Cell division in human ( M - phase and interphase)

Cell division , M phase and interphase

1. Cell division
How one cell becomes two

2. Mitosis + Cytokinesis = Cell division
•Most cells in all eukaryotic organisms will divide
many times throughout the life of the organism
–Mitosis is the process by which a cell duplicates its
genetic materials (chromosomes and prepares for
cell division
–Cytokinesis is the division of the rest of the cell into
two different daughter cells
–Prokaryotes also divide through binary fission, but this
is NOT mitosis/cytokinesis
•In animals, cell division occurs during embryonic
development, growth, and wound healing
•Errors during cell division can cause cell death
or cancer

3. Mitosis reorganizes DNA in the cell
•Prior to mitosis, the cell creates an exact
duplicate of its DNA material
•During mitosis, the two copies are reorganized,
repackaged into two sets of chromosomes, and
divided to opposite ends of the cell
•In most organisms, mitosis is immediately
followed by cytokinesis (the cell body dividing in
two)
•The original cell (mother cell) is identical to the
two resulting cells (daughter cells)

4. Mitosis vocabulary
•Nucleus –location of DNA inside the cell
•Nuclear envelope –the membrane that separates the nucleus from the cytoplasm
•DNA –an incredibly long molecule that contains genetic blue prints for cell behavior
•Chromatin –a loosely bundled coil of DNA. Most of the time, DNA is organized in
this form, “ a loose rope”
•Histones –proteins which hold a DNA strand together in the form of chromatin
•Chromosome –a highly organized form of chromatin, “a tightly wrapped and carefully
knotted rope ”
–Each chromosome is composed of two identical parts called chromatids
–Chromatids: two halves of a chromosome which contain the same genetic information
–DNA exists in the form of chromosomes only during mitosis
–Each chromosome looks like an X
•Centromere –a bundle of proteins which connects the two chromatids of a
chromosome, the “knot at the center of the X“
•Microtubules –part of a cell’s cytoskeleton. These are tubes of protein which use to
pull chromosomes apart and to opposite ends of a cell during mitosis. They are
powered by ATP!
•Mitotic spindle –How microtubules are organized during mitosis. This is a collection
of microtubule fibers which is formed to coordinate the pulling of apart of
chromosomes.
•Metaphase plate –the line along which chromosomes are lined up during mitosis.
This arrangement is coordinated by the mitotic spindle.

5. Chromosome Structure

6. 5 Phases of Mitosis
•Mitosis is composed of five phases
–Prophase
–Prometaphase
–Metaphase
–Anaphase
–Telophase
•During each phase, different proteins in the cell
perform specific roles to divide the two copies of
genetic material
•Cytokinesis occurs after mitosis to create two cells

8. Prophase
•Chromatin is being organized
into chromosomes inside the
nucleus
•Microtubules are organized
into mitotic spindles in the
cytoplasm
•Nuclear envelope is dissolving
•By the end of prophase
–Chromosomes and mitotic
spindle are fully organized
–Nuclear envelope has
disappeared

9. Prometaphase
•Chromosomes move towards
each other and into the
center of the cell
•Microtubules move into the
nuclear region and begin to
connect to chromosomes at
the centromere
•Microtubules organize into
two mitotic spindles, one at
each end of the cell

10. Metaphase
•The mitotic spindle is
fully organized, and
has pulling the
chromosomes to the
center of the cell
•The spindle aligns
chromosomes so that
each centromere is
lined up along the
metaphase plate (the
center of the cell)

11. Anaphase
•Each chromosome is
pulled apart into two
chromatids (halves) at the
centromere
•Microtubule fibers contract
(using ATP!), pulling
chromatids to opposite
ends of the cell towards
the two spindles

12. Telophase
•Chromatids arrive at opposite
ends of the cell and begin to
unfold into loose coils of
chromatin
•New nuclear envelopes begin
to form around the chromatin to
create two nuclei
•Spindle fibers disperse into the
cytoplasm
•The cell membrane begins to
cleave in preparation for
cytokinesis

13. Cytokinesis
•The cell membrane is being pinched off to
form two separate compartments
•Cytoplasm and organelles are being
divided between the two forming cells
•At the end of cytokinesis, the membrane
fuses to create two daughter cells which
contain identical copies of DNA, and equal
amounts of cytoplasm and organelles
•Cell division is complete!

14. Cell division movies
•http://www.youtube.com/watch?v=VlN7K1-
9QB0
•http://www.youtube.com/watch?v=CzPGh
YiGyZ8&feature=related
•Embryonic division in the worm c.elegans:
http://www.youtube.com/watch?v=zsgOl04
PESI&NR=1
•http://www.cellsalive.com/mitosis.htm