the production of B cells (immature) takes place in the bone marrow. It is from here that they migrate to the spleen on attaining the IgM+ immature stage. The development of the B cells is informed by a number of stages. It is important to note that each stage concerns itself with a genome content change. The stages informing the development of the B cells include the Progenitor stage, the early pro stage, the late pro stage, the Pre-B cells (large) stage, the pre-B cells (small) stage, the immature B cells stage and finally the mature B cells stage.

Question 2

When it comes to the development and maturation of the T cell, it is important t first note that the bone marrow haematopoietic stem cells constitute the origin of the T cells. Immature thymocytes which are essentially in large proportions come about as a result of cell division and though they later die in large numbers (about 98% of the total) as they develop, the remaining ones constitute that T cells (immunocompetent) after exiting the thalamus. It is important to note that when it comes to maturation, selection (both positive as well as negative) informs the death T cells in their development stage.

Question 3

Developing B cells must be able to produce a functional m chain before it is allowed to continue development as there is an existing need to come up with a variable domain in each individual B cells immunoglobin.  According to Clark (2005), the antibody loci genome content change informs the various changes of the B cell development process. It is important to note that two heavy (H) chains that are identical and the two light (L) chains which are also identical make up the antibody. The C (Constant) region and the V (variable region) house the gene specifying the two heavy (H) chains that are identical and the two light (L) chains which are also identical.

Question 4

Allelic exclusion is largely important and relevant as it underlines or highlights the B cells monospecificity. Over time, Allelic exclusion has been subjected to much detailed observation as well as analysis as far as cell surface receptor genes are concerned as well as the B lymphocytes immune cells.  As far as the occurrence of Allelic exclusion in B and T cell development is concerned, a single gene allele ends up being expressed triggering the silencing of the other allele.

Question 5

In regard to their development of B cells and T cells, RAG 1 and RAG 2 help in receptor editing. This is a process involving the B receptor cell light chain gene rearrangement. This is important as there is a need to ensure that the receptor cell produces a mire auto-reactive BCR. Clark (2005) notes that apoptosis is often preceded by a less auto reactive BCR. It can also be noted that severe combined immunodeficiency or what is largely known as SCID comes about as a result of RAG 1 and RAG 2 gene defects and hence the absence of the same may inform adverse results as far as cell proliferation is concerned.

Question 6

When it comes to the B cell development, Pax5 is important as far as the B-lineage committed precursor cells differentiation is concerned. However, it may also be noted that just like in the case of Notch 1 in T cell development, the role played by Pax 5 is largely dual. This includes the B lineage specific cells activation as well as the inappropriate B lineage repression. When it comes to Notch 1 in T cell development, it is important to note that in a majority of developmental systems, they influence the decisions in regard to cell-fate. Notch 1 also goes a long way to avert the development of αβ T cells as opposed to γδ T cells and hence it follows that an enhanced activity of notch has an effect on γδ T cells.

Question 7

The recognition of MHC molecules by the T cells is significant as knowing the processed form of their cognate antigen as availed by the antigen presenting cells MCH is critical to the adaptation of the T cell receptor. This essentially informs the activation of the macrophage in such a way that T cells can receive multiple signals that are important when it comes to the recognition of the presented peptide. Eliminating this crucial test cannot hence make it difficult for T cells to identify their processed form of cognate antigen. However, it can be noted that when it comes tio γδ T cells, there is no restriction whatsoever in regard to MHCs and protein recognition.

Question 8

As a specialized otr5gan, the thylamus plays a critical role as far as the education of the T cells is concerned. When it comes to the development of thymocyte, the earliest events occur at the cortex. It is also at the cortex that the rearrangement of genes as well as selection (positive) of the T cell receptor cells takes place. By the time of reaching the medulla, Thymocytes usually pass through a number of gene rearrangements in regard to T receptor cells and with this comes the exposition to negative selection though the degree of exposition in this case is fairly limited.

Question 9

The development processes in a T cell that inform its MHC restriction as well as requirement for tolerance of self include the progenitor B cells process, the late pro B Cells process as well as the Small Pre B cells process. When it comes to the progenitor B cells process, the heavy chain is germ line and so is the light chain. the late pro B Cells process heavy chain I this case undergoes rearrangement (V-DJ) but it remains germ line when it comes to the light chain. Lastly, the Small Pre B cells process has a heavy chain that is rearranged (VDJ) and when it comes to the light chain, the rearrangement is VJ.

Question 10

For purposes of tolerance once the T cells leave the thymus, the T cell receptor enhances the ability of T cells to identify antigens that are foreign. Therefore, during the thymocyte maturation, there are a number of genetic rearrangements that happen in the T receptor and in the end, a T cell receptor is contained within each and every T cell. It shall be noted that the genetic rearrangements in this case that seem random, are critical towards the enhancement of mechanisms concerned with central tolerance.


Clark, D.P. (2005). Molecular biology. Academic Press


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