ANA 113 1stEdition Lecture 2 Outline of Current Lecture THE LIFE OF A CELLCurrent Lecture In humans, approximately 100 BILLION cells die every 24 hours. Replacement of the cell is ongoing.How is it accomplished?THE CELL CYCLE STAGES OF THE CELL CYCLE PRINCIPLE EVENTSI. INTERPHASE: consist of 3 phases- G1- S - G2 A. G1 phase:Normal cellular activities, cell growth & duplication of organelles. Protein synthesis.B. S phase:DNA replication. Chromosome duplication. Histones and centrioles replicate.C. G2 phase:Synthesis of protein, microtubules, etc.II. MITOTIC PHASE: - Nuclear division - Cytokinesis: cytoplasmic divisionGeneral Information: A. Possible fates of mitotic products (daughter cells)1. Enter a new cell cycle2. Rest as an “uncommitted” cell 3. Differentiate (specialize)  age  dieB. 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. Red blood cells (mature) no nucleusb. Neuron (nerve cell)c. Muscle cell (increase in size, not number)2. Cells that normally do not divide, but can be induced to do so by appropriate stimulus.a. Liver cellsb. Lymphocytes (white blood cells)Uncommitted3. Cells which continuously undergo cell division. (Includes cells subject to destruction, friction.)Differentiatea. Skin (constantly replaced) b. Cells of the intestinal lining c. Bone marrow cells.*Cell that divides rapidly is exposed frequently*Terminology Related to Cell Division:Chromosome: Dark staining thread-like body in the nucleus containing genetic information. Chromatin: DNA and proteinChromatid: Duplicated chromosomesGene: Gives hereditary unit or source of information for synthesis. Segment or portion of DNA on chromosome.Karyotype: The number and type of chromosomes an individual has- 23pairs.Centriole: Cylindrical structure composed of microtubules. Serves as organizing center for the mitotic spindle.Mitotic Spindle: (1) INTERPHASE – Recall that:-this is the non dividing stage of the cell cycle-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 the supplication of DNA occurs during this stage.-Rapidly dividing cells, such as those of the skin, GI tract, and bone marrow are especially vulnerable.(2) MITOSISMitotic Stage Distinguishing Features/EventsPROPHASE The nuclear membrane disappears and chromosomes become condensed. Compact. METAPHASE The paired chromosomes line upalong the equator of the cell.ANAPHASE The chromosomes separate and migrate to opposite sides (poles) of the cell.TELOPHASE The nucleus divides into two units which have the same composition ofDNA.Result of Mitosis- Ultimately two identical daughter cells are produced. These cells will then enter the phases of the cell and - May immediately divide again, “Rest” or remain permanently in Interphase.MITOSIS VS MEIOSISFEATURES OF MITOSIS1. Cell division2. Occurs in most cells of the body 3. Results in 2 daughter cells identical to parent cell.4. 23 pairs of 46 chromosomes. 22 of the 23 is autosomes. 1 is sex chromosomes. FEATURES OF MEIOSIS1. Cell division which occurs in gonads in “sex cells” (ovaries & sperm)2. Results in 4 daughter cells 3. Daughter cells contain half the DNA (or number of chromosomes) of parent cells. 23 chromosomes.Cellular AdaptationsMany 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 unfavorable conditions. Examples:1. hypertrophy: increase in the size of cells.2. hyperplasia: increase (increased number) in mitotic activity. (not always good)3. atrophy: decrease in size of cells4. metaplasia: changes in cell response to disease or chronic irritation which results in the transformation of the cell into a different cell type. Cell transforms itself due to irritation. (precancerous stage)5. neoplasm: “new cell mass” rapid multiplication. benign: good, not harmful.malignant: bad,