Cellular Division 1 Cell Division All cells are

Cellular Division 1

Cell Division üAll cells are derived from pre- existing cells üNew cells are produced for growth and to replace damaged or old cells üDiffers in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals) 2

Keeping Cells Identical The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules 3

DNA Replication üDNA must be copied or replicated before cell division üEach new cell will then have identical copy the DNA Original DNA strand Two new, identical DNA strands an of 4

Identical Daughter Cells Two identical daughter cells Parent Cell 5

Chromosomes 6

Prokaryotic Chromosome ü The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane 7

Eukaryotic Chromosomes üAll eukaryotic information in cells store genetic chromosomes ü Most eukaryotes have between 10 and 50 chromosomes in their body cells ü Human body cells have 46 chromosomes or 23 identical pairs 8

Eukaryotic Chromosomes üEach chromosome is composed of a single, tightly coiled DNA molecule üChromosomes can’t be seen when cells aren’t dividing and are called chromatin 9

Compacting DNA into Chromosomes üDNA is tightly coiled around proteins called histones 10

Chromosomes in Dividing Cells üDuplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids 11

Karyotype ü A picture of the chromosomes from a human cell arranged in pairs by size ü First 22 pairs are called autosomes ü Last pair are the sex chromosomes ü XX female or XY male 12

Boy or Girl? The Y Chromosome Decides Y - Chromosome X - Chromosome 13

Cell Reproduction 14

Types of Cell Reproduction üAsexual reproduction involves a single cell dividing to make 2 new, identical daughter cells üMitosis & binary fission are examples of asexual reproduction üSexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells üMeiosis is an example 15

Cell Division in Prokaryotes 16

Cell Division in Prokaryotes ü Prokaryotes such as bacteria divide into 2 Parent cell identical cells by the process of binary fission Chromosome ü Single chromosome relicates makes a copy of itself ü Cell wall forms Cell splits between the chromosomes dividing the cell 2 identical daughter cells 17

Prokaryotic Cell Undergoing Binary Fission 18

Animation of Binary Fission 19

The Cell Cycle 20

Five Phases of the Cell Cycle üG 1 - primary growth phase üS – synthesis; DNA replicated üG 2 - secondary growth phase collectively these 3 stages are called interphase üM - mitosis üC - cytokinesis 21

Cell Cycle 22

Interphase - G 1 Stage ü 1 st growth stage after cell division üCells mature by making more cytoplasm & organelles üCell carries on its normal metabolic activities 23

Interphase – S Stage üSynthesis stage üDNA is copied or replicated Two identical copies of DNA Original DNA 24

Interphase – G 2 Stage ü 2 nd Growth Stage üOccurs after DNA has been copied üAll cell structures needed for division are made (e. g. centrioles) üBoth organelles & proteins are synthesized 25

What’s Happening in Interphase? What the cell looks like Animal Cell What’s occurring 26

Sketch the Cell Cycle DNA Copied Cells Mature Daughter Cells prepare for Division Cell Divides into Identical cells 27

Mitosis 28

Mitosis üDivision of the nucleus üAlso called karyokinesis üOnly occurs in eukaryotes üHas four stages üDoesn’t occur in some cells such as brain cells 29

Four Mitotic Stages üProphase üMetaphase üAnaphase üTelophase 30

Early Prophase üChromatin in nucleus condenses to form visible chromosomes üMitotic spindle forms from fibers in cytoskeleton or centrioles (animal) Nucleolus Chromosomes Cytoplasm Nuclear Membrane 31

Late Prophase üNuclear membrane & nucleolus are broken down üChromosomes continue condensing & are clearly visible üSpindle fibers called kinetochores attach to the centromere of each chromosome üSpindle finishes forming between the poles of the cell 32

Late Prophase Chromosomes Nucleus & Nucleolus have disintegrated 33

Spindle Fiber attached to Chromosome Kinetochore Fiber Chromosome 34

Review of Prophase What the cell looks like What’s happening 35

Spindle Fibers üThe mitotic spindle form from the microtubules in plants and centrioles in animal cells üPolar fibers extend from one pole of the cell to the opposite pole üKinetochore fibers extend from the pole to the centromere of the chromosome to which they attach üAsters are short fibers radiating from centrioles 36

Sketch The Spindle 37

Metaphase üChromosomes, attached to the kinetochore fibers, move to the center of the cell üChromosomes are now lined up at the equator Equator of Cell Pole of the Cell 38

Metaphase Asters at the poles Spindle Fibers Chromosomes lined at the Equator 39

Metaphase Aster Chromosomes at Equator 40

Review of Metaphase What the cell looks like What’s occurring 41

Anaphase üOccurs rapidly üSister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers 42

Anaphase Sister Chromatids being separated 43

Anaphase Review What the cell looks like What’s occurring 44

Telophase üSister chromatids at opposite poles üSpindle disassembles üNuclear envelope forms around each set of sister chromatids üNucleolus reappears üCYTOKINESIS occurs üChromosomes reappear as chromatin 45

Comparison of Anaphase & Telophase 46

Cytokinesis üMeans division of the cytoplasm üDivision of cell into two, identical halves called daughter cells üIn plant cells, cell plate forms at the equator to divide cell üIn animal cells, cleavage furrow forms to split cell 47

Cytokinesis Cleavage furrow in animal cell Cell plate in plant cell 48

Mitotic Stages 49

Daughter Cells of Mitosis üHave the same number of chromosomes as each other and as the parent cell from which they were formed üIdentical to each other, but smaller than parent cell üMust grow in size to become mature cells (G 1 of Interphase) 50

Identical Daughter Cells What is the 2 n or diploid number? 2 Chromosome number the same, but cells smaller than parent cell 51

Review of Mitosis 52

Name the Mitotic Stages: Interphase Name this? Prophase Telophase Name this? Metaphase Anaphase 53

Eukaryotic Cell Division ü Used for growth and repair ü Produce two new cells identical to the original cell ü Cells are diploid (2 n) Prophase Metaphase Chromosomes during Metaphase of mitosis Anaphase Telophase Cytokinesis 54

Mitosis Animation Name each stage as you see it occur? 55

Mitosis in Onion Root Tips Do you see any stages of mitosis? 56

Draw & Learn these Stages 57

Draw & Learn these Stages 58

Test Yourself over Mitosis 59

Mitosis Quiz 60

Mitosis Quiz 61

Name the Stages of Mitosis: Early Anaphase Early prophase Metaphase Interphase Late Prophase Late telophase, Mid-Prophase Advanced cytokinesis Early Telophase, Begin cytokinesis Late Anaphase 62

Identify the Stages ? Early, Middle, & Late Prophase ? ? Metaphase Late Prophase Late Anaphase ? ? Telophase ? ? Telophase & Cytokinesis 63

Locate the Four Mitotic Stages in Plants Anaphase Telophase Metaphase Prophase 64

Uncontrolled Mitosis ü If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors ü Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell Cancer cells 65

Meiosis Formation of Gametes (Eggs & Sperm) 66

Facts About Meiosis üPreceded by interphase which includes chromosome replication üTwo meiotic divisions --- Meiosis I and Meiosis II üCalled Reduction- division üOriginal cell is diploid (2 n) üFour daughter cells produced that are monoploid (1 n) 67

Facts About Meiosis üDaughter cells contain half the number of chromosomes as the original cell üProduces gametes (eggs & sperm) üOccurs in the testes in males (Spermatogenesis) üOccurs in the ovaries in females (Oogenesis) 68

More Meiosis Facts ü Start with 46 double stranded chromosomes (2 n) üAfter 1 division - 23 double stranded chromosomes (n) üAfter 2 nd division - 23 single stranded chromosomes (n) ü Occurs in our germ cells that produce gametes 69

Why Do we Need Meiosis? üIt is the fundamental basis of sexual reproduction üTwo haploid (1 n) gametes are brought together through fertilization to form a diploid (2 n) zygote 70

Fertilization – “Putting it all together” 2 n = 6 1 n =3 71

Replication of Chromosomes ü Replication is the process of duplicating a chromosome ü Occurs prior to division ü Replicated copies are called sister chromatids ü Held together at centromere Occurs in Interphase 72

A Replicated Chromosome Gene X Homologs (same genes, different alleles) Sister Chromatids (same genes, same alleles) Homologs separate in meiosis I and therefore different alleles separate. 73

Meiosis Forms Haploid Gametes ü Meiosis must reduce the chromosome number by half ü Fertilization then restores the 2 n number from mom from dad child too much! meiosis reduces genetic content The right number! 74

Meiosis: Two Part Cell Division Sister chromatids separate Homologs separate Meiosis II Diploid Haploid 75

Meiosis I: Reduction Division Nucleus Early Late Prophase I (Chromosome Prophase I number doubled) Spindle fibers Nuclear envelope Metaphase Anaphase Telophase I I I (diploid) 76

Prophase I Early prophase üHomologs pair. üCrossing over occurs. Late prophase üChromosomes condense. üSpindle forms. üNuclear envelope fragments. 77

Tetrads Form in Prophase I Homologous chromosomes (each with sister chromatids) Join to form a TETRAD Called Synapsis 78

Crossing-Over ü Homologous chromosomes in a tetrad cross over each other ü Pieces of chromosomes or genes are exchanged ü Produces Genetic recombination in the offspring 79

Homologous Chromosomes During Crossing-Over 80

Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment 81

Metaphase I Homologous pairs of chromosomes align along the equator of the cell 82

Anaphase I Homologs separate and move to opposite poles. Sister chromatids remain attached at their centromeres. 83

Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two. 84

Meiosis II Gene X Only one homolog of each chromosome is present in the cell Sister chromatids carry identical genetic information. Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene. 85

Meiosis II: Reducing Chromosome Number Prophase Metaphase II Telophase II Anaphase 4 Identical II II haploid cells 86

Prophase II Nuclear envelope fragments. Spindle forms. 87

Metaphase II Chromosomes align along equator of cell. 88

Anaphase II Equator Pole Sister chromatids separate and move to opposite poles. 89

Telophase II Nuclear envelope assembles. Chromosomes decondense. Spindle disappears. Cytokinesis divides cell into two. 90

Results of Meiosis Gametes (egg & sperm) form Four haploid cells with one copy of each chromosome One allele of each gene Different combinations of alleles for different genes along the chromosome 91

Gametogenesis Oogenesis or Spermatogenesis 92

Spermatogenesis ü Occurs in the testes ü Two divisions produce 4 spermatids ü Spermatids mature into sperm ü Men produce about 250, 000 sperm per day 93

Spermatogenesis in the Testes Spermatid 94

Spermatogenesis 95

Oogenesis üOccurs in the ovaries üTwo divisions produce 3 polar bodies that die and 1 egg üPolar bodies die because of unequal division of cytoplasm üImmature egg called oocyte üStarting at puberty, one oocyte matures into an ovum (egg) every 28 days 96

Oogenesis in the Ovaries 97

Oogenesis First polar body may divide (haploid) a Mitosis Oogonium (diploid) X A X Primary oocyte (diploid) X a a Polar bodies die X Meiosis II (if fertilization A occurs) X A X Secondary oocyte (haploid) Ovum (egg) Mature egg A X Second polar body (haploid) 98

Comparing Mitosis and Meiosis 99

Comparison of Divisions Mitosis Number of divisions Number of daughter cells Genetically identical? 1 Meiosis 2 2 4 Yes No Same as parent Half of parent Where Somatic cells Germ cells When Throughout life At sexual maturity Growth and repair Sexual reproduction Chromosome # Role 100

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