Transcript Stage 2 - Mitosis

The Cell Cycle
Most cells undergo a regular
sequence of growth and division
known as the cell cycle.
The Cell Cycle consists of three stages.
Stage 1:
Interphase - The stage where a cell grows
and the DNA is duplicated in order to get
ready for cell division.
Stage 2:
Mitosis - The stage where a cell seperates
its DNA into two identical sets. Mitosis
occurs in 4 steps.
Stage 3:
Cytokinesis - The stage where a cell
divides into two new daughter cells that
are identical to the parent.
Stage 1 - Interphase
Most of a cells life (90%) is spent in interphase. During this
time, the cell grows & functions normally and prepares for cell
division by copying its DNA in a process called replication.
In this photograph, a cell from a fish is
shown. The circle in the center of the cell
is the nucleus. The black stringy material
in the nucleus is the DNA. This DNA is
copied during Interphase, and when this is
finished the cell has two complete sets of
DNA.
Inter is a prefix that means “between.”
Stage 2 - Mitosis
Mitosis is the process of asexual cell division used by most
cells. (Cells incvolved in sexual reproduction use the other method,
called meiosis.) Mitosis occurs in 4 steps.
Prophase
Metaphase
Anaphase
Telophase
During these 4 steps, the DNA that was duplicated during
Interphase seperates to form 2 new nuclei that each have a
single set of complete DNA.
Stage 2A: Prophase
Prophase is the first step of mitosis. In this step, the DNA
gathers together and forms chromosomes in order to get ready to
divide.
Tiny “threads” of DNA coil up to form
chromatids that join to form chromosomes.
The nuclear membrane dissolves, and two
points (called centrioles) form at the
opposite ends of the cell.
Later the daughter cells will form around
these centrioles.
Pro is a prefix that means “before or primary” (first).
Chromosomes
Each chromosome is made of two identical strands of coiled DNA
(called chromatids) that are joined in the center by a centromere.
These two strands later separate to make an identical copy for each
of the two daughter cells.
Strand 1
Strand 2
Strand 1
Strand 2
Stage 2B: Metaphase
Metaphase is the second stage in mitosis. During this step, the
chromosomes line up in the center of the cell (between the
centrioles at each end), and get ready to divide. Spindle fibers
attach each chromosome to the centrioles like small strings.
In this photograph, the chromosomes
have lined up in the center of the cell.
The centrioles are visible at each end and
spindle fibers attach the chromosomes to
them.
Meta is a prefix that means “after or behind.”
Stage 2C: Anaphase
Anaphase is the third stage of mitosis. In this step, the
chromosomes separate and then begin to pull apart and move to
opposite ends of the cell.
In this photograph, the chromosomes
have separated and are being pulled to
the opposite ends of the cell by spindle
fibers attached to each centriole.
Ana is a prefix that means “upward, back, or again.”
Stage 2D: Telophase
Telophase is the fourth stage of mitosis. In this step, the two
sets of chromosomes form two new nuclei, and the cell divides.
In this photograph, the chromosmes have
separated into two distinct groups. A new
nuclear membrane forms around each,
creating two nuclei - one for each daughter
cell.
Telo is a prefix that means “end.”
Stage 3: Cytokinesis
Cytokinesis is the last stage of the cell cycle. In this step, the
cell membrane “pinches in” between the two new nuclei, and forms
two separate daughter cells. During this phase the cytoplasm and
organelles of the cell are divided between the two daughter cells.
In this picture, the cell has divided in half
and Mitosis is complete. Each daughter
cell has its own set of DNA which is
identical to the original cell.