Cell Cycle

The cell cycle is the life cycle of a cell from the moment it becomes a new cell to when it splits.

The first half of its life is called G1. It is normal cell function and growth. The cell is doing its job. The job depends on what it’s for. This is the only part, it’s good at its job. If a cell skips G1, then it turns into cancer because it can’t do its job and keeps dividing.

At the half point, a signal is sent when the ratio of circumference:area is 1:13. It gets too large for things to happen correctly. The message is sent to the fat to tell the cell to divide because it’s too big!

The following section is the S phase. This is when the DNA duplicates. This is so that both cells will have the DNA. This is the phase that goes before mitosis. This is when the DNA starts to suck. S= DNA duplication.

The next phase is called G2 and is the part that prepares for division. This is the second-largest part. G2= cell prepares to divide.

The next phase is the shortest and is called the M phase. M is when the cell divides. If it is Eukaryotic, then it goes through mitosis (nucleus dividing). Cytokinesis then happens (cell dividing) (not necessarily in that order). In prokaryotic cells they don’t do that, so they do binary fission.

Eukaryotes have a nucleus and prokaryotes don’t. We are eukaryotes and bacteria are prokaryotes. Eukaryotes are made of cell membranes.

Mitosis and Cytokinesis

Chromatin- a relaxed form of DNA, enzymes can get through and genes can be expressed. It is very easily broken.

Chromatid- The copy and the original of the DNA together during the S phase, often called sister chromatids.

Chromosome- the DNA that is wrapped over itself and is ready to travel for mitosis. It is packaged safely, but can’t do what it’s supposed to do.

Mitosis is the nucleus replicating. Mitosis needs to happen before cell division because without it one cell would have no nucleus and it wouldnt have any DNA to make proteins. Each new cell will need its own nucleus. Interphase is the largest part of the cell cycle. Interphase is G1, S, and G2 phases of the cell cycle, but it is NOOOOOT part of mitosis.

Centriole is a large part in mitosis and is a minute tube-shaped organelle.

There are four phases of Mitosis(in order) is prophase, metaphase, anaphase, and telophase.

Prophase

is the first phase and the first thing that happens is the chromatin condenses into a chromosome. At this point, if you were looking at a human skin cell you would be looking at 92 chomosomes. The next step is the nucular membrane (also called envelope) disolves. If the membrane didnt dissolve then the chromosomes couldnt seperate out because the membrane is holding it together. The third part is that the centriols goes to the opposite side of the cell. The last thing that happens is the spindle fibers form. Spindle fibers come out of the centrioles and towards eachother. They are proteins.

Metaphase

is the second phase. There is a metaphase plate which is just as symbolic as the equater, which we can measure but its not tangible. Its at the middle of the cell. The chromosomes line up on the metaphase plate with sister chromatids across from eachother. The choromosomes attach to the spindle fibers.

Anaphase

Anaphase is the third and it is EASY. All that happens in anaphase is where the spindle fibers pull the dna closer to the centrioles.

Telophase

Telophase is the last phase. The first thing to happen is the nuclear membrane reforming around both cells so it has two nuclei. Then the chromosomes relax into chromatin and the spindle fibers dissolve. What happens next depends on what type of cell it is.

Cytokinesis

If it is a plant cell then it has a cell wall. In this case,

1. a cell plate forms in the middle- dividing the cell.

2. the cell wall breaks and the membrane goes with it.

If it is an animal cell then it doesnt have a cell wall. The cleavage furrow (lol) forms and the cell wall just pinches in half.