2 Why is Cell Division Important? Unicellular organismsReproduce by cell division increasing the population.100 µm(a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM).Figure 12.2 A
3 Why Do Multicellular Organisms Depend on Cell Division? Development & GrowthRepair (ex: tissue renewal)Maintenance20 µm200 µm(b) Growth and development This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM).(c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM).
4 Cell Division (aka Mitosis) Makes 2 genetically identical daughter cells from 1 parent cellBefore cells divideThey duplicate their genetic material ensures that each daughter cell receives an exact copy of the genetic material, DNA
5 What is the structure of a chromosome? Where in a cell is the genetic material/chromosomes located?NucleusChromatin is an uncoiled mass of DNA and histone proteinsExists in this form the majority of the time!Histones are proteins that help DNAcondenseAs a cell prepares to divide it coilsup/condenses:We call this CHROMOSOMES (condensedDNA)
6 DNA Molecules DNA (in nucleus of eukaryotes) can be in 2 forms Chromatin : DNA is not tightly packed together (loosely coiled)Occurs during interphaseChromosomes : tightly packed together (TIGHTLY coiled)Occurs during mitosis (cell division)
8 Genes Segments of DNA (that make up the chromosome) are called genes A gene is a piece/segment of DNA that stores genetic information
9 What happens to chromosomes during cell division? What needs to be done to a chromosome before it can divide?It must DUPLICATE! (DNA Replication)After duplication each chromosome consists of 2 identically joined copies Sister ChromatidsSister Chromatids are held together by centromeresChromatinChromatidSisterChromatids (condensed, duplicated chromosome)Recall that each chromosome has already been copied (s phase). Thus, the chromosomes look similar to an “X” in which the L and R chromatids are idential DNA double helixes
10 Double Chromosome Structure Kinetochore attaches to spindle fibersSister
11 ChromosomesEvery eukaryotic species has a characteristic, unique # of chromosomes in EACH cell nucleusEx: Humans have 46 chromosomes# of chromosomes does NOT necessarily equal complexity
12 The Cell CycleThe mitotic phase alternates with interphase in the cell cycleInterphasemitosisinterphasemitosis
13 What is Mitosis!?Mitosis is the process where cells divide to produce new cells- Occurs in healing (Ex: if you cut yourself)New cells are also produced as you grow- Ex: Day-to-day life (new skin cells!)ALL eukaryotic organisms produce new cells through mitosis
14 Cell Cycle Consists of 2 broad stages 1. Growing Stage called Interphase2. Cell Division called Mitotic Phase (M Phase)The majority of the cell cycle (90%) is spent in Interphase
15 Phases of the Cell Cycle INTERPHASEG1S (DNA synthesis)G2Cytokinesis MitosisMITOTIC (M) PHASEFigure 12.5
16 Interphase can be divided into subphases G1 phase (GAP 1 phase)cell grows in sizevaries most in length from cell to cellS phase (synthesis phase)DNA is copied (DNA replication)Single DoubleEach chromosome is singleDNA replication occursChromosomes have doubled each consisting of two sister chromatidsG2 phase (GAP 2 phase)More growth and preparation (make proteins) for mitosis
19 Mitotic Phase After Interphase, Mitotic Phase begins Two parts of M Phase:Mitosis (division of the nucleus)2) Cytokinesis (division of the cytoplasm)
20 M PhaseMitosis – the nucleus and duplicated chromosomes divide and create two identical daughter cellsCytokinesis – the process by which the cytoplasm is divided in two.Cytokinesis usually begins before Mitosis is completed.
21 Refresher……. The Cell Cycle: G1 phase: Growth S phase: DNA replication G2 phase: Preparation for cell divisionM phase: Mitosis and Cytokinesis
22 I Passed My Accelerated Tough Class Remember….InterphaseProphaseMetaphaseAnaphaseTelophaseCytokinesisIPMATCI Passed My Accelerated Tough Class
23 Interphase Consists of G1, S, G2 Occurs BEFORE Mitosis begins chromosomeConsists of G1, S, G2Occurs BEFORE Mitosis beginsDuring S phase, the cell copies its DNAChromosomes appear as threadlike coilsMade of Chromatin, a combination of DNA and protein moleculesAs the cell prepares to divide, its chromatin fibers condense, becoming the compact structure we call a chromosome.Chromosomes are copied (# doubles)Condensed, duplicated chromosome
24 InterphaseEach chromosome has now been condensed and duplicated and consists of 2 sister chromatidsThe region where the two chromatids are joined tightly together is called the centromere.
26 Mitosis Continuous pathway (Early, Mid, & Late) Consists of 4 phases and cytokinesisProphaseMetaphaseAnaphaseTelophaseCytokinesis
27 Prophase (X’s) “Pack Together” First phase of Mitosis:Chromatin becomes tightly coiled = chromosomesDNA “packs” togetherSpindle Fibers (made by the centrioles) begins to form in the cytoplasm3. Nuclear envelope breaks downLate: Nucleus and nucleolus disappear
29 Prophase:2. Centrioles moveDNA supercoils into chromosomes
30 Metaphase (X’s) “Meet in the Middle” Second phase of Mitosis:Chromosomes attach to the spindle at the centromeresChromosomes line up in the middle of cellCalled equatorial or metaphase plateSpinder fibers pull and tug chromosomes to line up
33 Anaphase (V’s) “Adios and Away” Third phase of Mitosis:Spindle pulls apart chromosomesSISTER CHROMATIDS separate athe the centromere and begin moving to opposite ends (poles) of the cellEach chromatid is now considered its own chromosome
35 ***Remember that each chromatid has the same DNA so each is now its own chromosome*** Anaphase:
36 Telophase (V’s) “Two New Cells” Fourth phase of Mitosis:Chromosomes reach end of spindleSpindle breaks down (disappear)Cleavage furrow begins to form4. Nuclear membrane begins to reform5. 2 daughter nuclei6. Chromosomes chromatin
38 Cytokinesis “Division of the Cytoplasm” Occurs in Late telophaseIn animal cellsa cleavage furrow forms, which pinches the cell in two.In plant cellsproduce a cell plate at the middle of the cellAt the end of cytokinesis, there are two distinct IDENTICAL daughter cells.
39 Cytokinesis Final Phase of Cell Division/M Phase Cleavage furrow pinches all the way throughResult is two new cells2 cells then enter Mitosis begins again!G1, S, G2 (Interphase)PMAT & CytokinesisEach new cell at the end of mitosis is DIPLOIDhas a full set of chromosomes
40 Cytokinesis: A Closer Look Cleavage furrowContractile ring of microfilamentsDaughter cells100 µm(a) Cleavage of an animal cell (SEM)Figure 12.9 AIn animal cellsCytokinesis occurs by a process known as cleavage, forming a cleavage furrow
41 In plant cells, during cytokinesis A cell plate forms Daughter cells1 µmVesicles forming cell plateWall of patent cellCell plateNew cell wall(b) Cell plate formation in a plant cell (SEM)Figure 12.9 B
42 Figure 12.6 G2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs)Chromatin (duplicated)Early mitotic spindleAsterCentromereFragments of nuclear envelopeKinetochoreNucleolusNuclear envelopePlasma membraneChromosome, consisting of two sister chromatidsKinetochore microtubuleFigure 12.6Nonkinetochore microtubules
43 Figure 12.6 Centrosome at one spindle pole Daughter chromosomes METAPHASEANAPHASETELOPHASE AND CYTOKINESISSpindleMetaphase plateNucleolus formingCleavage furrowNuclear envelope formingFigure 12.6
45 Mitosis in a plant cell Nucleus Chromatine condensing Chromosome 1Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from.Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelop will fragment.Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate.Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their kinetochore microtubles shorten.Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell.2345NucleusNucleolusChromosomeChromatine condensingFigure 12.10
Your consent to our cookies if you continue to use this website.