The Cell Cycle CHAPTER 12
The Key Roles of Cell Division cell division = reproduction of cells All cells come from pre-exisiting cells Omnis cellula e cellula
Unicellular organisms division of 1 cell reproduces organism Binary fission
Multicellular organisms Why cells reproduce Development/Growth Replacement Repair
100 µm 200 µm 20 µm (a) Reproduction (b) Growth and development (c) Tissue renewal
Cellular Organization of Genetic Material chromosome = strand of DNA 2 sets of 23 chromosomes in humans = 46 genome = All DNA in a cell 20 µm
Somatic cells= body cells (2 trillion in adult) 2sets of chromosomes (pairs= diploid) Produced by mitosis - 1 diploid cell 2 identical diploid cells Gametes sperm and eggs have 1 set = haploid Produced by meiosis 1 diploid cell 4 unique cells Occurs in?
Gametes
Identical cells Diploid Unique cells Haploid
Concept check 1. start with a fertilized egg 5 cell divisions produce how an embryo of cells 2. a chicken has 78 chromosomes in a somatic cell. How many chromosomes in a chicken sperm?
The cell cycle = time from new cell to when it divides Interphase 90% of time Mitosis 4o min G 1 S (DNA synthesis) G 2
Cell Division Mitosis = division of the nucleus Cytokinesis = division of cytoplasm
INTERPHASE G1 phase cell grows, gets ready S phase DNA replicates G2 phase cell grows, gets ready G 1 S (DNA synthesis) G 2
Signs of interphase?
S phase of Interphase Chromosomes (DNA) replicate Sister chromatids = 2 Centromere = constricted region
0.5 µm Chromosomes DNA molecules Chromosome arm Centromere Chromosome duplication (including DNA synthesis) Sister chromatids Separation of sister chromatids Centromere Sister chromatids
MITOSIS video Prophase (Prometaphase) Metaphase Anaphase Telophase Cytokinesis by late telophase
I. Prophase Chromosomes condense Mitotic spindle forms from centrioles Nuclear membrane breaks apart
The mitotic spindle (formation begins in prophase) Prophase G 2 of Interphase Centrosomes Aster
Prophase
II. Prometaphase Spindle microtubules attach to kinetochores of chromosomes Chromosomes pulled towards center of cell
III. Metaphase chromosomes (sister chromatids) line up at the metaphase plate midway between spindle s two poles
Aster Centrosome Microtubules Chromosomes Sister chromatids Metaphase plate Kinetochores Centrosome 1 µm Overlapping nonkinetochore microtubules Kinetochore microtubules 0.5 µm
G 2 of Interphase Prophase Prometaphase G 2 of Interphase Prophase Prometaphase Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Nonkinetochore microtubules Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore Kinetochore microtubule
Metaphase Anaphase Telophase and Cytokinesis Metaphase Anaphase Telophase and Cytokinesis Metaphase plate Cleavage furrow Nucleolus forming Spindle Centrosome at one spindle pole Daughter chromosomes Nuclear envelope forming
IV. Anaphase sister chromatids separate microtubules shorten move chromosomes toward opposite ends of cell
V. Telophase Identical nuclei form in each cell Chromosomes less condensed (they become threadlike again)
Division of cytoplasm animal cells cleavage furrow Cytokinesis plant cells cell plate
Cleavage furrow 100 µm Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM)
Vesicles forming cell plate Wall of parent cell Cell plate New cell wall 1 µm Daughter cells (b) Cell plate formation in a plant cell (TEM)
Nucleus Nucleolus Chromatin condensing 1 Prophase
Chromosomes 2 Prometaphase
3 Metaphase
4 Anaphase
Cell plate 10 µm 5 Telophase
The cell cycle is regulated by a molecular controls Short length ex. skin cell Longer length ex. Neurons Specific signal molecules in cytoplasm
Application: Cancer Mutation in cell cycle genes Breast cancer cells dividing