The Cell Cycle & Mitosis

Where it all began……. You started off as a cell smaller than the period at the end of a sentence………

And now look at you! How do you get from being smaller than a “period” to a growing human being?

Getting from here to there Going from egg to baby…. the original fertilized egg has to divide… and divide…

Why do cells divide? Growth Repair Reproduction From fertilized egg to multicellular organism Repair Replace cells from normal wear and tear and injury Reproduction Asexual Reproduction (1 celled organisms) All of this happens through a Process called The Cell Cycle

The Cell Cycle The cell cycle is the process by which the cell grows and divides to make copies of itself. The life of a cell is divided into three stages: Interphase – The cell grows, DNA replicates, and the cell does the functions it is meant to do – i.e. create enzymes and proteins. Mitosis – The process the cell goes through to divide. Cytokinesis – The division of cytoplasm and organelles to create two separate cells. This is also the beginning of the interphase.

The Cell Cycle 1) Interphase has three parts - G1 Phase – Cells increase in size, growth of all parts of the cell continues, and cell actively does all the functions of a normal cell (creating proteins, enzymes and etc…). S Phase - The DNA is replicated G2 Phase – The cell continues to grow and prepares itself to enter the mitosis phase.

The Cell Cycle 2) Mitosis has four phases Prophase Metaphase Anaphase Telophase 3) Cytokinesis The cell fully divides into a sister cell.

The Cell Cycle 2 hours Cytokinesis Phase

Mitosis Interphase Prophase Metaphase 4. Anaphase 5. Telophase 6. Cytokinesis Nucleus Cytokinesis starts Chromosome Spindle Fibre 1 2 3 4 5 6

Interphase Cells are in Interphase for about 90% of their life Your cell muscles are constantly breaking apart and being replaced, the cells in your small intestine are constantly absorbing nutrients and cells are always dividing. A cell doing its “everyday job” as well by making proteins, enzymes, and etc… During interphase – DNA starts as chromatin (thread like appearance) During interphase DNA replication occurs

Interphase - DNA Replication We know that DNA can replicate by “unzipping” and then rejoining itself. Recall that the pairing of DNA has to stay constant, Adenine (A) - Thymine (T) and Guanine (G)- Cytosine (C).

Interphase - DNA Replication When DNA creates a copy of itself, the copy is called the Sister Chromatids. In the middle of the Sister Chromatids is the centromere. The Centromere - stays in the middle of the sister chromatids and holds the sister chromatids together.

Prophase – Part 1 of Mitosis Centrioles (or poles): Appear and begin to move to opposite sides of the cell. They produce spindle fibers, and help organize the spindle fibers during cell division Spindle Fibers : form and stretch across the centrioles at opposite ends of the cell

Prophase – Part 1 of Mitosis Chromosomes coil up into an X-Shaped chromosome. Chromosomes attach to spindle fiber at their centromeres. The nucleolus disappears and the nuclear membrane breaks down.

Spindle fibers Plasma Membrane Centrioles Centromere Nuclear membrane Sister Chromatids

Metaphase – Part 2 of Mitosis Spindle fibers, now fully attached to the centromere, pull the chromosomes towards the middle of the cell. The Chromosomes line up across the middle of the cell (the equator) and prepare to split apart.

Anaphase - Part 3 of Mitosis Sister Chromosomes separate at the centromeres. Spindle fibers pull the sister chromatids to the opposite side of the cell. 1 chromosome 2 sister chromatids Double Stranded 2 chromosomes Single Stranded

Telophase – Part 4 of Mitosis Spindle fibers disappear. Nuclear Membrane forms around each set of chromosomes. Chromosomes appear as chromatin (threads rather than rods). Note there are two nuclei in one (1) cell. Mitosis ends here.

Cytokinesis The Cytokinesis process is what starts the Mitosis phase. The cell membrane pinches together to divide the cells cytoplasm and organelles into two cells. The two nuclei are separated and two new daughter cells are formed. The new daughter cells are identical to the parent cell.

Chromosomes line up at the Equator Mitosis Chromosomes line up at the Equator Sister Chromosomes separate and are pulled to the opposite sides of the cell Cytoplasm divides and two new daughter cells are formed that are genetically identical to the parent cell

Video of The Cell Cycle https://www.youtube.com/watch?v=g7iAVCLZWuM