1. Be able to: Explain the problems that growth causes for cells.
Describe how cell division solves the problems of cell growth.
Name and describe the main events of the cell cycle.

2. Let’s do some math! Calculate the surface area of each sphere.
      
           
Let’s do some math!
Calculate the surface area of each sphere.
Calculate the volume of each sphere.
Then, calculate the surface area to volume ratio. Round #’s up or down to make it easier.
S.A. = 4 (pi) r 2
Radius 2cm
S.A. = ________
V = __________
Ratio SA:V = ________
Radius 2cm
S.A. = ___50cm2__
V = __33cm3____
Ratio SA:V = 50:33_or 1.51:1

3. S.A. = 4 (pi) r 2 Radius 1cm S.A. = _____ V = ______ Ratio SA:V = ___
S.A. = __13cm2___
V = __4cm3____
Ratio SA:V = _13:4 or 3.25:1__
Radius 2cm
S.A. = ___50cm2__
V = __33cm3____
Ratio SA:V = 50:33_or 1.51:1
Radius 3cm
S.A. = __113cm2_
V = ___113cm3___
Ratio SA:V = _113:113 or 1:1__
Radius 3cm
S.A. = _____
V = ______
Ratio SA:V = ___
S.A. = 4 (pi) r 2
As the spheres get larger what happens to the SA:V ratio?

4. 1st problem: Cell size and material exchange
The larger a cell grows the more trouble it has…
moving enough nutrients in
Moving all the waste materials out

5. 2nd problem: DNA overload A larger cell makes greater demands on its genetic library.

6. Checkpoint! What are two problems that cell growth causes for cells?
The larger a cell becomes, the more demands the cell places on its _____ and the more trouble the cell has moving enough _________and _________ across the cell membrane.
What is viable solution for cells solve these problems?
Cell Division – A larger cell splits into two smaller daughter cells.

7. The Cell Cycle - series of events that cells go through as they grow and divide
The cell cycle is divided into two halves
Interphase - period of the cell cycle between cell divisions
M phase – period of time when mitosis and cell division occurs

8. Parts of Interphase G1 Phase Growing
Synthesize new proteins and organelles
Doing their jobs
Longest phase of cell cycle
S Phase
Chromosomes(DNA) are replicated
Key proteins associated with replication are made (centromeres)
G2 Phase
Shortest of the 3 phases of interphase
Organelles and molecules for cell division are produced (centrioles)
Check-up phase before mitosis

9. Chromatin and Chromosomes
Chromatin - A complex of DNA and proteins in the cell nucleus that condenses to form chromosomes during cell division.
Chromosomes – Condensed Chromatin
They are the same stuff, just in different forms

10. Chromatin condenses in chomosomes before mitosis begins
Chromosomes

11. Chromosomes Different organisms have different #’s of chromosomes
Humans cells – 46
Fruit Fly cells – 8
Carrot cells – 18
King Crab cells - 208
Note: Chromosomes are not visible in most cells except
during cell division.

12. Chromosomes Replication
During the cell cycle (before cell division can take place) chromosomes are replicated to form an identical copy of itself.
Two identical copies of a chromosome are called “sister” chromatids – (one of two identical “sister” parts of a duplicated chromosome)
Centromere - area where each pair of the chromatids of a chromosome are attached

13. M Phase, Cell Division and Mitosis

14. Mitosis (PMAT) Prophase 1. Chromosomes become visible
2. Centrioles take up positions on opposite sides of the nucleus
Metaphase
1. Chromosomes line up across center of cell (Metaphase-Middle)
Anaphase
1. The chromosomes move until they form two groups near the poles of the spindle (guides that help separate the chromosomes)
Telophase
1. A nuclear envelope re-forms around each cluster of chromosomes
2. The nucleolus becomes visible in each daughter nucleus

20. Cytokinesis Cytoplasmic division and other changes exclusive of nuclear division that are a part of mitosis or meiosis
In animal cells the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts
In plant cells a cell plate forms midway between the divided nucleus

21. In plant cells, a cell plate forms
In plant cells, a cell plate forms. The cell plate is synthesized by the fusion of multiple membrane-bounded vesicles. Their fusion supplies new plasma membrane for each of the two daughter cells. Synthesis of a new cell wall between the daughter cells then occurs at the cell plate.

22. Controls on Cell Division

23. Answer
The cells would form more layers but would probably begin to die off when space and nutrients ran short and wastes accumulated.

24. How do cells know when to divide and when not to?
Internal regulators – proteins that respond to events inside the cell.
Some proteins make sure cells do not enter mitosis until all of the chromosomes have been replicated.
What stage of the cell cycle do you think these proteins work?
G2 phase
Cyclins – (internal regulator) one of a family of closely related proteins that regulate the cell cycle in eukaryotic cells

25. Cyclins

26. External Regulators
External regulators - Proteins that respond to events outside the cell are called external regulators.
External regulators direct cells to speed up or slow down the cell cycle.
Growth factors are among the most important external regulators, which tell cells to speed up division. When is this important?
(Answer: During embryonic development and wound healing)
Molecules found on the surfaces of neighboring cells often have an opposite effect, causing cells to slow down or stop their cell cycles.

27. Uncontrolled Cell Growth
Cancer cell
Various forms of cancer have many causes
Smoking
Radiation
Viral infections
The common thread in all cancers is that control over the cell cycle has broken down.
Many cancer cells have a defect in the p53 gene which makes a protein that stops the cell cycle if the chromosomes have not been replicated properly

28. Checkpoint!
1. The break down of a cell’s entire life is the _______ ________.
2. The phase of the cell cycle when the cell is growing, replicating DNA and getting ready for mitosis is _____________.
3-6. What are the four phases of Mitosis?
7. The process of a cell actually splitting in two is called _______________.