![]() ![]() Ĭut that creates a blunt end Many restriction enzymes make staggered cuts in the two DNA strands at their recognition site, which generates fragments with a single stranded "tail" that overhangs at both ends, called a sticky end. The modification enzyme adds a methyl group to one or two bases, and the presence of this methyl group prevents the restriction endonuclease from cutting the DNA. This is done by modifying the host DNA at or near each potential cleavage site. A restriction site is typically a palindromic sequence, which means that the restriction-site sequence is the same on each strand of DNA when read in the 5' to 3' direction.įor each restriction enzyme, bacteria also produce a modification enzyme so that a host bacterium's own DNA is protected from cleavage. Restriction Enzymes Restriction enzymes are endonucleases produced by bacteria that typically recognize small base pair sequences (called restriction sites) and then cleave both strands of DNA at this site. Two enzymes facilitate the production of such recombinant DNA molecules:ġ. Therefore, the long DNA molecules that compose an organism's genome must be cleaved into fragments that can be inserted into the vector DNA. Only relatively small DNA molecules can be cloned in any available vector. In order for DNA cloning to be completed, it is necessary to obtain discrete, small regions of an organism's DNA that constitute specific genes. Here, DNA fragmentation is a molecular genetic technique that permits researchers to use recombinant DNA technology to prepare large numbers of identical DNA molecules. This is a form of asexual reproduction where an organism splits into fragments and then each of these fragments develop into mature, fully grown individuals that are clones of the original organism (See reproductive fragmentation).ĭNA cloning can also be performed intentionally by laboratory researchers. However, problems within a cell can sometimes cause fragmentation that results in irregularities such as red blood cell fragmentation and sperm cell DNA fragmentation.ĭNA cloning can be performed spontaneously by the cell for reproductive purposes. These two ways in which fragmentation is used in cellular processes describe normal cellular functions and common laboratory procedures performed with cells. Apoptosis is the programmed destruction of cells, and the DNA molecules within them, and is a highly regulated process. DNA cloning is important in asexual reproduction or creation of identical DNA molecules, and can be performed spontaneously by the cell or intentionally by laboratory researchers. In cell biology, ways in which fragmentation is useful for a cell: DNA cloning and apoptosis. The consequence of antigen transfer from migratory DCs to lymph node DCs is not yet known, but we suggest that in the steady state, i.e., in the absence of stimuli for DC maturation, this transfer leads to peripheral tolerance of the T cell repertoire to self.For other uses, see Fragmentation (disambiguation). When we injected different I-E-bearing cells into C57BL/6 mice to look for a similar phenomenon in vivo, we found that short-lived migrating DCs could be processed by most of the recipient DCs in the lymph node. ![]() Quantitation of the amount of I-E protein in the B cell fragments revealed that phagocytosed I-E was 1-10 thousand times more efficient in generating MHC-peptide complexes than preprocessed I-E peptide. Antigen transfer was preceded by uptake orb cell fragments into MHC class II-rich compartments. Antigen transfer was also observed with human cells, where human histocompatibility leukocyte antigen (HLA)-DRα includes the same peptide sequence as mouse I-Eα. When immature DCs from I- A b mice were cultured for 5-20 h with activated I-E + B blasts, either necrotic or apoptotic, the DCs produced the epitope recognized by the Y-Ae monoclonal antibody and stimulated T cells reactive with the same MHC- peptide complex. This was monitored with the Y-Ae monoclonal antibody that is specific for complexes of I-A b MHC class II presenting a peptide derived from I-Eα. Here we describe how dendritic cells (DCs) process phagocytosed cell fragments onto major histocompatibility complex (MHC) class II products with unusual efficacy. Cells from the bone marrow can present peptides that are derived from tumors, transplants, and self-tissues. ![]()
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