Transcript File

What is Mitosis?
Mitosis is when the cell’s nucleus divides into two new nuclei
and one copy of the DNA is distributed into each daughter
cell.
New cells formed are called daughter cells.
Why Do Cells Need to Divide?
Cells want to divide for several reasons:
1) Large cells can’t control their functions as well as small
cells-- as a cell gets bigger, it still the same amount of DNA
to do the same jobs
2) Large cells can’t exchange materials as well-- the ratio of
surface area (cell membrane) to cell volume decreases as a
cell gets bigger, making it harder for food to get in and
wastes to go out
3) As cells age, they aren’t as efficient
The Cell Cycle
Cells aren’t constantly dividing; instead, cells grow, live their
lives and then divide when necessary. Cell cycle -- this
process of growth and division is known as the
The cell cycle consists of three parts:
Interphase
-- interphase is further divided into three parts
Mitosis
-- mitosis is also divided into four parts called
prophase, metaphase, anaphase, and
telophase
Cytokinesis
-- Completes the process of cell division
Image of the Cell Cycle
Interphase
The cell cycle begins when a new daughter cell is formed
and immediately begins interphase. During interphase, the
cell undergoes the following life “phases”
1. Cells grow to their mature size
2. Cells replicate their DNA so that they have a copy for
each new daughter cell.
3. Cells also manufacture new proteins and organelles
preparing to divide into two cells.
ONCE THIS HAPPENS MITOSIS IS READY TO BEGIN!!
About Chromosomes
Chromosomes are only visible when mitosis is about to
begin and during mitosis.
Chromosomes consist of a chromatid (a strand of DNA) with
a condensed area called the centromere. Centromeres are
near the middle of a chromatid.
DNA (and therefore chromosomes) are replicated during the
interphase, so each chromosome actually consists of two
“sister” chromatids.
Humans have 23 matching pairs of chromosomes, for a
grand total of 46 chromosomes
Image of a Chromosome
Mitosis
Biologists usually consider the first four parts to be actual
“mitosis”,
The parts of mitosis are:
-- prophase
-- metaphase
-- anaphase
-- telophase
The final part of the cell cycle, cytokinesis, happens later.
Prophase
Prophase is the longest
phase of mitosis
During prophase:
-- the centrioles line up on
opposite sides of the
nucleus
1. Chromatin condenses into visible chromosomes
2. Structures called spindle fibers form a bridge between
each end of the cell.
3. Nucleolus disappears and nuclear membrane breaks
down
Metaphase
Metaphase only last for a few minutes
During metaphase:
1. Chromosomes line up across the center of the cell
2. Chromosome attach to the spindle fibers at the
centromere
Anaphase
During anaphase:
1. Centromeres that join sister chromatids separate and the
chromatids become individual chromosomes
2. Chromosomes move apart until they reach the centrioles
near the end of the spindle
3. Cell becomes stretched out as the opposite ends pull
apart.
Anaphase ends
when the
centrioles stop
moving
Telophase
During telophase:
1. Chromosomes begin to
tangle back into chromatin and
lose their rod-like appearance
2. Nuclear membrane begins
to re-form around each set of
chromosomes
3. Spindle fibers break
4. Nuceloli become visible in
each new nucleus
END OF MITOSIS
Cytokinesis
Although cells have split up their genetic material and formed
new nuclei, the cells are not split.
Cytokinesis is the process by which cells split their
cytoplasm into two new daughter cells
In animals, cytokinesis happens when the cell membrane is
drawn in and the cell divides into two new cells
In plants, a structure made of wall-building vesicles, called a
cell plate forms between the two new nuclei, and eventually
becomes a dividing membrane
Full Diagram of Mitosis