Cell Cycle: Mitosis Cell Growth and Division

Mitosis In asexual reproduction, one parent produces genetically identical offspring by mitosis. A life cycle is the generation-to- generation sequence of stages in the reproductive history of an organism

Cellular Division Multicellular organisms depend on cell division for: – Development from a fertilized cell – Growth – Repair

1. Why do cells divide?  If the cell is too big: Too much demand is placed on DNA Too much demand is placed on DNA Harder to move enough nutrients and wastes across the cell membrane Harder to move enough nutrients and wastes across the cell membrane DNA: DNA molecules in a cell are packaged into Chromosomes. DNA (its genetic information) is called its genome

2. Surface area vs. volume

2. Surface Area vs. Volume  As a cell increases in size, volume increases faster than surface area  This causes the ratio of surface area to volume to decrease.  This is a serious problem for the cell and is why the cell cannot grow any larger than it does.

3. Cell division solves those problems  Before a cell becomes too large, a growing cell replicates its DNA and then divides into two new “daughter” cells. This process is called mitosis.

Main Events of a Cell Cycle  Interphase G1, G1, S G2 G2  M Phase Prophase Prophase Metaphase Metaphase Anaphase Anaphase Telophase Telophase 

Interphase  Chromosomes are copied (# doubles)  Chromosomes appear as threadlike coils (chromatin) at the start, but each chromosome and its copy (sister chromosome) change to sister chromatids at end of this phase

Prophase  Mitosis begins (cell begins to divide)  Centrioles (or poles) appear and begin to move to opposite ends of cell  Spindle fibers form between the poles

Metaphase  Chromatids (or pairs of chromosomes) attach to the spindle fibers

Anaphase  Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell

Telophase  Two new nuclei form  Chromosomes appear as chromatin (threads rather than rods)  Mitosis ends

Cytokinesis  Cell membrane moves inward to create two daughter cells - each with its own nucleus with identical chromosomes

Label the stages

What stops cell from growing?  Proximity to neighbor cells. Cells in a petri dish will continue to grow until they come into contact with other cells. Cells in a petri dish will continue to grow until they come into contact with other cells. Similarly, skin around a wound will continue to grow until they come into contact with other cells. Similarly, skin around a wound will continue to grow until they come into contact with other cells.

Which chemicals regulate the cell cycle?   The chemicals that regulate the cell cycle are cyclins.   There are about a dozen of proteins which help regulate the cell cycle. They work by regulating the timing of the cell cycle in eukaryotic cells.

How do cells respond to contact with other cells?   Chromosome damage builds up when cells respond to contact with other cells. Damage incurred to its DNA, can enter one of three possible states: 1. An irreversible state of dormancy, known as senescence senescence 2. Cell suicide, also known as apoptosis or programmed cell deathapoptosisprogrammed cell death 3. Unregulated cell division, which can lead to the formation of a tumor that is canceroustumorcancerous

How are cancer cells different from other cells?   Cancer can be considered a disease of the cell cycle because it breaks down the cell cycle and some cancer cells don't respond to the external growth regulators, while some fail to produce the internal regulators that ensure orderly growth.   Uncontrolled cell division