1. Cell Growth and Division
Chapter 10
Cell Growth and Division

2. 10-1 Cell Growth Objectives:
Explain the problems that growth causes for cells
Describe how cell division solves the problems of cell growth

3. Limits to Cell Growth Cells are small for a reason As cells grow
1. Greater demand is placed on the DNA
-DNA is responsible for all cell functions, so a larger cell means more cellular reactions that need to take place
2. Moving materials in and out of the cell becomes more difficult

4. Ratio of Surface Area to Volume
Cell Size
5 cm
10 cm
Surface Area (l×w×6)
150 cm2
600 cm2
Volume (l×w×h)
125 cm3
1000 cm3
SA to Volume Ratio
150/125 = 6:5
600/1000 = 6:10
Volume increases more rapidly than surface area
Becomes difficult for cells to bring in necessary nutrients and eliminate waste produced

5. Division of the Cell Process by which a cell divides in two Reasons:
Growth (multicellular organism)
Repair (multicellular)
Reproduction (unicellular, asexual)
Maintenance
Before cells can divide, DNA must be copied
Each daughter cell receives a complete copy of the cell’s genetic information
Resulting cells are small enough (increased ratio of surface area to volume) to allow for efficient materials exchange with environment

6. 10-2 Cell Division Objectives:
List and explain the main events of the cell cycle
Describe the 4 stages of mitosis

7. Cell Division in Prokaryotes vs. Eukaryotes
Prokaryotes- copy the single chromosome and split contents into two cells
Called binary fission
Eukaryotes, more complex process
Mitosis-division of nucleus, followed by
Cytokinesis- division of cytoplasm

8. Chromosomes
Chromosomes are made of DNA that is highly organized

9. Chromosome Structure You are looking at a chromosome and its copy
The result is identical sister chromatids attached by a centromere
One chromatid goes to each of the daughter cells
A human body cell entering cell division contains 46 chromosomes, each of which contains 2 sister chromatids

10. chromosome How many chromosomes do we have now? (condensed form)
Fight the urge. This is still considered a SINGLE chromosome since they are identical and attached. After replication of the chromosome, it is still considered one chromosome!

11. Diploid Number
Each organism has a specific number of chromosomes, for humans it is 46
23 pairs of homologous chromosomes
The total number is referred to as the diploid number (2n)

12. Chromosome Numbers

13. The Cell Cycle
The Cell Cycle is a series of events that cells go through as they grow and divide
It’s a combination of 2 main phases
Interphase- the period of growth between divisions
Includes 3 subphases G1, S, and G2
(accounts for ~90% of time spent in cell cycle)
M phase- consisting of mitosis and cytokinesis

14. Cell Cycle
Actively dividing cells take about 24 hours to complete this cycle
Cells that don’t divide are “stuck” in G1
Interphase
M phase

15. Interphase Consists of G1 phase (growth, really gap)
S phase (synthesis of DNA)
G2 phase (growth, really gap)

16. G1 Phase Cell grows in size Protein and organelle production increased
Gather and synthesize nutrients
ex. Make the 6 billion nucleotides needed to replicate the DNA. Acquire/synthesize enough amino acids to build all the required proteins to divide the cell, etc…
Cells can hang in this subphase for a very long time like certain muscle cells or forever like cardiac (heart) muscle or neurons, which do not divide at all…

17. S phase Enzymes make an exact copy of the DNA Centrosomes replicate
Every chromosome has a copy, DNA has doubled, but there are still only 46 chromosomes
Why?? Remember that sister chromatids (original DNA and the copy) only equal one chromosome
Centrosomes replicate
Centrosomes, also called asters, hold the centriole pair

18. Centrosome Structure
Microtubules from the centrioles are what pull sister chromatids apart during mitosis

19. G2 phase More growth and organelle production
Shortest of the Interphase subphases
Once finished, mitosis begins
M phase

20. Mitosis Four Stages: Prophase (pro- means first)
Metaphase (meta- means middle/after)
Anaphase (ana- means apart)
Telophase (telo- means far away/end)

21. Prophase Longest phase of mitosis Chromosomes become visible
Centrioles (animal cells only) migrate to opposite ends of the cell
Mitotic spindle starts to form
Spindle fibers form in foot ball shape across cell
Spindle attaches to each chromosome near the centromere
Chromosomes coil more tightly
Nuclear envelope and nucleolus disintegrate

22. Prophase
Chromatin condenses into chromosomes

23. Metaphase Chromosomes line up in the middle (equator) of the cell
Spindle fibers attach to centromeres

24. Metaphase

25. Anaphase
Centromere holding sister chromatids together splits separating chromosomes
Spindle fibers shorten, pulling chromatids apart to opposite ends of cell
Animal cells begin to pinch in
Plant cells begin to form cell plate in the middle

26. Anaphase

27. Telophase
Nuclear membrane built from ER around each set of chromosomes
Nucleolus reforms in each nucleus
Spindle breaks down
Chromosomes become mass of chromatin again

28. Telophase Two cells dividing into four
Cleavage furrow forming (animal cells)

29. Cytokinesis
Final division of cytoplasm resulting in two daughter cells
Animals – cell membrane pinches together
Plants – cell plate forms new cell membrane dividing the daughter cells
Often happens at the same time as telophase

30. 10-3 Regulating the Cell Cycle
Objectives:
Explain how the cell cycle is regulated
Explain how normal cells and cancerous cells are different

31. Regulating the Cell Cycle
The controls on cell growth and division can be turned on and off.
For example, broken bone stimulates cells to divide rapidly and start the healing process.
Rate of cell division slows when the healing process nears completion.

32. Regulating the Cell Cycle
Internal regulators are proteins that respond to events inside a cell.
They allow the cell cycle to proceed only once certain processes have happened inside the cell.
Ex: cyclins
External regulators are proteins that respond to events outside the cell.
They direct cells to speed up or slow down the cell cycle.
Growth factors are external regulators that stimulate the growth and division of cells.
Important during embryonic development and wound healing.

33. Internal Regulation
Cyclins- family of proteins that regulate the cell cycle in eukaryotic cells
Discovered in the 1980s
When injected into a nondividing cell, a mitotic spindle will form

34. Internal Regulation
This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs.

35. External Regulation Apoptosis is a process of programmed cell death.
Can be caused by growth factor deprivation
Plays a role in development by shaping the structure of tissues and organs in plants and animals.
Ex: Foot of a mouse is shaped the way it is partly because the toes undergo apoptosis during tissue development.

36. Uncontrolled Cell Growth
Cancer occurs when cells lose the ability to control division
Don’t respond to regulatory signals and form tumors as a result
Tumors are masses of cells
Benign tumors do not spread to healthy tissue or other parts of the body
Malignant tumors spread to other parts of the body (i.e. cancer)
The spread of cancer cells is called metastasis. Cancer cells absorb nutrients needed by other cells, block nerve connections, and prevent organs from functioning

37. Cancer
Cells placed in a petri dish filled with a nutrient broth will cover the surface in a thin layer
They stop growing when they come in contact with each other
Molecules on neighboring cells can have an inhibiting effect on cell division

38. - Initially a couple of cells are put into the flask coated with collagen or some other extracellular matrix material
- The cells will start dividing immediately until they cover the entire plate and then they STOP.

39. - Initially a couple of cells are put into the flask
- The cells will start dividing immediately until they cover the entire plate and then they STOP.
What do you think would happen if you were to scrape away some of the cells?

40. - Initially a couple of cells are put into the flask
- The cells will start dividing immediately until they cover the entire plate and then they STOP.
What do you think would happen if you were to scrape away some of the cells?
Cell division turns on in the cells next to the cells that were removed and they fill in the empty space.

41. Cancer Commonality is control over cell cycle has broken down
Often a defect in p53 gene
p53s job is to halt cell cycle until all chromosomes have all successfully replicated
When defected causes cells to lose the information needed to respond to growth signals.
Chromosomal damage results in cells that have lost vital information that regulates cell division

42. Cancer Causes and Treatment
Causes include:
tobacco use
radiation exposure
viral infection
Treatment:
Some localized tumors can be removed by surgery.
Many tumors can be treated with targeted radiation.
Chemotherapy is the use of compounds that kill or slow the growth of cancer cells.