Mitosis Notes
1.General
a.Approximately 10 trillion cells in the human body all arose from a single cell by mitosis. E.g., red blood cells are made at the rate of one million per second
b.Cell division is called mitosis. For single celled organisms, mitosis increases the number of individuals; for multi-celled organisms, mitosis adds to growth, differentiation and repair.
c.Mitosis has two basic function
i.Duplicate the cell
ii.Ensure that each daughter cell has a complete copy of the DNA
d.The basic steps are
i.Duplicate the DNA
ii.Divide the chromosomes into two complete sets
iii.Divide the cell into two daughter cells
e.The cell cycle (Fig. 11.5 p. 207C) consists of mitosis (10%) and interphase (90%)
2.Stages of the cell cycle (Fig. 22.6 pp. 536-7N)
a.Interphase
i.Includes all cell activity between mitotic divisions during which the cell is preparing for division. This includes production of cytoplasm and organelles for two daughter cells.
ii.Centrioles are also duplicated.
b.Mitosis
i.Prophase
(1)The chromosomes shorten and thicken
(2)Centrioles move to opposite poles of the cell
(3)Spindle fibers are contructed to extend from the centrioles toward each chromosome
(4)Each chromosome is duplicated and the resulting copies are called sister chromatids. They remain attached to one another at a region called the centromere
(5)The nuclear membrane is dissolved
ii.Metaphase
(1)During late prophase chromatids begin to move toward the cell equator (metaphase plate)
(2)At metaphase the chromatids are aligned at the equator
iii.Anaphase
(1)Chromatids begin to move apart, toward opposite poles
(2)Once separated, the chromatids are again called chromosomes
iv.Telophase
(1)The chromosomes reach opposite poles of the cell
(2)Spindle fibers dissolve
(3)Nuclear membrane reforms at each end of the cell
v.Cytokinesis
(1)The division of cytoplasm after separation of the chromosomes
(2)In plant cells, a new cell wall forms to divide the two daughter cells
(3)In animal cells the cleavage furrow forms as the cell membrane is pinched inward to divide the cell into two daughter cells
Cell Cycle
Cell Cycle: Cell Life Cycle. The repeating sequnce of growth and division through which eukaryotic cells pass each generation.
Stages of Cell Growth
1. G1 phase: primary growth phase. Cell does its 'job'.
2. S phase: DNA replication
3. G2 phase: Chromosome condensation, cell organelle replication
4. M phase: mitosis (nuclear division) (Prophase, metaphase, anaphase, & telophase)
5. C phase: cytokinesis (cytoplasmic division), daughter cells form
Chromosome: DNA and associated proteins (nucleosomes) that help condense chromosome into a smaller area during mitosis.
Sister Chromatids: After replication, the 2 duplicated chromosomes are held together by a centromere. The 2 identical chromosomes are called sister chromatids until they separate in anaphase. The condensation of chromatids makes it easier for the cell to move the sister chromatids around the cell during mitosis.
[Interphase] - Longest stage of cell cycle (The part where it does not divide). (G1, S, G2). Human cells contain 46 chromosomes during the G1 stage of interphase. This is doubled to 92 during the S stage of interphase.
Mitosis - Nuclear Division
Differences in Cell Division Between Animal Cells & Plant Cells
Animal Cells / Plant CellsLate in anaphase, the plasma membrane pulls inward forming a cleavage furrow, which divides the cell in two during telophase. / After anaphase, a new cell wall forms between the two new nuclei to create two cells.
A centriole is found at each pole during mitosis. / No centrioles are found in plant cells.
Uses of Mitosis in Eukaryotic Cells:
a. during growth of the individual.
b. when tissues have been damaged and need to be repaired (as in healing of a cut).
c. to reproduce asexually.
MITOSIS PHASES
Interphase:
Preparation for mitosis (stages G1,S,G2).
Cells grow, chromosomes replicate and condense, organelles replicate. Longest stage
Prophase:
*Chromosomes twist and fold and compact into a smaller area, becoming visible.
Spindle forms from microtubules.
*Nuclear envelope breaks down.
*Centrioles move to poles (no centrioles in plants).
Metaphase:
Sister chromatids align in center of spindle at equator.
Centromeres split (so the chromatids may be pulled apart in anaphase).
Anaphase:
*Spindle fibers contract, pulling sister chromatids to separate poles.
In animal cells, the cells begin to split apart, forming a cleavage furrow as seen above.
*The cleavage furrow is very shallow during anaphase.
In plant cells, the cell wall prevents division of the cytoplasm by a cleavage furrow.
Telophase in Animal Cells:
Spindle fibers finish contracting, sister chromatids now at separate poles.
A nuclear membrane forms around the chromosomes late in telophase.
The chromosomes may disappear late in telophase.
In animal cells, cytokinesis (the actual division of the cell) & a cleavage furrow is now deep into the interior of the cell.
Telophase In Plant Cells:
Spindle fibers finish contracting, sister chromatids now at separate poles.
*Cytokinesis (actual division of the cell) occurs. -- A cell plate (a newly forming cell wall) begins to form across the equator, soon to separate the original cell into 2 daughter cells.
A new nuclear envelope forms around the chromosomes late in telophase.
The chromosomes may disappear late in telophase.