To maintain healthy life the information stored in genes must be protected. However, DNA can be damaged by various factors, most notably exposure to the sun. DNA damage often takes the form of physical breaks in the DNA sequence, turning a long string of nucleotides into two shorter strings.
In order to survive it is essential that DNA damage is repaired. Small changes in the DNA sequence are referred to as mutations. Some mutations have little or no effect on the information stored in DNA, but others can cause a gene to be corrupted. At worst, the gene can be entirely inactivated and its information lost. The functional loss of a gene i. The individual genome editing techniques have their own details, but their concepts are similar. Scientists design the endonucleases to only cut the DNA at a location they have chosen, usually an important part of a gene of interest.
If the endonuclease has been designed correctly, DNA will be cut but poorly repaired, with some nucleotides lost or gained. The result is the corruption of that gene. But genome editing can do more than just knockout a gene. Scientists have learned how to change the information stored in DNA in more sophisticated ways.
For example, tiny changes in the DNA sequence that might cause a disease can be made. Similarly to gene knockout, this more complicated genome editing also begins with the targeted cutting of DNA within a chosen gene, but the process of DNA repair is different. Scientists have learned how to activate an alternative DNA repair mechanism and trick it into making pre-planned mistakes.
To do this, at the same time the endonuclease is added to the cells, a small piece of specially made DNA is also introduced. This DNA molecule has almost the same sequence as the gene that is being cut, but contains some minor differences that correspond to the mutation the scientist wants to make.
If everything goes to plan, the cell will repair its damaged DNA, but will incorporate the desired mutation into the gene. Genome editing is thus based on the use of engineered molecules that target and cut a specific site in a gene.
The applications are various, from understanding the function of a gene by generating genetically modified animals or cells, to gene therapy, drug research, and even agriculture.
More importantly yet, the use of genome editing continues to grow and it is likely that these technologies will accelerate research, leading to important scientific breakthroughs in years to come.
In November , a team of scientists in China led by Dr. Two of the embryos were successfully implanted in a surrogate, resulting in twin girls. Now known only as Nana and Lulu — their identities protected in scientific version of the witness protection program — Dr.
He and his collaborators were recently sentenced by a court in Shenzhen to three years in prison for conducting "illegal medical practices. The technology has a massive range of applications, and those applications carry different degrees of risk, depending on the kinds of cells edited.
Maybe you remember the distinction of somatic versus non-somatic cells from biology? Most of your cells are somatic: your eyes, your lungs, your heart. For non-somatic, think sperm, eggs, embryos, stem cells: the cells directly used to create offspring. The difference is relevant because genetic modifications to reproductive non-somatic cells get passed on to the descendants of those organisms.
Companies working on next-generation antibiotics have developed otherwise harmless viruses that find and attack specific strains of bacteria that cause dangerous infections. Meanwhile, researchers are using gene editing to make pig organs safe to transplant into humans. Gene editing has transformed fundamental research too, allowing scientists to understand precisely how specific genes operate.
So how does it work? There are many ways to edit genes, but the breakthrough behind the greatest achievements in recent years is a molecular tool called Crispr-Cas9. When the cell tries to fix the damage, it often makes a hash of it, and effectively disables the gene. This in itself is useful for turning off harmful genes.
But other kinds of repairs are possible. For example, to mend a faulty gene, scientists can cut the mutated DNA and replace it with a healthy strand that is injected alongside the Crispr-Cas9 molecules. Different enzymes can be used instead of Cas9, such as Cpf1, which may help edit DNA more effectively.
Remind me what genes are again? Genes are the biological templates the body uses to make the structural proteins and enzymes needed to build and maintain tissues and organs. They are made up of strands of genetic code, denoted by the letters G, C, T and A. Humans have about 20, genes bundled into 23 pairs of chromosomes all coiled up in the nucleus of nearly every cell in the body.
Only about 1. The rest of our DNA is apparently useless. What are all those Gs, Cs, Ts and As? The letters of the genetic code refer to the molecules guanine G , cytosine C , thymine T and adenine A. It takes a lot of them to make a gene. The gene damaged in cystic fibrosis contains about , base pairs, while the one that is mutated in muscular dystrophy has about 2.
Each of us inherits about 60 new mutations from our parents, the majority coming from our father. But how do you get to the right cells? This is the big challenge. Most drugs are small molecules that can be ferried around the body in the bloodstream and delivered to organs and tissues on the way.
The gene editing molecules are huge by comparison and have trouble getting into cells. But it can be done. One way is to pack the gene editing molecules into harmless viruses that infect particular types of cell.
Millions of these are then injected into the bloodstream or directly into affected tissues.
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