1. Cell Growth and Division
Chapter 10
Unit 3

2. A. Cell Growth
There are limits to cell growth, cell size is limited for 2 reasons
The larger a cell is, the more demand is made upon its DNA. As a cell grows it does not make extra DNA
The more trouble it has getting nutrients and wastes across the cell membrane
Cells receive and discard material through their membrane, the rate at which this happens is based on the cells surface area.

3. B. Volume to Surface Area
The ratio of volume to surface area is extremely important for a cell, to be able to get nutrients quickly enough to sustain life processes.

4. C. Chromosomes
In eukaryotic cells the genetic information is contained in DNA which is carried in chromosomes.
Chromosomes are copied before each cell begins its division, and then attached to its identical copy, this is called a chromatid.
Where the chromatids attach is called the centromere, and it is usually located near the center of the chromatid.
Each organism has its own number of chromosomes.
Humans have 46
Fruit flies have 8
Horses have 64
The number of chromosomes does
not determine the complexity of the
organism.

5. Time required for Cell Division

6. Cell Rap – will watch after notes…
D. Cell Division
Cell Rap – will watch after notes…

7. 1. Interphase – 1st stage
During interphase the cell grows, makes a copy of its DNA and prepares to divide into two cells.
During the first part of interphase the cell grows to its full size and produces structures it needs. For example the cell makes new ribosomes and produces enzymes. Copies are made of both mitochondria and chloroplasts.
Each daughter cell must have a complete set of DNA in order to survive.
At the end of DNA replication each cell contains two identical sets of DNA.
Once the DNA has replicated preparation for cell division begins (Mitosis)

8. 2. Mitosis
Mitosis is the second stage of the cell cycle. This is the stage when the cells nucleus divides into two nuclei.
During mitosis, one copy of the DNA is distributed into each of the two daughter cells.
Mitosis is divided into four phases: prophase, metaphase, anaphase and telophase.

9. 3. Prophase
During prophase the thread like chromatin in the nucleus condenses to form double-rod structures called chromosomes.
Each chromosome has two rods because the cell’s DNA has replicated, and each rod in a chromosome is an exact copy of the other.
Each rod in a chromosome is called a chromatid the chromatids are held together by a structure called a centromere.
Spindle fibers form to form a bridge between the ends of the cell; and the nuclear envelope breaks down.

10. 4. Metaphase - middle
During metaphase the chromosomes line up across the center of the cell. Along the equator
Each chromosome attaches to a spindle fiber at its centromere.

11. 5. Anaphase - apart During anaphase the centromeres split.
The two chromatids separate, and each chromatid becomes a new chromosome.
The new chromosomes move to opposite ends of the cell. The cell stretches out as the opposite ends are pushed apart.

12. 6. Telophase
During telophase the chromosomes begin to stretch out and lose their rod like appearance.
A new nuclear envelope forms around each group of chromosomes.
MITOSIS ENDS!

13. 7. Cytokinesis – Final Stage
During cytokinesis the cell membrane pinches in around the middle of the cell.
The cell splits in two.
Each daughter cell ends up with the same number of chromosomes as the parent cell.
The cell cycle takes on average 22 hours from start to finish, however mitosis is only a small part of the cycle.

14. Cell Division of a Liver Cell

15. Human development 1st week

16. LOL

17. E. Regulating the Cell Cycle
When cells are grown in a lab, if they fill a petri dish so that they are touching, they stop growing and dividing.
This tells us that cell division and growth can be turned on and off as needed.
In the 1980’s Tim Hunt & Mike Kirschner (and others) found a protein that induced cell division through experimentation.
This protein was named cyclin because it regulated the cell cycle. When this protein appears in abundance, the cell knows it’s time to divide!
Since this time a whole family of cyclins has been discovered.

18. F. Uncontrolled Cell Growth
Cancer is the consequence of uncontrolled cell growth in a multicellular organism
Cancer cells do not respond to the signals that regulate the growth of most cells. As a result they form masses of cells called tumors that can damage surrounding tissues.
Cancer cells no longer have growth regulators.
Many cancer cells have a break down in a gene called P53 which halts the cell cycle until all chromosomes have been properly regulated.
This causes chromosomal damage to build up creating cells that do not respond to cell regulation.

19. G. Stem Cells
The cells that form during the first few divisions after fertilization can become any type of cell.
During development (in utero) most cells become differentiated
Meaning that they become a specific type of cell
Once a cell is differentiated it cannot become another type of cell.
Stem cells can be used to repair damaged cells in adults, however this is an ethical issue when discussing human embryonic stem cells.