2020 Nobel Prize in Chemistry
Reason for Award
for the development of a method for genome editing (CRISPR/Cas9 genetic scissors)
Laureates
France
United States of America
Explanation
Our bodies have a plan called DNA. Ms. Charpentier and Ms. Doudna discovered a pair of scissors that can cut and rewrite that plan. The scissors are called “CRISPR/Cas9.” Just like erasing a wrong word with an eraser and writing the correct one, scientists can fix mistakes in genes. This may help cure diseases or make stronger plants. In the future, the tool could become very important for helping people and animals.
Related Keywords
CRISPR
A set of repeated DNA sequences in bacteria and archaea that stores pieces of invading viral DNA as spacers. Upon reinfection, the stored information is transcribed into guide RNAs that recognize and direct cleavage of matching viral DNA. Thus CRISPR acts as a molecular memory of past infections, forming part of a prokaryotic adaptive immune system. Genome-editing technologies harness CRISPR’s intrinsic sequence-specific recognition capability.
Cas9
One of the CRISPR-associated proteins that cleaves double-stranded DNA at sequence-specific sites. Cas9 contains two nuclease domains—HNH and RuvC-like—that cut each DNA strand after the sgRNA-target duplex and PAM are bound. The 160 kDa Streptococcus pyogenes Cas9 (SpCas9) is the most widely used variant. Engineering has yielded nickase and catalytically dead forms that serve as platforms for extended functionalities.
guide RNA
A single-stranded RNA created by fusing crRNA and tracrRNA; its 20-nt spacer region dictates target specificity. The guide RNA forms a complex with Cas9, serving as a molecular antenna to locate complementary DNA sequences. Because changing only the spacer sequence retargets the system, sgRNA underpins CRISPR’s versatility. Chemical modifications and stabilizing motifs can improve intracellular stability and specificity.
genome editing
A collection of techniques that allow deliberate introduction of mutations, insertions, or deletions within a genome. Compared with older methods such as ZFNs and TALENs, CRISPR/Cas systems are easier to design and more efficient. Medical uses include treating genetic disorders, engineering cancer-fighting immune cells, and purging viral genomes. In agriculture, genome editing enhances yield, stress tolerance, and biofuel traits. International guidelines are required to address ethical and safety concerns.
DNA repair
When double-strand breaks occur, cells predominantly repair them via non-homologous end joining (NHEJ) or homology-directed repair (HDR). After CRISPR/Cas9 cleavage, NHEJ generates indels, whereas HDR enables precise edits guided by a donor template. Editing efficiency depends on the cell cycle stage and donor DNA format. Strategies such as Rad51 overexpression and chemical inhibitors have been developed to bias cells toward HDR. Repair pathway choice ultimately dictates the editing outcome.
gene therapy
A therapeutic approach that repairs, replaces, or inactivates disease-causing genes. CRISPR/Cas9 is in clinical trials for blood disorders such as β-thalassemia and sickle cell disease, where patients’ own hematopoietic stem cells are edited ex vivo and reinfused. In vivo delivery uses lipid nanoparticles or AAV vectors to target organs like the liver or eye. Long-term safety, immune responses, and off-target mutations remain critical evaluation points.
off-target effect
A phenomenon in which CRISPR/Cas9 erroneously cuts non-target sequences. Cas9 can tolerate several mismatches, causing unintended mutations. Genome-wide detection methods such as GUIDE-seq and CIRCLE-seq identify these sites. High-fidelity Cas9 variants and advanced guide-RNA design algorithms reduce off-target activity, but rigorous assessment is essential before clinical use.