CHAPTER 12 The Cell Cycle

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

Why cells reproduce  Development/Growth  Replacement  Repair Multicellular organisms

100 µm200 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

chromatin complex of DNA and protein

Somatic cells= body cells (2 trillion in adult)  two sets 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 only in ?

Identical cells Unique cells Diploid 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?

Human Arabidposis

The cell cycle = time from new cell to when it divides Interphase – 90% of time Mitosis 4o min S (DNA synthesis) MITOTIC (M) PHASE G1G1 G2G2

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 S (DNA synthesis) MITOTIC (M) PHASE G1G1 G2G2 If cycle is 24 hrs, how long each phase?

Signs of interphase?

S phase of Interphase Chromosomes (DNA) replicate Sister chromatids = 2 Centromere = constricted region

0.5 µmChromosomes Chromosome duplication (including DNA synthesis) Chromosome arm Centromere Sister chromatids DNA molecules Separation of sister chromatids Centromere Sister chromatids

 Prophase  Prometaphase  Metaphase  Anaphase  Telophase Cytokinesis by late telophase MITOSIS video video

 Chromosomes condense  Mitotic spindle forms from centrioles  Nuclear membrane breaks apart I. Prophase

The mitotic spindle (formation begins in prophase) Prophase G 2 of Interphase  Aster Centrosomes Aster = radial array of microtubules

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

Microtubules Chromosomes Sister chromatids Aster Metaphase plate Centrosome Kineto- chores Kinetochore microtubules Overlapping nonkinetochore microtubules Centrosome 1 µm 0.5 µm

Prophase Prometaphase G 2 of Interphase PrometaphaseProphase G 2 of Interphase Nonkinetochore microtubules Fragments of nuclear envelope Aster Centromere Early mitotic spindle Chromatin (duplicated) Centrosomes (with centriole pairs) Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule

MetaphaseAnaphase Telophase and Cytokinesis MetaphaseAnaphase Telophase and Cytokinesis Cleavage furrow Nucleolus forming Metaphase plate Centrosome at one spindle pole Spindle Daughter chromosomes Nuclear envelope forming

IV. Anaphase sister chromatids separate microtubules shorten – depolymerize to move chromosomes toward opposite ends of cell

V. Telophase Identical nuclei form at opposite ends of cell Chromosomes less condensed

Cytokinesis Division of cytoplasm animal cells  cleavage furrow plant cells  cell plate

Cleavage furrow 100 µm Daughter cells (a) Cleavage of an animal cell (SEM) Contractile ring of microfilaments

Daughter cells (b) Cell plate formation in a plant cell (TEM) Vesicles forming cell plate Wall of parent cell New cell wallCell plate 1 µm

Nucleus Prophase 1 Nucleolus Chromatin condensing

Prometaphase 2 Chromosomes

Metaphase 3

Anaphase 4

Telophase 5 Cell plate 10 µm

Evolution of Mitosis mitosis is thought to have evolved from binary fission Some protists exhibit cell division intermediate between binary fission and mitosis

The cell cycle is regulated by a molecular controls Short length – ex. skin cell Longer length – ex. Neurons Specific signal molecules in cytoplasm

S G1G1 M checkpoint G2G2 M Control system G 1 checkpoint G 2 checkpoint

Application: Cancer Mutation in cell cycle genes  Breast cancer cells dividing Breast cancer cells dividing