1. Warm-up 11/11/14
Why is there a limit to cell size? Why do we not have cells as big as buildings?

2. Which turtle has bigger cells?
Neither!!!
Their cells are the same size… this one just has MORE!

3. Why don’t cells continue to grow?
There are two main reason why cells divide instead of continue to grow:
The larger the cell becomes, the more demands the cell places on its DNA
The cell has more trouble moving enough nutrients and wastes across the cell membrane.

4. DNA “Overload”
Information that controls a cell’s function is stored in a molecule knows as DNA
In eukaryotic cells, DNA is found in the nucleus

5. DNA “Overload”
When a cell is small, the information stored in the DNA is able to meet all of the cell’s needs
If a cell was too large an “information crisis” would occur and the cell would not function properly

6. Example: Small library in a large city

7. Exchanging Materials
Food, water and nutrients enter the cell through its cell membrane
Waste products leave in the same way

8. Exchanging Materials
Example: Small streets in a big town

9. Exchanging Materials
The relationship between a cell’s volume and its surface area is the key to understanding why cells must divide as they grow!

10. Ratio of Surface Area to Volume

11. Ratio of Surface Area to Volume
The volume increases much faster than the surface area, causing the ratio of surface area to volume to decrease.
This decrease creates serious problems for the cell.
Formula for calculating ratio:
Ratio = Surface Area/Volume

12. Cell Division
Photo Credit: © CAMR/A.B. Dowsett/Science Photo Library/Photo Researchers, Inc.

13. Cell Division
In eukaryotes, cell division occurs in two major stages. The first stage, division of the cell nucleus, is called mitosis. The second stage, division of the cell cytoplasm, is called cytokinesis.

14. Cell Division
DNA to Chromatin to Chromosomes

15. Chromosomes
Genetic information is passed from one generation to the next on chromosomes.
Before cell division, each chromosome is duplicated, or copied.

16. Chromosomes
DNA

17. Chromosomes
Each chromosome consists of two identical “sister” chromatids. Each pair of chromatids is attached at an area called the centromere.
Sister chromatids
Photo Credit: © Gunther F. Bahr/AFIP/Stone
Centromere
Copyright Pearson Prentice Hall

18. When the cell divides, the chromatids separate
When the cell divides, the chromatids separate. Each new cell gets one chromatid.

19. The Cell Cycle
The cell cycle is the series of events that cells go through as they grow and divide. Interphase is the period of growth that occurs between cell divisions.

20. During the cell cycle: a cell grows prepares for division
divides to form two daughter cells, each of which begins the cycle again

21. The cell cycle consists of four phases:
G1 (First Gap Phase)
S Phase
G2 (Second Gap Phase)
M Phase
G0 Phase (Resting
phase)

22. Events of the Cell Cycle
During G1, the cell
increases in size
synthesizes new proteins and organelles

23. During the S phase,
chromosomes are replicated
DNA synthesis takes place
Once a cell enters the S phase, it usually completes the rest of the cell cycle.

24. The G2 Phase (Second Gap Phase)
organelles and molecules required for cell division are produced
Once G2 is complete, the cell is ready to start the M phase—Mitosis

25. Cell Cycle
During the cell cycle, the cell grows, replicates its DNA, and divides into two daughter cells. DNA synthesis takes place during the S phase. Cell division takes place during the M phase. G1 and G2 are gap phases.

26. Mitosis
Biologists divide the events of mitosis into four phases: (PMAT)
Prophase
Metaphase
Anaphase
Telophase

27. Mitosis
Most eukaryotic cells go through a regular cycle of interphase, mitosis and cytokinesis. Mitosis has four phases: Prophase, Metaphase, Anaphase and Telophase. The events shown here are typical of animal cells.
Mitosis

28. Chromosomes (paired chromatids)
Section 10-2
Spindle forming
Prophase
Mitosis
Prophase
Chromosomes (paired chromatids)
Centromere
Most eukaryotic cells go through a regular cycle of interphase, mitosis and cytokinesis. Mitosis has four phases: Prophase, Metaphase, Anaphase and Telophase. The events shown here are typical of animal cells.

29. Prophase Prophase is the first and longest phase of mitosis.
The centrioles separate and take up positions on opposite sides of the nucleus.
Spindle
forming
Centromere
Chromosomes
(paired chromatids)

30. Spindle
forming
The spindle is forming and the pairs chromosomes are visible. The centrosome helps to organize the spindle, a fanlike microtubule structure that helps separate the chromosomes.
Centromere
Chromosomes
(paired chromatids)

31. Spindle
forming
Chromatin condenses into chromosomes. The centrioles separate and a spindle begins to form. The nuclear envelope breaks down.
Centromere
Chromosomes
(paired chromatids)

32. Mitosis
Metaphase
Centriole
Spindle
Centriole
Metaphase

33. Metaphase The second phase of mitosis is metaphase.
The chromosomes line up across the center of the cell.
Microtubules connect the centromere of each chromosome to the poles of the spindle.
Centriole
Spindle

34. Individual chromosomes
Anaphase
Individual chromosomes
Anaphase

35. Anaphase Anaphase is the third phase of mitosis.
Individual
chromosomes
Anaphase
Anaphase is the third phase of mitosis.
The sister chromatids separate into individual chromosomes.
The chromosomes continue to move until they have separated into two groups.

36. Nuclear envelope reforming
Telophase
Nuclear envelope reforming
Telophase

37. Telophase Telophase is the fourth and final phase of mitosis.
Chromosomes gather at opposite ends of the cell and lose their distinct shape.

38. A new nuclear envelope forms around each cluster of chromosomes.

39. Cytokinesis
Cytokinesis

40. During cytokinesis, the cytoplasm pinches in half
During cytokinesis, the cytoplasm pinches in half. Each daughter cell has an identical set of duplicate chromosomes

41. Cytokinesis in Plants
In plants, a structure known as the cell plate forms midway between the divided nuclei.
Cell plate
Cell wall

42. The G0 Phase (resting phase)
The cell leaves the cell cycle and quits dividing.
This may be a temporary resting period or more permanent.
Ex: Nerve cells and heart muscle cells no longer divide after reaching maturity.