Cell Division Ch 10 Sections 10-2 & 10-3

10-2 Cell Division In Eukaryotes (Cells with a nucleus) cellular division occurs in 2 stages: 1. Mitosis= 1 st stage where the cell’s nuclues divides 2. Cytokinesis= 2 nd stage where the cytoplasm divides

Chromosomes Chromosomes: Found in eukaryotic cells Pass genetic information from one generation to the next Made up of DNA The cells of every organism have a specific # of chromosomes EX: Fruit flies= 8 chromosomes, Humans= 46 chromosomes, carrot cells= 18 chromosomes Each chromosome is composed of two chromatids

Chromatids Chromatids: 2 identical strands that make up 1 chromosome During cell division, sister chromatids separate from each other One chromatid then goes to each of the 2 new cells

The Cell Cycle The Cell cycle= A series of events that cells go through as the grow and divide Cells grow Prepare for division Divide to form 2 daughter cells Each daughter cell then begins the cycle again

Events of the Cell Cycle Events of the cell cycle can be divided into two major stages: 1. Interphase= Can be quite long. Divided into 3 parts G1= Cells grow and increase their size S= Chromosomes replicate, DNA is synthesized G2= Produces organelles required for cell division 2. Cell Division= AKA Mitosis Takes place quickly

Mitosis Mitosis= Process of cellular division. Divided into 4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Prophase Prophase= 1 st and longest phase of mitosis (50- 60%) of total time required to complete mitosis Chromosomes become visible Centrioles (2 tiny structures located in the cytoplasm) separate and take opposite sides of nucleus Condensed chromosomes attach to the spindle Chromosomes coil more tightly Nuclear envelope breaks down & nucleolus disappears

Metaphase Metaphase= 2 nd phase of mitosis. Lasts only a few minutes Chromosomes line up in center of the cell Microtubules connect centromere of each chromosome to the 2 poles of the spindle

Anaphase Anaphase= 3 rd phase of mitosis Sister chromatids split & separate becoming individual chromosomes Chromosomes move into two groups near poles of the spindle Anaphase ends when chromosomes stop moving

Telophase Telophase= 4 th and final phase of mitosis Chromosomes begin to disappear into tangle of dense material Nuclear envelope reforms around each cluster of chromosomes Spindles break apart Nucleolus becomes visible in each daughter nucleus Mitosis is complete ** CELL DIVISION HOWEVER IS NOT COMPLETE**

Cytokinesis Cytokinesis= Division of the cytoplasm itself and is the final phase of cellular division Usually occurs during the same time as telophase In animal cells= cytoplasm is drawn inward and pinched into two equal parts In plant cells= Cell plate forms causing a cell wall to form between the 2 divided nuclei

10-3 Regulating the Cell Cycle Controls on Cell Division: Cell growth can be turned on and off depending on the situation EX: if cells growing on a Petri dish are removed, the cells surrounding that now empty space will start dividing, filling in the area where the cells were removed

Cell Cycle Regulators Cell Cycle Regulators= Help maintain homeostasis (relatively stable environment) in the body. Cyclins= A family of closely related proteins that regulate the timing of the cell cycle in eukaryotic cells Internal Regulators= Proteins that respond to events inside cell Allow the cell cycle to proceed only when certain processes have happened inside the cell. EX: Several proteins make sure cell doesn’t start mitosis until all chromosomes have been replicated.

Cell Cycle Regulators Con’t… External Regulators= Proteins that respond to events outside the cell. Direct cells to speed up or slow down the cell cycle. EX: Growth regulators are important during embryonic development & wound healing EX: molecules on neighboring cells can cause cell cycles to speed up or slow down keeping tissues of the body from disrupting each other.

Uncontrolled Cell Growth The consequences of uncontrolled cell growth in multicellular organisms can be very severe. Cancer cells DO NOT respond to the signals that regulate the growth of most cells They divide uncontrollably forming tumors Some fail to respond to internal regulator proteins Some fail to respond to external regulator proteins Causes of cancer can be: smoking, radiation exposure, and even some viral infections