Okay, so let's take a look at DNA replication. A couple of reminders about DNA replication during the synthesis phase. It's when this happens and DNA replication involves DNA polymerase. So DNA polymerase, this is the enzyme that reads one strand of DNA and builds a complementary partner to it. So it carries out base pairing and catalyzes the reaction between adjacent nucleotides. One interesting note about DNA synthesis, so this is how our chromosomes get replicated. However, if you think about it, when polymerase makes it to the very end of the chromosome, what happens? There's actually going to be a little section right at the very end that doesn't quite get duplicated. And this brings us to a note about two amirs. Filamirs are the ends of chromosomes. And what happens during successive rounds of cell division is that our telomeres actually get shorter. So initially, like a brand new cell, initially it's going to have a chromosome that has nice long telomeres. The telomeres are repetitive at sections at the ends of the chromosomes. And each time the cell goes through cell division cycle, just a little bit at the end, sort of gets cut off. DNA polymerase just can't quite make it to the last few nucleotides. So each round of cell division, the telomeres get a little bit shorter and shorter. Eventually, this is going to start causing problems. And this is thought to be one of the things that contributes to aging. It's just the fact that our chromosomes get shorter with successive rounds of cell division. So eventually, this is going to start chopping off portions of important genes, right? So essentially, there's a limit to how many times cells can divide without experiencing some sort of damage. Damage telomeres tend to activate a number of different things, the gene P53, which then causes apoptosis or programmed cell death. However, we do have some special cells that are able to elongate their telomeres. So that's a very focused area of study right now when it comes to people who do research in aging, studying these cells that are able to elongate their telomeres. That's a really interesting thing. Turns out they have a special enzyme, it's called telomerease, and it can essentially come over and add new sections onto those shortening ends. So that's just in some special cells, like bone marrow, they can divide indefinitely. When we're talking about cells growing and dividing, when we talk about growth, there are really two different things we could be talking about, and this is just kind of a note, this will come up a couple of times throughout the semester. We could be talking about cells that grow and become larger. So each of the individual cells is getting larger in this schematic. That's one type of growth. That's called hypertrophy. This is what muscle cells can do. If you work out a lot, your muscles start to get bigger. That's hypertrophy. It's not that you're gaining more muscle cells. It's just the cells that you have are getting larger. The other type of growth is when the cells actually divide, and that's called hyperplasia. This is the one that involves mitosis. This is what we'd like to review right now in this chapter. It's just that process of cell division. So hyperplasia.