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The Cell Cycle 1 Cell Division • All cells are derived from preexisting cells • Eukaryote cells divide to make cells for growth and to replace damaged or old cells • Prokaryote cells divide to reproduce 2 Eukaryotic Chromosomes • Human body cells have 46 chromosomes or 23 matching pairs • Each chromosome is composed of a single, tightly coiled DNA molecule 3 Chromosomes in Dividing Cells • Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids 4 Karyotype • A picture of the chromosomes from a human cell arranged in pairs by size • First 22 pairs are called autosomes • Last pair are the sex chromosomes • XX female or XY male 5 Cell Reproduction 6 Types of Cell Reproduction • Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells • Examples: Mitosis & binary fission 7 • Sexual reproduction involves joining two cells (egg & sperm). • Example: Meiosis • Fertilization involves joining of egg & sperm to make a new cell (zygote) 8 Cell Division in Prokaryotes 9 Cell Division in Prokaryotes • Prokaryotes such as bacteria divide into 2 Parent cell identical cells by the process of binary fission Chromosome replicates Cell splits 2 identical daughter cells 10 The Cell Cycle 11 Five Phases of the Cell Cycle 1. G1 - primary growth phase 2. S – synthesis; DNA replicated 3. G2 - secondary growth phase collectively these 3 stages are called interphase 4. M - mitosis 5. C - cytokinesis 12 Interphase 13 Interphase - G1 Stage • 1st growth stage after cell division • Cells mature by making more cytoplasm & organelles • Do all the work of being a cell in this stage 14 Interphase – S Stage • Synthesis stage • DNA is copied or replicated Two identical copies of DNA Original DNA 15 Interphase – G2 Stage • 2nd Growth Stage • Occurs after DNA has been copied • All cell structures needed for division are made (EX: cell organelles & centrioles) 16 The Cell Cycle DNA Copied Cells Mature Daughter Cells Cells prepare for Division Cell Divides into Identical cells 17 Mitosis 18 Mitosis • Division of the nucleus • Only occurs in eukaryotes • Doesn’t occur in brain or muscle cells 19 Four Mitotic Stages 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase 20 Prophase • Chromatin in nucleus condenses to form visible chromosomes • Nuclear membrane & nucleolus are broken down • Centrioles move in animal cells 21 22 Metaphase • Chromosomes move to the center of the cell • Chromosomes are now lined up at the equator Equator of Cell Pole of the Cell 23 Metaphase 24 Anaphase • Occurs rapidly • Sister chromatids are pulled apart to opposite poles 25 Anaphase 26 Telophase • Sister chromatids are at opposite poles • Nuclear envelope forms around each set of sister chromatids • Nucleolus reappears 27 28 Cytokinesis • Means division of the cytoplasm • 1 Cell two identical cells • In plant cells; cell plate forms at the equator to divide cell • In animal cells; cleavage furrow forms to split cell • Chromosome structures dissolve into chromatin 29 Cytokinesis Cleavage furrow in animal cell Cell plate in plant cell 30 Review of Mitosis 31 Eukaryotic Cell Division • Used for growth and repair • Produce two new cells identical to the original cell • Cells are diploid (2n) Prophase Metaphase Chromosomes during Metaphase of mitosis Anaphase Telophase Cytokinesis 32 Locate the Four Mitotic Stages in Plants Anaphase Telophase Metaphase Prophase 33 anaphase prophase metaphase telophase 34 Uncontrolled Mitosis • If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors • Oncogenes - special proteins that increase the chance that a normal cell develops into a tumor cell Cancer cells 35