Tutor profile: Ryan M.

Why is it more energetically favorable for water and oil to not mix?

By remaining separate, the water molecules are able to form hydrogen bonds with one another. If oil was mixed with water, fewer hydrogen bonds could be made between water molecules, which is not as stable energetically.

In regards to the CRISPR gene editing tool, why is the PAM sequence necessary?

The PAM sequence is adjacent to the guide RNA sequence in the target DNA. The PAM is necessary for Cas9 to cut the target DNA. Importantly, the PAM is not stored in the bacterial genome along with the guide RNA sequence. This means Cas9 will not cut the bacterial DNA where the guide RNA sequence is stored.

What is one reason why the cellular process of apoptosis is critical for an organism's survival?

In a case where DNA has not been faithfully copied, mutations can arise leading to unregulated growth of a cell. If allowed to continue growing unchecked, cancer can result. Luckily for us, apoptosis is one way to eliminate these erroneous cells before they multiply excessively.