Cell Division Part 1

A Generalized Cell (b) Animal cell Golgi body Nuclear envelope Chromosomal DNA Nucleus Nucleolus Polyribosomes Ribosome Rough ER Cytoplasm Membrane protein Plasma membrane Smooth ER Mitochondrion Centrioles Microtubules Microfilaments Lysosome (b) Animal cell

The Cell Cycle Synthesis Gap 1 Gap 2 DNA Synthesis Growth Interphase S Synthesis G1 G2 Gap 1 M Gap 2 Mitosis Cytokinesis Prophase Telophase Anaphase Growth Gene expression Differentiation Metaphase Prometaphase Two daughter cells Gene expression Quality control Actual division process

Three Little Words Geneticist Need to Hear… Homolog, Loci, Allele Gene loci (location) Unreplicated chromosome pair A b c Homologous pair of chromo- somes A B c Genotype: AA Bb cc Homozygous for the dominant allele Heterozygous Homozygous for the recessive allele

Replicated Chromosome Pair of sister chromatids Centromere (DNA that is hidden beneath the kinetochore proteins) Kinetochore proteins One chromatid (dark blue) One chromatid (light blue) (a) (b)

Chromatids, Chromosomes… What the… At the end of S phase, a cell has twice as many chromatids as there were chromosomes in G1 phase i.e. - human cell 46 chromosomes in G1 phase 46 pairs of sister chromatids in G2 phase chromosome is therefore a relative term In G1, anaphase, & telophase it refers to the equivalent of one chromatid In G2, prophase, & metaphase, it refers to a pair of sister chromatids

Interphase Chromosomes are decondensed chromosomes replicate Two centrosomes, each with centriole pairs Nuclear membrane Chromosomes are decondensed chromosomes replicate The centrosome divides Chromosomes

Prophase Nuclear envelope dissociates Microtubules forming mitotic spindle Sister chromatids Nuclear envelope dissociates Centrosomes move to opposite poles mitotic spindle apparatus forms Centromere

(d) METAPHASE Astral microtubule Metaphase plate Polar microtubule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Astral microtubule Metaphase plate Polar microtubule Kinetochore proteins attached to centromere Kinetochore microtubule (d) METAPHASE

Spindle Apparatus Composed of microtubules originated from centrioles Microtubules are formed polymerization of tubulin proteins 3 types of spindle microtubules Aster microtubules Important for positioning of the spindle apparatus Polar microtubules Help to “push” the poles away from each other Kinetochore microtubules Attach to kinetochore , at the centromere

Kinetochore Spindle Fibers Figure 3.8

Spindle fibers bind kinetochores Prometaphase Nuclear membrane fragmenting Spindle fibers bind kinetochores The two kinetochores on a pair of sister chromatids are attached to kinetochore MTs from opposite poles Mitotic spindle Spindle pole

Metaphase Astral microtubule Pairs of sister chromatids align themselves at the metaphase plate Metaphase plate Polar microtubule Kinetochore proteins attached to centromere Kinetochore microtubule

Anaphase Centromeres separate Chromosomes Centromeres separate Each chromatid, is linked to only one pole As anaphase proceeds Kinetochore MTs shorten Chromosomes move to opposite poles Polar MTs lengthen Poles themselves move further away from each other

Telophase & Cytokinesis Chromosomes reach poles & decondense Nuclear membrane reforms Quickly followed by cytokinesis In animals Formation of a cleavage furrow In plants Formation of a cell plate

Some Key Points Mitosis ultimately produces two daughter cells genetically identical to the mother cell Barring rare mutations Processes requireing mitotic cell division Development of multicellularity Organismal growth Wound repair Tissue regeneration