1.6 Cell Division The Cell Cycle - Describes the life of a cell. Includes 2 stages: 1) - Interphase the growth and replication (of DNA) stage of the cell when the cell carries out its regular functions as a cell consists of the GI, S, and G2 phases 2) Cell Division - When the cell gets too big, it needs to divide into 2 new cells to become more efficient and maximize its surface area to volume ratio. - Allows for asexual reproduction, growth of the organism, and the replacement of damaged cells - Made of 2 stages a) MITOSIS – the division of nuclear materials (chromosomes) o Consists of 4 stages: prophase, metaphase, anaphase, telophase b) CYTOKINESIS – the division of the cytoplasm and organelles to create 2 new daughter cells DNA - The molecule of heredity for most cells, found within the nucleus It contains genes, which are instructions on how to make proteins that make you who you are During interphase, DNA is found in the form of chromatin CHROMATIN – tangled strands of DNA and proteins Early in mitosis, the chromatin condenses to form chromosomes Single Stranded Chromosome / Chromatid Double Stranded Chromosome Mitosis Terms Sister Chromatids: the identical chromosome strands that comprise a double stranded chromosome Centromere: the region of the chromosome where 2 sister chromatids join Centrioles: a pair of cylindrical cell structures made of protein that will organize the mitotic spindle. Mitotic Spindle (Spindle Apparatus): made of hundreds of microtubules (proteins) that will attach to the centromere of chromosomes and align them during mitosis. MITOSIS and CELL DIVISION PHASE INTERPHASE - - PROPHASE - - MITOSIS - METAPHASE - WHAT HAPPENS The cell grows Prepares for cell division by duplicating its genetic material (DNA) DNA found in the form of chromatin The chromatin shortens and thickens into double stranded chromosomes The nuclear membrane disintegrates centrioles move to opposite poles of the cell Spindle fibers develop and attach to centromeres of chromosomes The spindle fibers line up the double stranded chromosomes in single file along the equator of the cell, metaphase plate. DIAGRAM ANAPHASE - - TELOPHASE - - CYTOKINESIS - - - The spindle fibers pull on the centromeres of the chromosomes separating the sister chromatids of each double stranded chromosomes. Each single strand is pulled to an opposite pole of the cell The chromatids reach the opposite poles of the cell The spindle detaches and new nuclear membranes form around the chromatids Cytokinesis begins even before telophase completes with the formation of a cleavage furrow (indentation of the cell membrane). The cell membrane pinches in to divide the original parent cell in 2 and create 2 new daughter cells Each daughter cell will have the same number of chromosomes as the original parent cell. The chromosomes recondense to form chromatin and the cell cycle begins again with interphase. Cytokinesis in Plant Cells - During telophase, membrane-bound vesicles made from the Golgi Apparatus move to the center of the cell and fuse to form a cell plate - Eventually, the growing cell plate fuses with the existing plasma membrane producing 2 daughter cells with their own plasma membrane - A new cell wall will form between the 2 membranes of the cell plate. Control of the Cell Cycle with Cyclins Cyclins: - Discovered by R. Timothy Hunt in 1982 while studying the cell cycle in sea urchins. - a family of proteins that control the progression of cells through the cell cycle - they bind to enzymes called cyclin dependent kinases (Cdk) activating them - activated Cdk will activate other proteins by phosphorylation (attaching a phosphate group to the proteins) - these phosphorylated proteins can now perform various functions initiating events in the cell cycle. • • • • Cyclin D triggers cells to move from G phase to S phase of interphase Cyclin E prepares the cell for DNA replication in the S phase Cyclin A activates DNA replication inside the nucleus Cyclin B promotes the assembly of the mitotic spindle CANCER Cancer: Disorder in which some of the body's cells lose the ability to control their growth. Tumor: A mass of cells produced by repeated, uncontrolled cell division. Tumors can occur in any organ. Some tumors grow large and spread to other parts of the body (metastasis). The diseases caused by the growth of tumors is known as cancer. Tumors can be benign (harmless) or malignant (ones that can spread) Oncogene: a gene that has the potential to cause cancer. In tumor cells they are mutated or expressed at high levels. Carcinogens/Mutagen (a substance that increases the chance of a mutation leading to cancer) • • • Treatments: • • • Radiation (gamma, UV, x-ray etc.) Chemicals (textile dyes, paints and inks) Viruses (hepititis B and C and HPV) Surgery (the physical removal of a tumor) Radiation (a radiation beam is directed at mutated cells to destroy them) Chemotherapy (medications that target rapidly dividing cells) Cancer & Smoking • There is a strong correlation between smoking and cancer • Women smokers are 25.7 times more likely than women who never smoked to develop lung cancer. For men smokers, it’s 25 times the risk of men who never smoked. (Source: US Surgeon General Report 2014) • Besides lung cancer, tobacco use also increases the risk for cancers of the mouth, lips, nose and sinuses, larynx (voice box), pharynx (throat), esophagus (swallowing tube), stomach, pancreas, kidney, bladder, uterus, cervix, colon/rectum, ovary (mucinous), and acute myeloid leukemia. (Source: Cancer Facts & Figures 2014) Mitotic Index - A way to measure the rate of proliferation (growth) Mitotic Index = # of cells in Mitosis Total # of cells 1.6 Cell Division – Homework Questions 1) Identify the stages of mitosis and cell division seen in the following micrograph. DATA BASE QUESTION 2. One of the largest ever studies of the effect of smoking on health involved 34, 439 male British doctors. Information was collected on how much they smoked from 1951 to 2001 and the cause of death was recorded for each of the doctors who died during this period. The table shows some of the results. Type of disease Non-smoker 107 1037 8 1-14 cigarettes per day 237 1447 11 15-24 cigarettes per day 310 1671 33 >25 cigarettes per day 471 1938 34 Respiratory Circulatory Stomach and duodenal ulcers Cirrhosis of the liver Parkinson’s 6 13 22 68 20 22 6 18 a. Deduce whether there is a positive correlation between smoking and the mortality rate due to all types of disease. b. Using the data in the table, discuss whether the threat to health from smoking is greater with respiratory or with circulatory c. Discuss whether the data suggests that smoking a small number of cigarettes is safe. d. Discuss whether the data proves that smoking is a cause of cirrhosis of the liver e. The table does not include deaths due to cancer. The survey showed that seven types of cancer are linked with smoking. Discuss three cancers you would expect smoking to cause.
