1Cell Division IB Topic 2.5 Chapter 12 Campbell New cells arise by division of existing cells .
2OverviewMulticellular organisms begin life as a single cell which grows and dividesIt is important that division of a nucleus produces two new cells (daughter cells) that contain identical sets of chromosomesAchieved by mitosis
3The cell division cycle The cycle of growth and division of a cellSee Fig in textThree main stages1. interphase2. division of the nucleus by mitosis3. cytokinesis (cell division)
4Interphase Longest part of the cell cycle Not resting!! Consists of three phases:1. G1: new organelles formed, growth2. S: cell copies all genetic material (duplicate)3. G2: more growth
5MitosisDivision of a eukaryotic nucleus into two genetically identical nuclei.4 phases (PMAT)2 copies of each chromosome are neededEach chromosome initially consists of a single DNA molecule; this needs to be replicatedTwo identical DNA molecules called sister chromatids (see next slide)
6Prophase Chromosomes become visible as long threads They shorten and thicken by supercoilingFigure 12.3 in textbookOnly at the end of prophase is it possible to see the two chromatids held together at the centromereNuclear membrane breaks downSpindle microtubles are growing
7Metaphase Centrioles move to opposite ends of the cell (poles) Spindle microtubules form and attach to the centromeres of each pair of chromatidsChromosomes are moved to the equator of the cell
8Anaphase Centromeres divide Spindle fibers shorten Chromatids are pulled by their centromeres to opposite polesOnce separated, the chromatids are referred to as chromosomes
9TelophaseNuclear envelope (or membrane) reforms around both groups of chromosomesChromosomes decondense by uncoiling, becoming chromatin again
10Cytokinesis Division of the cytoplasm Cell organelles are evenly distributed between cellsPinching of cytoplasm (cleavage) in halfTwo daughter cells enter interphase again
12The significance of mitosis Daughter cells produced by mitosis have a set of chromosomes identical to each other and to the parent from which they are fromThis occurs because:Exact copy of each chromosome is madeChromatids remain attached during metaphaseCentromeres divideNew nucleiDivision of cytoplasm
13The significance of mitosis (cont.) Growth and development of an embryoRepair of damage or worn out cellsGrowth, development, and repairAsexual reproductionWhy is mitosis critical for items stated above?
14Cancer …Cells divide by mitosis repeatedly without control or regulation, forming a tumorBenign vs. malignantMetastasizeCaused by damage to DNA of chromosomes different types of mistakes, which explain why cancer is not one single diseaseEnvironmental, genetic, and viral influence
16Test yourselfIn each of the following combinations of words or phrases, one word or phrase does not belong. Identify which one it is and explain your answer.1. spindle microtubule formation, replication, growth2. spindle microtubule formation, supercoiling of chromosomes, attachment of microtubules to centromeres3. maintenance, repair, formation of gametes