Why is cell division necessary? (Zygote or fertilized egg) The actual process of cell division constitutes a short period in what is called

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1 Mitotic Cell Division When a cell undergoes reproduction, or cell division, two daughter cells are produced that are genetically identical to each other and to the parent cell. 1) Growth Increase in size of the organism Egg Spermatozoid fertilization Why is cell division necessary? (Zygote or fertilized egg) 2) Maintain the body Continuing replacement of aging or lost cells About 50 millions of cells die per second: red blood cells, cells of the gut, skin 3) Repair Damaged tissues: broken bone, skin cells destroyed by abrasion The actual process of cell division constitutes a short period in what is called The cell cycle Basic life cycle of all cells, two things happen Cells conduct metabolic activities and divide The amount of time cells spend in each stage depends on the type of cell Mitosis + Cytokinesis (Reproductive phase) G2 Interphase (Metabolic phase) During interphase G2, a cell: Doubles everything in its cytoplasm Grows in size Cell division (10%) Metabolic Activities (90%) S: DNA synthesis (replication) G1 During interphase G1, a cell: Performs its normal functions 1

2 Mitosis and Cytokinesis 2 main processes in cell division: Mitosis The nucleus and its contents divide evenly into two daughter nuclei, the genetic information (DNA) is equally distributed to the two daughter cells Cytokinesis Cell splitting, the cytoplasm is divided in two 2 daughter cells INTERPHASE: Before a parent cell splits into two, it duplicates its DNA, called chromatin during this stage. MITOSIS Nuclear division CYTOKINESIS Cell splitting Eukaryotic DNA In a eukaryotic cell: Most genes are located on long strands of DNA in the cell nucleus, called chromosomes each chromosomes typically bears thousands of genes Units of genetic information The number of chromosomes in a eukaryotic cell depends on the species. Human karyotype 2

3 Eukaryotic DNA Is organized in bundles called chromosomes: Are made of chromatin, a combination of DNA and protein molecules Are not visible until cell division occurs 1) DNA (chromosomes) duplication 2) Chromosomes packing for cell division (non duplicated DNA) Most of the DNA is duplicated during S part of Interphase. The only part not duplicated is the centromere that connects both sister chromatids Interphase Right before cell division, the cell: Duplicates its DNA (S part) and doubles everything in its cytoplasm (G2) in preparation for cell division DNA appears all homogeneous inside the nucleus (uncoiled) 3

4 Mitosis: Prophase Chromatin in the nucleus condenses and becomes visible in the light microscope as chromosomes. Nucleolus disappears. Centrioles (only present in animal cells) begin moving to opposite ends of the cell Nuclear membrane disappears Spindle fibers extend from centriole to centriole (pole to pole) Mitosis: Metaphase Centrioles are at the poles of the cell and spindle fibers extend from pole to pole Chromosomes align at the equatorial plane. Chromosomes still consist of two chromatids attached to the spindle 4

5 Mitosis: Anaphase Centromeres replicate Chromatids separate and migrate to opposite poles by a motor protein (kinetochore), with the aid of ATP Each chromatid moving to the opposite pole is the exact copy of the other Mitosis: Telophase Everything inside the cell goes back to interphase! 2 new nuclear membranes are reformed. 2 Nucleolus reappears Chromosomes disperse and are no longer visible under the light microscope (the DNA uncoils) The spindle fibers are no longer needed, so they break down Important! Centrioles are NOT present in plant cells, but cell division happens in the same way 5

6 Cytokinesis Overlaps with telophase Divides the cytoplasm in two new cells Is different in plant and animal cells as a result of the cell wall present in plants Animal cells A fiber ring around the center of the cell, composed of a protein called actin contracts pinching the cell into two daughter cells, each with one nucleus. Plant cells In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells Cancer: Abnormal Cell Division Cells go through uncontrolled cell division becoming cancerous cells or tumors a cancer is mass of undifferentiated cells not normally present in the body. Uncontrolled cell division in white blood cells causes leukemia Benign tumor Cell mass does not fragment and spread beyond its original area of growth Malignant tumor Cell mass spread and invade other parts of the body (metastasize) Chemotherapy (destroy mitotically dividing cancer cells) and radiation (induces apoptosis: programmed cell death). 6

7 Other Cancer treatments Differentiation: process of forming specialized cells within a multicellular organism. Some cells retain the ability to divide and specialize into diverse types of cells GERSON THERAPY Documentary:The Beautiful Truth (2008, Steve Kroschel) The Gerson Therapy is a natural treatment that activates the body s extraordinary ability to heal itself through an organic, vegetarian diet, raw juices, coffee enemas and natural supplements BURZYNSKI THERAPY Documentary:Burzynski, Cancer is a serious business (2010, Eric Merola) The approach to treatments is based on the natural biochemical defense system of our body, capable of combating cancer with minimal impact on healthy cells. Cells Differentiation: Stem Cells Differentiation: process of forming specialized cells within a multicellular organism. Some cells retain the ability to divide and specialize into diverse types of cells Ovum (egg) Spermatozoid fertilization (Zygote or fertilized egg) Mitosis Blastocyst (embryo) Adult Stem cells Circulating blood Red bone marrow Skin Limited ability to differentiate into other type of cells Embryonic Stem cells Capacity to differentiate into any type of cell (tissue) Mitosis 7