1. 1.6 Cell Division/Mitosis

2. Question? Why would a cell want or need to divide?
Growth/development of tissues/organs
Repair of damaged tissue/organ
Reproduction of cells/organisms

3. Cell Cycle
The cell’s life cycle (usually just called the cell cycle) consists of two main parts:
Interphase – active period in the life of a cell when many metabolic reactions occur, including
protein synthesis
DNA replication
an increase in the number of mitochondria and/or chloroplasts
Mitosis – cell divides

5. Cell Cycle Interphase can be divided into three phases:
G1 – cell grows and metabolizes
S – DNA is replicated
G2 – cell prepares for division

6. Mitosis Mitosis can be divided into four stages: Prophase Metaphase
Anaphase
Telophase

8. Mitosis Prophase Nuclear envelope disappears
With the aid of special proteins called histones, DNA supercoils into distinct chromosomes that are visible under the microscope
Each pair of identical segments of DNA, called sister chromatids, bind together at the centromere to form one chromosome

10. Prophase Centrioles moved to opposite ends of the cell
Long, tubular proteins called “spindle fibers” grow from the centrioles and attach to the centromeres of the chromosomes

11. Metaphase
Spindle fibers pull chromosomes to the equator (center line) of the cell

12. Anaphase Spindle fibers shorten
Sister chromatids are pulled apart and are now called chromosomes
Chromosomes are pulled to opposite ends of the cell

13. Telophase Reverse of prophase: Spindle fibers dissapear
DNA uncoils and becomes chromatin
Nuclear envelope reforms

14. Cytokinesis Splitting of the cytoplasm
Occurs when microtubule proteins pinch inward at the equator (cleavage furrow)
Results in two separate but identical cells

15. Plant Cell Division
In plants a cell plate forms instead of a cleavage furrow

17. Overview Mitosis produces two genetically identical nuclei
During the S phase of interphase DNA is replicated to produce two identical copies
During prophase the identical copies of each chromosome (homologous chromsomes) bind together
Homologous chromosomes are pulled apart during anaphase and become part of two separate nuclei during telophase

18. Mitosis serves many purposes:
Tissue/organ growth
Embryonic devleopment, when the zygote divides to produce many smaller cells
Tissue damage and repair
Asexual reproduction (unicellular organisms)

19. Control of this process
Cyclins
Series of proteins that control cells during cell cycle.

20. Not always controlled Mutagens –
Physical or chemical agent that changes the DNA in an organism.
This increases the frequency of mutations in that organism above the natural background level.
Often these mutagens can cause cancer/tumors

22. Oncogenes
Sometimes the gene controlling cell division (called an oncogene) will become mutated
The result is that cell division continues repeatedly
This is how tumors are formed
Tumors can form in any tissue of the body
Stomach Tumor

23. Metastasis Greek for “Next Placement”
Cells that are going through uncontrolled proliferation can sometimes slough off of a tumor and spread through the body to another area that previously was unaffected.
These cells will continue their rapid mitotic division and cause the disease to spread.

24. Tumors
Tumors are a mass of cells that are going through mitosis uncontrollably due to a mutation in the DNA
Two major types:
Malignant: “Badly Born” can spread to invade other cells throughout the body.
Benign: lacks the ability to invade neighboring cells