The immunoglobulin bound to the B lymphocytes is the receptor of the
B lymphocyte (BCR). It is also an existing form of the antibody, so the BCR
have the light chain and the heavy chain.
What is the machinery of the formation of the antibody? It is due to the rearrangement of the gene. There are two types of chains in the antibody, and the formation of each other is different. In the formation of the light chain, V gene segment (variable, V) and J gene segment (Joining, J) first join together, becoming the V-J. Then the V-region (V-J) is close to the C-region, but there is also a short intron between the V and C. After transcription, under the RNA splicing, the mRNA get rid of the intron between V and L (leader segment, which can direct the protein into the cell’s secretory pathways), and the intron between V and C, and the mRNA can be translated. As for the heavy chain, there is a diversity segment (D) between the V and J. The D and J joins together first, then it is similar to the formation of the light chain. But, what is different is that the C-region has a lot of exons, between each exon there is an intron, and one of the exons can become a hinge region after it translated, for it can form the disulfide bonds.
How can the DNA rearrangement be regulated? There is a RSS (Recombination signal sequence) adjacent to the functional segment. RSS includes three parts, a heptamer (conversed,-5’CACAGTG3’-), a spacer (either 12 or 23 base pairs) and a nonamer (conversed,-5’ACAAAAACC3’-). With the 12/23 rule, the V and J(or V, D and J can join to each other orderly).
When the joining segments are in the same orientation, the signal joint is in a circular piece of extrachromosomal DNA, which is lost from the genome when the cell divides. While in the opposite orientation, alignment of the RSSs requires the coiled topology, rather than a simple loop like the former, so that joining the ends of the two heptamer sequences results in the inversion and integration of intervening DNA into a new position on the chromosome. Again, the joining of the V and J segments creates a functional V-region exon. There are lots of enzymes play roles in the joining, like RAG1/2, Ku70/80 etc. Normal 0 7.8 磅 0 2 false false false EN-US ZH-CN X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:普通表格; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.5pt; mso-bidi-font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-font-kerning:1.0pt;}
What is the machinery of the formation of the antibody? It is due to the rearrangement of the gene. There are two types of chains in the antibody, and the formation of each other is different. In the formation of the light chain, V gene segment (variable, V) and J gene segment (Joining, J) first join together, becoming the V-J. Then the V-region (V-J) is close to the C-region, but there is also a short intron between the V and C. After transcription, under the RNA splicing, the mRNA get rid of the intron between V and L (leader segment, which can direct the protein into the cell’s secretory pathways), and the intron between V and C, and the mRNA can be translated. As for the heavy chain, there is a diversity segment (D) between the V and J. The D and J joins together first, then it is similar to the formation of the light chain. But, what is different is that the C-region has a lot of exons, between each exon there is an intron, and one of the exons can become a hinge region after it translated, for it can form the disulfide bonds.
How can the DNA rearrangement be regulated? There is a RSS (Recombination signal sequence) adjacent to the functional segment. RSS includes three parts, a heptamer (conversed,-5’CACAGTG3’-), a spacer (either 12 or 23 base pairs) and a nonamer (conversed,-5’ACAAAAACC3’-). With the 12/23 rule, the V and J(or V, D and J can join to each other orderly).
When the joining segments are in the same orientation, the signal joint is in a circular piece of extrachromosomal DNA, which is lost from the genome when the cell divides. While in the opposite orientation, alignment of the RSSs requires the coiled topology, rather than a simple loop like the former, so that joining the ends of the two heptamer sequences results in the inversion and integration of intervening DNA into a new position on the chromosome. Again, the joining of the V and J segments creates a functional V-region exon. There are lots of enzymes play roles in the joining, like RAG1/2, Ku70/80 etc. Normal 0 7.8 磅 0 2 false false false EN-US ZH-CN X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:普通表格; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.5pt; mso-bidi-font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-font-kerning:1.0pt;}
