Why Do Cells Need To Divide? It depends on the organism Unicellular organisms like bacteria (prokaryotes) divide to reproduce Multicellular organisms (most eukaryotes) use it to grow larger and repair damaged cells.
3 Types of Cell Division 1. Binary fission-cell division in prokaryotes 2. Cell Cycle (with Mitosis)-cell division in eukaryotes 3. Meiosis—cell division to form sex cells (egg and sperm)
Prokaryotes Divide by binary fission Circular DNA Results in two cells genetically the same What has to take place before the cells divide?
Eukaryotes The Cell Cycle – Growth – Repair or replacement of cells. Some cells die quickly and need to be replaced a lot (skin cells). Some cells never get replaced (nerve cells). Some organisms can regenerate whole body parts.
Each cell goes through a series of phases throughout its life. The cell cycle-all events between one cell division and the next **ONE REPLICATION & ONE DIVISION 2 basic steps: Interphase (G1, S, G2) and Mitosis (M) Result? 2 daughter cells genetically exact to the parent cell they came from.
First stage in Interphase G=gap Newly formed cell will go through intense growth. Takes in lots of food and energy. DNA at this point is unwound and called chromatin Interphase
Second stage in Interphase S=Synthesis phase. All DNA gets replicated during this phase cell has double the genetic material (92 chromosomes)
Third stage in Interphase G=gap Cell grows some more. Extra organelles are being made.
After Interphase (G1, S, and G2) M=Mitosis Mitosis = Nuclear division. MITOSIS IS THE DIVISION OF THE NUCLEUS DURING THE CELL CYCLE!!! There are four mitotic steps: – Prophase – Metaphase – Anaphase – Telophase.
Prophase Nuclear envelope will disappear. Spindle fiber forms.
Metaphase Chromosomes begin to line up at the equator of the cell. Spindle fibers attach to the center of each sister chromatid of the chromosome.
Anaphase Spindle fibers begin to pull apart sister chromatids. Each is now a chromosome Spindle breaks down after this.
Telophase Each side now has a full set of chromosomes. Nuclear envelope will reform.
Cytokinesis “Cytokinesis”—division of cytoplasm (cleaving the cell in half.) Animal cells form a “furrow.” Plant cells form a new cell wall. Formation of two, identical daughter cells with 46 chromosomes At first new cells are smaller than the originals.
REGULATION OF CELL CYCLE Cell division controlled by certain proteins called cyclins Cancer cells don’t respond to the cyclin signals--- uncontrolled growth (tumors) Benign tumors stay intact Malignant tumors spread throughout body (metastasize)