On pages 144-145, Dr. Moalem discusses the immense diversity of the immune system. His discussion relates to Big Idea #3 (Living systems store, retrieve, transmit, and respond to information essential to life processes), as the millions of different antibodies are created by the immune system in response to the threats that come from viruses and other microbes.
First of all, how is it possible for these millions of unique antibodies to be created when there are only about 25,000 active, coding genes? Explain this process using Dr. Moalem's description of the V(D)J recombination mechanism. How is the V(D)J mechanism similar or different to the mechanism jumping genes use, and what are the overall evolutionary implications of these adaptable mechanisms? V(D)J is not the only process the immune system uses to react to different threats - research another mechanism that the immune system uses to combat threats, and discuss how that mechanism works.
(Posted by Matthew Zhang; mzhang4@students.d125.org)
While it is not completely understood why millions of unique antibodies can be created in human bodies when there are only around 25,000 active coding genes, there is a link that has been recently discovered between the behavior of jumping genes and the immune system's antibody production. On page 144, Dr. Sharon Moalem describes jumping genes as inserting or changing genetic material in brain cells during the early stages of brain development. Creating unique antibodies in the immune system is called V(D)J recombination. Just as we have learned in our current unit,(unit 11-immune system)B-cells are the basic building blocks to make antibodies in V(D)J recombination. B-cells first seek out instructions for a specific antibody in their DNA. Then, they snip away the lines of instructions for the other antibodies and sew the rest together to retain the instructions for the specific antibody it wants to create. However, these aren't the only mechanisms that utilize a cut-and-paste method. Scientists have been looking at the creation of receptors in lymphocyte cells. At the end of the creation, "the sequence is then cut and pasted together, and the excess bits of DNA discarded" (Science Daily).
ReplyDeleteThis mechanism of V(D)J recombination is similar to the mechanisms jumping genes use because jumping genes also use a cut-and-paste method. However, one key difference is that V(D)J recombination leaves a little loop when it reconnects the remaining strands. In contrast, jumping genes have a neat connection when they cut-and-paste. The overall evolutionary implications for jumping genes is it allows greater diversification within a population. By randomly cutting and pasting genetic material across the brain, brains are made unique in every individual. These changes can create favorable traits in some brains of the individuals of the population. So, these traits would be more likely to be passed on to offspring through natural selection can drive evolution in human brains. This follows Big Idea 1 (the process of evolution drives the diversity and unity of life). The evolutionary implications of the V(D)J mechanism is similar in that it could create favorable traits to be more likely to be passed on to offspring. Since the mechanism allows specific antibodies to be produced, if an individual has developed antibodies to a specific antigen, that can be passed on to offspring. This connects to what we are talking about in our current unit when mothers pass on antibodies for specific antigens through breastfeeding. By creating antibodies for antigens that can be very harmful to humans, the individuals will be more likely to pass it on to offspring and through natural selection evolution can be driven.
Another mechanism that the immune system uses to combat threats is the cell-mediated response. This is when a virus infects a cell. First, the macrophages arrive. The macrophages engulf the pathogen and the antigen is presented to helper T cells to find more infected cells. Then, the helper T cell proliferates, while secreting IL-2, and stimulates cytotoxic t cell is stimulated with the IL-2 and is activated. Afterwards, the antigen is presented to cytotoxic T cells. Once an infected cell is found, the cytotoxic T cell releases perforin, which causes pores in the cell membrane. The infected cell then finally lyses as a result of the pores forming.
(Tyler Hagen-thagen4@students.d125.org)