the cell cycle the cell cycle is the sequence of events that occur in a eukaryotic cell leading up...

The Cell CycleThe cell cycle is the

sequence of events that occur in a eukaryotic cell leading up to and including cell division.

The two major “parts” of the cell cycle are:InterphaseMitosis/Cytokinesis

InterphaseBefore a cell can

divide, it needs to acquire the necessary nutrients needed to divide as well as make other preparations.

All these things are done during a period of the cell cycle called Interphase.

InterphaseInterphase makes up

the majority of the cell cycle as the cell is usually spending most of its time growing and preparing to divide rather than dividing itself.

That is why Interphase is further subdivided into three stages.

Gap 1 (G1) PhaseThis first stage of

Interphase is where the cell grows and obtains nutrients needed for the creation of enzymes needed in future stages.

Synthesis (S) phaseThis part of

Interphase is where the cell’s DNA is copied, so that there are now two copies of each chromosome.

Gap 2 (G2) PhaseIn this final stage of

Interphase, the cell is preparing to divide.

It creates lots of microtubules, a special part of the cell’s cytoskeleton, which allows the cell to easily move contents around inside its cytoplasm.

MitosisOnce Interphase is

complete, the cell is ready to divide.

That division consists of two linked, but independent events known as mitosis and cytokinesis.

Mitosis is the division of the nucleus into two equal parts whereas cytokinesis is the separation of the cell’s organelles into the formation of two new cells.

MitosisMitosis deals solely

with the contents of the nucleus.

It consists of four “phases” which separate the chromosomes equally, creating two, genetically identical, daughter nuclei.

ProphaseThe first phase of mitosis.The nuclear membrane

dissolves.The chromosomes

become more visible and are attached to their copy by a special protein known as a centromere.

Special organelles known as centrioles move towards the “poles” of the cell.

MetaphaseChromosome pairs,

known as sister chromatids, line up at the “equator” of the cell.

Spindle fibres emerge from the centrioles and attach to the centromere of each chromosome pair.

AnaphaseThe spindle fibres

contract, breaking the centromere, and pull apart the sister chromatids.

One copy of the chromosome pair goes to one pole, while the other copy goes to the other pole.

TelophaseThe last stage of

mitosis, where the nuclear membrane starts to reform around the chromosomes that have been pulled to each pole and two new nuclei have formed.

The cell membrane starts to pinch inward at the equator signaling the end of mitosis and the beginning of cytokinesis.

CytokinesisCytokinesis means

“movement of cytoplasm”.

Once the cell has two new nuclei formed, it starts moving organelles to each pole and the cell membrane that has pinched inward at the middle will finally split the cell into two new, identical daughter cells.

Resting (G0) PhaseAfter

mitosis/cytokinesis, the cell goes through a brief resting stage before starting Interphase once again.

The length of the resting stage differs depending on the cell type.

ApoptosisOccasionally an error

may occur during Interphase or Mitosis which renders the cell useless.

These cells usually go through apoptosis, or programmed cell death (PCD) in which the cell is surrounded and destroyed before it can cause damage to surrounding cells.

CancerUnfortunately,

sometimes there are problems with the cell cycle itself causing cells to divide more rapidly than they are supposed to, which is called cancer.

CancerThe rapidly dividing cells

create a mass called a tumor.

Tumors can be benign or malignant.

The difference is that malignant tumors can invade adjacent tissues and use the circulatory or lymphatic systems to travel to and create cancer in other places in the body.

Benign tumors do neither of these and only produce a localized swelling or lump.

CancerScientists are

currently researching how cancer cells are created in the body in the hopes of shutting down this process and thus preventing many of the cancers present today.