`THE LIFE OF A CELLLearning Objectives:1. List the stages of the cycle and the events that occur in each stage.2. Provide examples of cells that cannot divide, those that divide when stimulated byspecific conditions and cells which continuously divide.3. Define the terms related to important structures involved in mitosis.4. List the phases of mitosis and the major events that occur in each phase.5. Discuss the difference between mitosis and meiosis.6. Define the terms used to describe cellular adaptations.In humans, approximately 100 BILLION cells die every 24 hours. Replacement of the cellsis ongoing. How is it accomplished?THE CELL CYCLESTAGES OF THE CELL CYCLE PRINCIPLE EVENTSI. INTERPHASEA. G1 phase – Normal cellular activities. Cell growth and duplication of organelles. B. S phase – DNA replication (most vulnerable phase)C. G2 phase – Synthesis of protein, microtubulesII. MITOTIC PHASE(See later section for Stages)Cell II - Page 1 of 5General InformationA. Possible fates of mitotic products (daughter cells)1. differentiate (specialize)  age  die2. rest as an “uncommitted” cell3. enter a new cell cycle immediatelyB. The capacity to grow and divide varies with the cell type. The rate at which these processes occur also varies. There are three major categories:1. Cells which are extremely specialized and have lost their ability to divide.a. RBCs (mature)b. Neurons (nerve cells)c. muscle celss (may increase in size, not in number)2. Cells that normally do not divide, but can be induced to do so by a stimulus.a.liver cellsb. lymphocytes (WBCs) 3. Cells which continuously undergo cell division. (cells subject to destruction, friction.)a. Skin (constantly replaced)b. Cells of intestinal lining c. Bone marrow cellsTerminology Related to Cell Division: Chromosome- Dark staining, threadlike body in the nucleus composed of DNA and protein - Contains genetic infoChromatid- Gene - Unit of dna that provides instruction for the produ8ction of a specific protein, centriole Gene- Unit of dna that provides instruction for the produ8ction of a specific protein, centriole Cell II - Page 2 of 5Centriole- composed of microtubules- 2 cylindrical structure - serves as organizing center for the mitotic spindle Mitotic SpindleKaryotype- a number and type of chromosomes an individual has - a normal karyotype has 23 paris of chromosomes= 46 - 22 pairs autosomes and one sex chromosomes CELL CYCLE1. INTERPHASE – Recall that: period of cell growth and dna replication- This is the non-dividing stage of the cell cycle during which the cell is involved in DNA replication and growth- During the S phase the cell is very vulnerable to events which can cause DNA damage since replication of DNA occurs during this stage- Rapidly dividing cells, such as those of the skin, digestive (GI) tract and bonemarrow are especially vulnerable.2. MITOSIS Mitotic Stage Distinguishing Features/Events PROPHASENuclear membrane disappearsChromosmes become condensed Centrioles migrate to opposite sides of poles in cell METAPHASEPaired chromosomes line up along the equator of cell ANAPHASEChromosomes separate and migrate to opposite sides ofcellCell II - Page 3 of 5TELOPHASENucleus divides into 2 identical cells that have the same compositon of dnaCytokinesis occurs Result of Mitosis: Ultimately, two identical daughter cells are produced. These cells will then enter the phases of the cell cycle and may immediately divide again, “rest” or remain permanently in interphase. MITOSIS Vs MEIOSISKEY FEATURES of MITOSIS1. occurs in most cells of body2. results in 2 daughter cells3. daughter cells contain dna identical to parent cell4. each ahs 23 pairs of chromosomes= 46 total KEY FEATURES OF MEIOSIS1. occurs in sex cells (ova and sperm) located in gonads (ovary and testes)2. results in 4 daughter cells3. daughter cell contains ½ of dna CELLULAR ADAPTATIONSCell II - Page 4 of 5Many cells have the ability to undergo changes in response to stimuli (e.g. hormones)or injury (e.g. mechanical friction) in an attempt to adapt to altered or unfavorableconditions.Examples:1. Hypertrophy- increase in cell size2. Atrophy- means not or none. Decrease in cell size3. Hyperplasia- increase in mitotic activity and number of cells 4. Metaplasia- changes in cell in response to disease or chronic irritation which results in the transformation of the cell into a different cell type 5. Neoplasm- new cell mass. Rapid multiplication- Benign- MalignantCell II - Page 5 of