Cutting with Precision: Cas9 Protein Function

If an enzyme is designed to break the phosphodiester bonds of a nucleic acid, then it is a nuclease. Since Cas9 physically cuts DNA, then it is classified as a nuclease.

If a tool is capable of slicing through a double-stranded molecule to stop a process or change a code, then the "scissors" analogy is accurate. If Cas9 performs this cut, then the statement is true.

If bacteria need to defend themselves against viruses, then they use specialized proteins to destroy viral DNA. If Cas9 is that defense protein, then it is part of the bacterial immune system.

If Cas9 is a programmable cutter, then it needs a "map" (gRNA) and a "target" (DNA). If it also needs a "safety check" to avoid cutting itself, then the PAM sequence is a requirement.

If Cas9 needs to distinguish between the cell's own DNA and an invader, then it looks for a specific code called a PAM. If the PAM is present next to the target, then Cas9 will bind and cut.

If the genetic code is universal, then a protein designed to cut DNA can work in any cell. If Cas9 is introduced into human or plant cells, then it can cut that DNA as well, making the statement false.

If Cas9 uses two different active sites to cut both sides of the DNA helix at once, then the result is a complete snap known as a double-strand break.

If a DNA molecule has two strands and Cas9 creates a clean break, then both strands must be cut. If HNH and RuvC are the active sites, then they are responsible for cutting the individual strands.

If a scientist only needs to change a short RNA sequence to target a new gene, then the system is highly flexible and efficient. If it hits the exact spot intended, then it is precise.

If Cas9 has no internal way to "read" DNA sequences, then it is "blind" on its own. If it hitches a ride on a gRNA that matches a gene, then it can find its destination.

If the guide RNA has a sequence like A-U-G and the DNA has T-A-C, then they will stick together. If they stick based on these chemical rules, then it is complementary base pairing.

If a cell detects a broken chromosome, then it must fix it to survive. If the repair is messy and adds or deletes bases, then the gene is "knocked out" or mutated.

If Cas9 is built from a chain of amino acids by a ribosome, then it is a protein. If it is a protein, then saying it is an RNA molecule is scientifically incorrect.

If the guide RNA provides the "address" for the cut, then the length and order of that address determine the accuracy. If the standard guide is 20 bases long, then that sequence dictates where Cas9 will land.

If certain genes are always found located next to the CRISPR DNA repeats, then they are logically linked to them. If they are linked, then they are "associated" with the CRISPR system.

If Cas9 can edit any gene, then it can fix mutations or improve plant survival. While it can alter biology, it cannot change the chemical properties of elements or grant human speech to animals.

If an enzyme acts as a catalyst, then it is not consumed in the reaction. If Cas9 remains functional after the cut, then it can float away and find another matching target to cut again.

If Cas9 is structurally designed to unzip and cut a double-helix of DNA, then it is a DNA-targeting enzyme. Other Cas proteins (like Cas13) target RNA, but Cas9 is for DNA.

If the bacterium saves a "spacer" in its own genome, then the matching part on the invading virus is the "proto" (original) version. This target is the protospacer.

If a natural bacterial defense can be reprogrammed to edit any living organism, then it is a massive breakthrough. If these two scientists were the first to prove this in 2012, then they earned the Nobel Prize.