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DNA Structure, Sequencing, Synthesis, and Modification: Making Biology Molecular
Published in Richard J. Sundberg, The Chemical Century, 2017
Restriction endonucleases are a key tool for manipulation of DNA. They are enzymes that can cleave DNA at particular sequences of 4–8 base pairs. They were first discovered and their importance recognized by Hamilton Smith, Daniel Nathan, and Werner Arber, who received the 1978 Nobel Prize in Physiology or Medicine.i Dozens of such enzymes have been isolated and characterized. Because the cleavage occurs at specific sites, the sequence at the cleavage site is known. Furthermore, other DNA cleaved by the same endonuclease will terminate in the same matching sequence. The cleavage often occurs with a short overhang on each strand. These termination sites are called “sticky,” that is they can base-pair to another matching segment. If the enzyme is used to cleave both the DNA to be inserted and the host DNA, the sequences will attach by hydrogen bonding. In the presence of a DNA ligase, the ends will become attached and incorporated into the original cleaved strand.
Synthetic Biology and Artificial Intelligence
Published in Lavanya Sharma, Mukesh Carpenter, Computer Vision and Internet of Things, 2022
The CRISPR/Cas9 gene-editing system constrains two essential constituents: small guided RNA (gRNA) and Cas9 endonuclease. gRNA is a chimerical RNA molecule constituted from tracrRNA (trans-activating CRISPR RNA) and crRNA, where crRNA is a part of RNA that contains the gRNA locating in the specific part of host DNA linking to tracrRNA. It manages the Cas9 protein to the genome TS. Therefore, selecting a target location with pronounced targeted activation and low non-target locations is essential for gene editing. The activation of CRISPR-Cas9 during gene editing in mammalian cells is induced by numerous factors, like its secondary structure and availability of chromatin-guided sequence [85–88].
Why Human Germline Editing is More Problematic than Selecting Between Embryos: Ethically Considering Intergenerational Relationships
Published in The New Bioethics, 2018
The technology of purposeful DNA modification has advanced rapidly in the last few years with the development of RNA-guided endonucleases such as the CRISPR-Cas9 system. What was practically inconceivable – modifying just one detail in the whole DNA sequence of an organism in a near perfect way, and without causing serious side effects (off-target mutations and other unwanted effects) – has now come within reach. The obvious lack of safety at the present time is no longer a convincing ethical argument for rejecting human germline gene editing (hGGE) in principle. It is only an argument for the present time. This has been recognized by highly ranked regulatory advisory boards (National Academies 2017). The question needs to be clarified: Once it is safe enough, why should it not be done? Safety is, however, an issue at the present time; I will say a couple of things about this in Section 4.