ZOL 141 1st Edition Lecture 5 Outline of Last Lecture I The Cell II Organelles III Problems with Organelles a Examples Outline of Current Lecture I CELL CYCLE a Interphase b Mitosis c Cytokinesis II Mitosis is Essential to growth III Genetic Diseases Associated with problems of cell division Current Lecture CELL CYCLE Definition sequence from one cell division to the next cell division Three stages 1 Interphase G1 S G2 2 Mitosis produces two genetically identical daughter cells i e nuclear division a Telophase b Anaphase c Metaphase d prophase 3 Cytokinesis cytoplasmic cell division Duplication and distribution of all materials Time between divisions varies from minutes to months or even years Some cells stop dividing such as cardiac cells Assume duplication once per day Interphase G1 G1 Gap 1 growth i e organellses membranes ribosomes made cell increases in size Time frame several hours 9 10 Chromosome One chromatid S synthesis DNA is synthesized chromosomes are duplicated Time frame several hours 9 10 Chromosomes two sister chromatids G2 Gap 2 Preparation for cell division Time frame shorter than G1 and S 4 hours Chromosome two sister chromatids Mitochondria start to grow and divide Spindle fibers begin to assemble Mitosis form of cell division that produces two genetically identical cells Chromosomes have already replicated Early prophase two pairs of centrioles nuclear envelope begins to break down nuclear envelope starts to open up Late prophase chromosomes condense even more centrioles migrate to top and bottom of cell Transition to Metaphase no nucleus DNA dispersed throughout cell spindle fibers begin to attach to centrioles with microtubules Metaphase chromosomes line up in middle of cell equator each chromosome connected to centriole Anaphase movement of chromosomes toward different poles each chromatid separated sister chromatids move to opposite poles ensures that two daughter cells are genetically identical Telophase Nucleus begins to form again in each daughter cell still connected Cytokinesis Daughter cells completely divide from each other Mitosis is Essential for Growth Cells which constantly divide bone marrow produces blood cells skin cells Cells which do not normally divide cardiac muscle cells Cells can divide about 50 times Hayflick limit Adult cells 10 30 times Embryonic stem cells unlimited Genetic Diseases Associated with problems of cell division Progeria o 1 in 4 million newborn o normally new mutation o mutation in gene LMNA responsible for shape of nucleus o affects cell division cells die prematurely o affected individuals die on average by age 13 by hearth attack or stroke Werner Syndrome o 1 in 200000 live birth o mutation in WRN gene o rapid aging no growth spurt in puberty Roberts Syndrome o Most severe o Problems with splitting of centromeres chromosomes do not line up properly o Symptoms short arms and legs facial abnormalities deformations mental impairment possible o Very rare only about 150 individuals known to have had this