Transcript The Cell Cycle

THE CELL CYCLE
I-PMAT-C
SNC 2DI
Why is cell division important?
1) Healing
and tissue repair

Healing cuts, broken bones, replacing dead cells

Cell division allows an organism to grow bigger
(from one cell to two cells to many cells eventually!)
2) Growth
3) Reproduction

of organisms
Unicellular organisms like bacteria reproduce by
dividing in two. Sexual reproduction in multicellular
organisms occurs when sperm and egg cells are
made from the division of cells in reproductive
organs
If a Cell becomes too large:
◦ Nutrients from outside the cell can’t get to all parts
of the cell quickly
◦ Messages from the nucleus take too long to travel
to all cell parts
◦ Larger cells have less surface area (SA) than
multiple cells of equal volume. Therefore, the larger
cells cannot obtain enough nutrients from the
surrounding environment
FACTORS THAT AFFECT CELL DIVISION

Environment: sunlight, altitude

Antibiotics: inhibit cell growth and mitosis

DNA mutations – can disrupt apoptosis (the
natural death of cells). This happens in
Cancerous cells as an example.
Mitosis
Mitosis (M) and
Cytokinesis
Growth and
Preparation
for Cell
Division (G2)
Rapid Cell
Growth (G1)
DNA
Synthesis (S)
Interphase
Every hour, about one billion (109) cells die and are
replaced in your body.
Cells do not constantly divide. They go through
periods of growth and preparing for cell division.
This sequence of events is called the cell cycle.
When cells are not dividing, they are in a stage
(that has three sections) called interphase.
During the first section this phase, cells go through
a period of rapid growth, where they take in
nutrients (like sugars) and produce new proteins
and organelles.
The cell spends 90% of its time in interphase.
Once the cell has grown to a size where its surface
area is too small to service the large volume, the cell
is unable to absorb enough substances or expel
enough waste.
At this point it is healthier for the cell to divide into two
identical daughter cells.
In preparation for the MITOSIS (M-phase), the cell
prepares for division by doubling its chromosomes
creating two identical copies of DNA called sister
chromatids.
Chromosomes must be duplicated because they
contain very important information about how a cell
functions, and each new cell will need a copy of this
information.
The nucleus divides in a process called mitosis and the
cytoplasm and the rest of the cell divide through a
process called cytokinesis.
The cell grows and carries out its normal functions. It then prepares for cell
division by duplicating its DNA.
-cell is in a resting phase
-technically not part of mitosis, but it is included in the cell cycle
-performing cell functions
-DNA replicates (copies)
-organelles double in number, to prepare for division

When a cell is "resting" i.e. not dividing, the
chromosomes are organized into an
entangled structure called chromatin
In
prophase, the chromatin
condenses into discrete,
double chromosomes.
The nuclear envelope
breaks down
 spindles form at opposite
"poles" of the cell (IN ANIMAL
CELLS) from the centrioles
The double-stranded
chromosomes line up in
the middle of the cell
Each chromosome splits.
The two strands move away
from each other to opposite
poles of the cell
The chromosomes reach
the opposite poles of the
cell and a nuclear
membrane begins to form
around each set
Cytoplasm and its
contents are split into two
equal parts. Cell
membrane pinches to form
two daughter cells.

In this last stage, two distinct daughter cells are
formed after the chomatids have migrated to the
opposite poles. Cytokinesis is also occurring at
this time.





Cyto =cell
Kinesis=movement
The cell’s cytoplasm divides at the end of
telophase
Animals - cell pinches inward
Plants - a new cell wall forms between the
new cells
Mitosis results in two new
cells that are identical to
each other and to the
parent cell. New cells
enter G1/interphase.