Bilgy Mitsis and Meisis Lecture Ntes Name Per Learning Gals Quiz #6: December 6th Describe what happens during interphase Identify steps f mitsis/meisis by picture and functin Explain the diseases that ccur when mitsis and meisis g wrng, such as cancer and nndisjunctin Cell Reprductin The life-cycle f the cell is brken int tw sectins: Interphase and Mitsis In interphase, the cell is living its life and perfrming it s nrmal functins. In mitsis, the cell is dividing and creating a daughter cell. At the end f mitsis are tw 100% identical daughter cells The parent n lnger exists Interphase Interphase is the majrity f a cell s life Interphase is three separate stages During the first stage the cell has just been brn. It is grwing and develping prteins which will build the rganelles in the cell During the secnd stage, the cell cpies all f it s DNA (which it will pass t it s daughter cell) During the third stage, the cell perfrms its necessary functins and prepares fr mitsis First Stage f Mitsis Prphase During prphase, the nucleus and nuclear envelpe seem t disappear What is the chrmatin inside the nucleus? (The DNA f the cell) The chrmatin cils up int unique structures called chrmsmes Each chrmsme is attached t its identical cpy f DNA made during interphase, and held tgether by a centrmere Each rganism has chrmsmes f specific shapes and shades Secnd Stage f Mitsis Metaphase In metaphase, the centrmeres f the chrmsmes line up in the center f the cell and attach t spindle fibers Spindle are cytskeletn that are shaped like a ftball The spindle are attached t an rganelle called a centrile The centriles are lcated where the tw daughter cells will eventually frm Each chrmsme lines up in the very center f the cell
Each chrmsme is attached t tw spindle fibers, which will pull the chrmatids t each centrile Third Stage f Mitsis Anaphase In anaphase, the centrmeres split and each identical chrmatid begins t mve t ne f the centriles The chrmatids reach each centrile by walking alng the spindle fibers Furth Stage f Mitsis Telphase In telphase, chrmatids have reached each centrile. The nucleus and nuclear envelpe begin t reappear A new membrane begins t frm and the tw daughter cells becme visible Cytkinesis The last step, which is separate frm the rest f mitsis, is cytkinesis. The tw daughter cells have frmed, but they are still attached t each ther like Siamese twins In animal cells, the tw cells get pinched by the plasma membrane until the tw cells are frced apart In plant cells, the cell wall and the plasma membrane has t be built like a brick wall Apptsis A cell can nly underg s many divisins befre it becmes t risky t reprduce Apptsis is als knwn as prgrammed cell death, because the cell will underg reactins t cause its wn destructin First, the DNA will fragment int pieces and all envelpes and membranes will blister Then, enzymes that have been drmant in the cell since the beginning f interphase first divisin are activated These enzymes destry the rganelles and membrane f the cells and depsit the cell parts int the bld stream fr recycling Cancer Cancer is a disrder that disrupts the prcess f cell reprductin Carcingenesis (develpment f cancer) is gradual and can ccur fr years befre a cell becmes cancerus Sme f the fllwing are characteristics that identify a cancerus cell frm nn-cancerus 1. N differentiatin. Cancerus cells have lst functin. They are simply excess tissue. 2. N cntact inhibitin. Nrmal cells d nt add press against neighbring cells. Cancerus cells expand n matter hw much rm they have, causing neighbring cells stress 3. Frmatin f tumrs Cancer cells pile n tp f each ther, cnstantly dividing withut end. They never underg apptsis 4. Cancer cells invade
Cancer can prduce enzymes that seep int the bld stream and invade ther cells, causing the cancer t spread Why des cancer spread? Smetimes cancer is benign which means yur bdy lcated the cancer and cntained it inside a capsule s it can t spread frm ne cell t the next. Even this is rare. Yu and I get cancer all the time. Our bdy fights it ff and we never ntice. If a tumr des grw, it typically damages the capillaries between the cell and the bld vessels, s the cell can t receive any nutrients. Yu d think this wuld kill the cancer In rder t survive, the cancer cell has learned t either spread its prteins t ther cells (metastasizing) r rebuild new bld vessels int the tumr (angigenesis). Meisis Back t genetics Hw d yu end up with nly ne allele fr each gene frm yur parents? The sex cells f yur bdy (eggs r sperm, fr us) have a prcess that ensures which alleles ffspring receive are cmpletely randm. Their divisin is different than every ther cell in yur bdy The divisin f gametes in rganisms is called meisis Hmlgus Chrmsmes Hmlgus Chrmsmes are tw similar chrmsmes They are similar because they cntain the same GENES but nt necessarily the same ALLELES (versins f a gene). Humans have 23 pairs f hmlgus chrmsmes fr a ttal f 46 chrmsmes. We get ne chrmsme f each pair frm ur mm and ne chrmsme frm ur dad Diplid vs Haplid Mst cells in ur bdy are diplid (2n), meaning they have tw sets f each chrmsme A set frm mm and a set frm dad. The gametes in ur bdy, hwever, are haplid (n), meaning they have nly ne set f each chrmsme **Tw haplid gametes fertilize t prduce ne diplid zygte** Meisis is the prcess f creating these haplid gametes. Meisis I Meisis is brken int tw sectins: meisis I and meisis II At the start f meisis there is ne diplid (2n) cell By the end f meisis there will be fur haplid (n) cells These fur haplid cells will be the gametes fr the rganism Prphase I Prphase I lks like prphase, fr the mst part Organelles disappear, chrmsmes appear One difference thugh is a prcess called crssing ver
Crssing ver is when hmlgus chrmsmes actually trade sectins f chrmsmes Why wuld cells d this? Increases randmness f which alleles are fund n each chrmsme In prphase I the rganelles disappear, the chrmsmes fr each cell appear, and each pair f hmlgus chrmsmes underges crssing ver Metaphase I Just like in mitsis metaphase, the chrmsmes line up in the center f the cell in metaphase I f meisis. One difference: Each hmlgus chrmsme lines up next t each ther in the cell Anaphase I In anaphase I, instead f chrmatids separating as in mitsis, the hmlgus chrmsme pairs separate frm each ther Whle chrmsmes mve t each centrile This step ensures each gamete will hld nly ne cpy f each chrmsme Telphase I Unlike in mitsis, the cell will nt underg a full divisin Instead, a small membrane will be built t ensure the chrmsmes d nt g between each new cell The cell is nw ready t enter Meisis II Meisis II (Similar t Mitsis) Prphase II Chrmsmes appear and nuclear envelpes disappear again Metaphase II Chrmsmes line up at the center f the cell at the metaphase plate Anaphase II Individual chrmatids separate and mve tward separate centriles Telphase II Cell parts refrm, and cytkinesis ccurs Fur new daughter cells have been prduced Genetic Variatin Hw des meisis accunt fr the randmness f which gene the ffspring will receive? In Prphase I, crssing ver mixes which genes are fund n which chrmsme In Anaphase I, separating chrmsmes ensures each cell will nly receive 1 allele/gene In Meisis II, the separatin f chrmsmes int chrmatids ensures each cell nly has ½ f the necessary DNA fr an rganism This will have t mix with the DNA f the ther parent, further adding t the randmness Because f this, can yu guess the number f pssible genetic cmbinatins yu can have? Nndisjunctin Nndisjuctin is when hmlgus chrmsmes fail t prperly separate
Nndisjunctin ccurs if the hmlgus chrmsmes r chrmatids d nt separate. The results can be gametes with an extra set f chrmsmes r a missing set. Smetimes the gametes can still fertilize. Smetimes they cannt. If they can, hwever, the resulting zygte will have t many r t few chrmsmes. Trismy 21 An extra #21 chrmsme Result: Dwn Syndrme XXY The male has an extra X chrmsme Result: Klinefelter s syndrme XO The female is missing an extra sex chrmsme Result: Turner s Syndrme