Zoology 100 Prelab Notes

ZOOLOGY 100 PreLab Notes MITOSIS Mitosis: nuclear division (division of the chromosomes) Cytokinesis: division of the cytoplasm Cell division: division of the cell (includes both nuclear division and division of the cytoplasm) Cell life cycle: from the time the cell is first formed until it divides again Interphase: Time when the cell is not dividing, but carrying out other functions. G1: Growth phase: cell enlarges, organelles double in number; cells w/c do not divide stay in this stage for their entire life span S: Synthesis of DNA – cell duplicates it’s genetic material in preparation for mitosis G2: Final preparation for mitosis, division of centrioles; amount of cytoplasm and organelles increase in preparation for mitosis Prophase: mitotic spindle begins to form, chromosomes condense (become visible) Metaphase: chromosomes align along the equator of the cell Anaphase: chromosomes split and sister chromatids (now chromosomes) move to opposite poles Telophase: chromosomes are at the ends of the cell, cleavage furrow is visible Cleavage Furrow (animals) or Cell Plate (plants): indicates cytokenesis, cell membrane begins to pinch inward Contractile ring: formed by microtubules which contract at the middle of the cell splitting them in two. Daughter cells: Two newly formed cells, genetically identical

The cell cycle

The cell cycles in different cells Cell type

Cell cycle / hours

Bean root tip

19.3

Mouse fibroblast

22

Chinese hamster fibroblast

11

Mouse small intestine epithelium

17

Mouse oesophagus epithelium

181

Mitosis process of forming (generally) identical daughter cells by replicating and dividing the original chromosomes, in effect making a cellular xerox. - deals only with the segregation of the chromosomes and organelles into daughter cells. Structure of a eukaryotic chromosome (condensed chromatin = DNA + histone protein)

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DNA "packaged" in the form of Chromosomes Chromosomes are composed of Chromatin • Made of DNA Strands • Also contain Histones - Proteins the DNA is wrapped around Eukaryotes have more than 1 chromosome (humans have 23 pairs)

Structure and main features of a spindle apparatus (microtubules that pull the chromosomes into each cell)

The microtubules have the 9+2 arrangement. Animal cells (except for a group of worms known as nematodes) have a centriole. Plants and most other eukaryotic organisms lack centrioles. Prokaryotes, of course, lack spindles and centrioles; the cell membrane assumes this function when it pulls the by-then replicated chromosomes apart during binary fission. Cells that contain centrioles also have a series of smaller microtubules, the aster, that extend from the centrioles to the cell membrane; serve as a brace for the functioning of the spindle fibers.

Interphase

Prophase

Cell Replicates its DNA/Chromosomes in preparation of upcoming division

1. Chromosomes Shorten and become visible.Nuclear envelope disappears 2. Centrioles begin to migrate to opposite poles of the cell 3. Spindle & Astral Fibers begin to form

Metaphase

1. Chromosomes line up along center of cell along the Metaphase Plate 2. Chromosomes attach to spindle fibers 3. Spindle and astral fibers now clearly visible.

Anaphase

1. Centromeres break up separating chromosome copies Chromosomes are pulled apart to opposite sides of cell 2. Spindle & astral fibers begin to break down

Telophase

Cytokenesis

1. Nuclear envelope forms around both sets of chromosomes 2. DNA uncoils 3. Spindle & astral fibers completely disappear

1. Happens with most (but not all) cells. 2. Cytoplasm & organelles move (mostly equally) to either side of the cell. 3. Cell Membrane "pinches" to form 2 separate cells