By Pn. Aslizah Binti Mohd Aris

 Chromosome morphology and function  The cell cycle and mitosis  Meiosis and gametogenesis

Here “chromosome” and “DNA” are not 100% synonymous

Chromosomes Tightly packaged DNA Found only during cell division DNA is not being used for macromolecule synthesis Chromatin Unwound DNA Found throughout Interphase DNA is being used for macromolecule synthesis

Though chromosomes are “all about” DNA, in fact much this structure consists of protein Form via replication, not by formed chromatids coming together

1. A eukaryotic cell has multiple chromosome, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. 2. Once replicated, a chromosome consists of two sister chromatids connected along their entire lengths by sister chromatidcohesion. Each chromatid contains a copy of the DNA molecule 3. Mechanical processes separate the sister chromatids into two chromosomes and distibute them to two daughter cells. ChromosomesDNA molecules

 A chromatid is a chromatid as long as it is held in association with a sister chromatid at the centromere Chromosome Centromere Chromatid  When two sister chromatids separate (after metaphase) they go from being a single chromosome to being two different chromosomes

Genome = DNA Chromosome = DNA + protein (visible light microscope) Chromatin = DNA + protein (but less than for chromosome) DNA

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers Recall that the centrosome is the center of the microtubule array of a cell

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers Keep in mind that the term centriole is not an exact synonym of centrosome and that centrosome is not a synonym of the term centromere Recall that these consist of microtubules and that a pair makes up a centrosome

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers Responsible for moving chromosomes relative to mitotic spindle

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers These are the portion of the mitotic spindle that is connected to chromosomes during mitosis

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers These are the microtubles that are responsible for separating chromosomes as well as pushing the centrosomes toward opposite ends of cells

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers Microtubules of mitotic spindle that are not connected to the chromosomes but instead responsible for pushing centrosome apart

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers The mitotic spindle as visible through a light microscope

Centromere Centrosome Centriole Kinetochore Kinetochore microtubules Mitotic spindle Nonkinetochore microtubles Spindle apparatus Spindle fibers Bundles of microtubles making up the spindle apparatus; it is the bundling that makes them visible through a light microscope

“G” stands for “Gap”

 Mitosis is conventionally divided into five phases:  Prophase  Prometaphase  Metaphase  Anaphase  Telophase  Cytokinesis is well underway by late telophase BioFlix: Mitosis BioFlix: Mitosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings MITOSIS

Cytokinesis can occur simultaneous to telophase

Nucleus defined Nucleoli present Replicated Centrosomes Asters present DNA duplicated DNA still chromatin

Chromatic condensation Nucleoli disappear Mitotic spindle forms Centrosome separation

Nuclear envelope fragments Microtubules invade nucleus Microtubles interact chromosomes Kinetochores at centromeres Chromosomes jerky movements Nonkinet. microtubule interaction

Centrosomes opposite poles Metaphase plate Chromosomes straddle MP Kinetochores attached KMT Spindle apparatus Brief, static phase

Begins with “sister” separation Chromatids now chromosomes “Sisters” to opposite poles Movement centromere first Non-kinet. microtu. lengthening Further separation of poles

Non-kinet. microtu. lengthening “Sisters” at opposite poles Nuclear env. reformation Reforms from endomembrane Chromosome decondensation Cytokinesis already under way

 In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow  In plant cells, a cell plate forms during cytokinesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cleavage Furrow