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Transcript of Cell Division
All organisms grow and reproduce.
Fawn - growth, development
Bacteria - divide to reproduce
Cell division is a simple process in prokaryotes
Cell division is more complex
Cell Division in Prokaryotes
Prokaryotic cell division
in which the cell divides into two halves.
All eukaryotic cells store genetic information in the nucleus in a structure known as a
- Human cells have
It takes about 40 min. to make one complete copy of the E. coli genome. E. coli can divide (under ideal conditions) in as little as 20 minutes. How is this possible?
It turns out that E. coli can begin a new round of DNA replication before the previous round is complete. When the cell splits in two, each daughter cell receives a strand of DNA that is already in the process of being copied. That is, the daughter cell receives DNA that is halfway prepared for the eventual granddaughter cells.
Importance of Chromosomes
Chromosomes are composed of a relaxed form of DNA and protein called
This is found in the nucleus
DNA coils, so it can fit!
Structure of Chromosomes
Think about this
What are homologous chromosomes
Living organisms need cell division for 3 reasons:
Above: Kevin Ware's horrific broken leg.
Below: Ware's leg during recovery. Without cell division repairing his injury, he would not be able to play b-ball again.
Photos: Muhammad Ali, Michael J. Fox, and Christopher Reeves
What type of cells are being affected in their conditions/injuries?
Why can't their bodies repair like Kevin Ware's body?
Why are these men &/or their families such strong advocates for stem cell research?
The Cell Cycle
will move to opposite ends of the cell and form
help pull chromosomes apart during mitosis.
Spindle apparatus=fibers and centrioles
nucleus divides and nuclear material divide
- spindle apparatus forms with the help of
, nuclear membrane breaks apart. Chromatid condenses into chromosomes.
- chromosomes align at cell's
- sister chromatids pull apart (centromeres divide) toward
of the cell
- spindle disappears, chromosomes are at opposite poles,
nuclear membrane reforms
around each set of sister chromatids. Chromosome decondense
(happens after telophase)
4 Cell cycle checkpoints
= proteins that check to see if the cell is ready to move to the next stage. G1, S, G2, M
What happens in the cell cycle of a cancerous cell?
can't regulate because of mutations
Cell growth continues
forms, crowding out normal cells
Average Cell Division Times
Cell Type Process Time
fly embryo mitosis 8 minutes
bacteria mitosis 20 minutes
yeast mitosis 2 hours
human skin mitosis 20 - 24 hours
human sperm meiosis about 64 days
human liver mitosis 1 year or more
human egg meiosis up to 40 years or more
human nerve mitosis never, once mature
Comparison of average cell division times
What causes cancer?
There are many reasons that cells can divide and grow out of control, including
genetic causes, nutritional deficiencies, some infections, or exposure to environmental causes, such as
(ex: pollution & tobacco)
ultraviolet (UV) radiation from the sun
Remember the Centrioles??
A stem cell is an unspecialized cell that can have the potential to develop into specialized cells under certain conditions.
Stem Cell Types
Adult Stem Cells-->Come from various tisssues in the body; present from infancy through adulthood.
Embryonic-->100-150 Cells formed after fertilization; will become specialized as the embryo grow.
center of chromosome where sister chromatids attach
structure in a chromosome containing identical copies of DNA
The stage of the cell cycle during which the
carries out normal functions (metabolism)
copies its DNA (chromosomes)
prepares for division
(LONGEST phase of cell's life)
Regulating Cell Cycle
-process of programmed cell death
--> Protein that binds to cyclin-dependent kinases to regulate the activities of the cell cycle
--> enzymes that are activated by cyclins and serve to regulate the activities of the cell cycle
to control the cell cycle. Different combination of
start the cell cycle at different checkpoints and monitor throughout. In the
the cell is growing and replicating. DNA replication happens during
takes inventory before moving into
. The cycle ends with
Cells must be small to diffuse nutrients quickly
cell gets too large
nutrients and wastes
they become too large
As a cell grows larger, its
increases more rapidly than its
, then the surface area to volume ratio
are carriers of genetic mateiral
exist as chromatin in the nucleus
appear during prophase
must replicate accurately to insure cell survival