Cell Size and Membrane Transport

1. Georgia Performance Standards: • Explain the role of cell organelles for both prokaryotic and eukaryotic cells, including the cell membrane, in maintaining homeostasis and cell reproduction. Cell Size and Membrane Transport Essential Questions: EQ: Why do cells divide? EQ: What limits the size of a Cell? EQ: Why are cells small? EQ: How does cell division help maintain homeostasis for the cell? EQ: Why is mitosis necessary in cell reproduction? EQ: What happens when mitosis goes wrong?

2. Cell Growth • When a living thing grows, what happens to its cells? • Does an animal get larger because each cell increases in size or because it produces more of them? • In most cases, living things grow by producing more cells (Cell Division)

3. Cell Growth & Division • Why do cells divide instead of growing bigger and bigger? (Two main reasons) • When cells become large: 1. The cell places more demands on its DNA 2. It’s more difficult for cells to move enough nutrients and wastes across the cell membrane

4. Ratio of Surface Area to Volume  • Imagine a cell that is shaped like a cube with each side having a length of 1 cm • The surface area = length × width × number of sides 1 cm × 1 cm × 6 = 6 cm2). • The volume of the cell = length × width × height 1 cm × 1 cm × 1 cm = 1 cm3 • To obtain the ratio of surface area to volume, divide the surface area by the volume. • The ratio of surface area to volume would be 6 / 1, or 6 : 1.

6. If the length of the cell doubled, what would happen to the cell’s surface area compared to its volume? The cell’s surface area = 2 cm × 2 cm × 6 = 24 cm2 The volume = 2 cm × 2 cm × 2 cm =8 cm3 The cell’s ratio of surface area to volume = 24 / 8 or 3:1 What would happen if the length of the cell triples? The cell’s surface area = 3 cm × 3 cm × 6=54 cm2 The volume = 3 cm × 3 cm × 3 cm=27 cm3 The ratio of surface area to volume = 54 / 27 or 2 : 1 Ratio of Surface Area to Volume  The ratio of surface area to volume decreased. You have less surface area (Not Good)

7. Ratio of Surface Area to Volume in Cells • As the length of a cell increases, its volume increases faster than its surface area. • The resulting decrease in the cell’s ratio of surface area to volume makes it more difficult for the cell to move needed materials in and waste products out. • How do cells fix this problem? They divide, which allows them to stay small.

8. Checkpoint Questions: 1. Give two reasons why cells divide. 2. What is the solution to the problems caused by cell growth? 3. As a cell increases in size, which increases more rapidly, its surface area or its volume? 4. Select two organelles and describe how their functions might be impaired if the cell were to become too large.

9. Ratio of Surface Area to Volume in Cells Section 10-1 Cell Size Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume Review:The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and wastes across the cell membrane. Go to Section:

10. Every cell must first copy its genetic information before cell division begins. • Each daughter cell then gets a complete copy of that information. • Cell division is called mitosis • Each cell has identical DNA

11. In eukaryotic cells, the genetic information is carried by chromosomes. Chromosomes are made up of DNA and protein. At the beginning of cell division, each chromosome consists of two identical “sister” chromatids. Each pair of chromatids is attached at an area called the centromere. Cell Division

12. Cellular Reproduction Chapter 9 The Cell Cycle • Cell division prevents the cell from becoming too large. • The cell reproduces so that you grow and heal certain injuries. • Cells reproduce by a cycle of growing and dividing called the cell cycle.

13. During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again. The Cell Cycle

14. During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again. During the M phase, mitosis(cell division) of the cell nucleus and cytokinesis takes place. The other important phase—the S phase —is the copying of the chromosomes, making a duplicate set of DNA. Between the M and S phases are G1 and G2. The G in the names of these phases stands for “gap,” but the G1 and G2 are definitely not periods when nothing takes place. They are actually periods of intense growth and activity. The Cell Cycle

15. Cellular Reproduction Chapter 9 9.1 Cellular Growth • Interphase is the stage during which the cell grows, carries out cellular functions, and replicates. • Mitosis is the stage of the cell cycle during which the cell’s nucleus and nuclear material divide. • Cytokinesisis the method by which a cell’s cytoplasm divides, creating a new cell.

16.  The Cell Cycle Section 10-2 G1 phase M phase S phase G2 phase Go to Section:

17. Cellular Reproduction Chapter 9 9.1 Cellular Growth The Stages of Interphase • The first stage of interphase, G1 • The cell is growing, carrying out normal cell functions, and preparing to replicate DNA.

18. Cellular Reproduction Chapter 9 9.1 Cellular Growth The Second Stage of Interphase, S • The cell copies its DNA in preparation for cell division.

19. Cellular Reproduction Chapter 9 9.1 Cellular Growth The Third Stage of Interphase, G2 • The cell prepares for the division of its nucleus.

20. Prophase Metaphase Anaphase Telophase Mitosis: Four Stages

21. Cellular Reproduction Chapter 9 9.2 Mitosis and Cytokinesis The Stages of Mitosis • Prophase • The cell’s chromatin tightens. • Sister chromatids are attached at the centromere. • Spindle fibers form in the cytoplasm.

22. Cellular Reproduction Chapter 9 9.2 Mitosis and Cytokinesis • The nuclear envelope seems to disappear. • Spindle fibers attach to the sister chromatids.

23. Cellular Reproduction Chapter 9 9.2 Mitosis and Cytokinesis Metaphase • Sister chromatids are pulled along the spindle apparatus toward the center of the cell. • They line up in the middle of the cell.

24. Cellular Reproduction Chapter 9 9.2 Mitosis and Cytokinesis Anaphase • The microtubules of the spindle apparatus begin to shorten. • The sister chromatids separate. • The chromosomes move toward the poles of the cell.

25. Cellular Reproduction Chapter 9 9.2 Mitosis and Cytokinesis Telophase • The chromosomes arrive at the poles and begin to relax. • Two new nuclear membranes begin to form and the nucleoli reappear. • The spindle apparatus disassembles.

26. Cytokinesis • As a result of mitosis, two nuclei—each with a duplicate set of chromosomes—are formed, usually within the cytoplasm of a single cell. • Cytokinesis: the division of the cytoplasm itself, ends mitosis. • Cytokinesis usually occurs at the same time as telophase.

27. In most animal cells the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. Each part contains its own nucleus and cytoplasmic organelles. In plants cells a structure known as the cell plate forms midway between the divided nuclei The cell plate gradually develops into a separating membrane. A cell wall then begins to appear in the cell plate. Cytokinesis

28. Cellular Reproduction Chapter 9

29. M phase (Mitosis) Interphase G1 phase S phase G2 phase Prophase Metaphase Anaphase Telophase Concept Map Section 10-2 Cell Cycle includes Cytokinesis is divided into is divided into Go to Section:

30. Bacteria and Viruses Prokaryote (Bacteria) Structure • Prokaryotes are microscopic, unicellular organisms. • They have some characteristics of all cells, such as DNA and ribosomes. • Lack a nuclear membrane and other membrane-bound organelles

31. Cell Division • In prokaryotes, the cell first replicates its genetic information before cell division begins. Then the cell splits into two parts.

32. Bacteria and Viruses Reproduction of Prokaryotes: 2 Types • Binary Fission: Division of a cell into two genetically identical cells • Conjugation: Two prokaryotes attach to each other and exchange genetic information.

33. Every cell must first copy its genetic information before cell division begins. Cell division is called mitosis Mitosis produces two genetically identical daughter cells with 2 sets of chromosomes (diploid) Mitosis Summary

34. Checkpoint Questions 1. Name the 3 main events of the cell cycle. 2. Describe what happens during each of the four phases of mitosis. 3. Describe what happens during interphase. 4. What are chromosomes made of? 5. Compare and contrast how prokaryotic and eukaryotic cells divide? 6. Compare and contrast cytokenesis in plant and animal cells.

35. What happens when mitosis goes wrong?

36. Cellular Reproduction Chapter 9 Normal Cell Cycle • Different cyclin/CDK combinations signal other activities, including DNA replication, protein synthesis, and nuclear division throughout the cell cycle.

37. Cellular Reproduction Chapter 9 Quality Control Checkpoints • The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong. • Spindle checkpoints also have been identified in mitosis.

38. Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function. Chapter 9 9.3 Cell Cycle Regulation Abnormal Cell Cycle: Cancer • Cancer is the uncontrolled growth and division of cells.

39. Cellular Reproduction Chapter 9 Causes of Cancer • The changes that occur in the regulation of cell growth and division of cancer cells are due to mutations. • Various environmental factors can affect the occurrence of cancer cells.

40. Cellular Reproduction Chapter 9 Apoptosis • Programmed cell death • Cells going through apoptosis actually shrink and shrivel in a controlled process.

41. Cellular Reproduction Chapter 9 9.3 Cell Cycle Regulation Stem Cells • Unspecialized cells that can develop into specialized cells when under the right conditions

42. Cellular Reproduction Chapter 9 Embryonic Stem Cells • After fertilization, the resulting mass of cells divides repeatedly until there are about 100–150 cells. These cells have not become specialized.

43. Cellular Reproduction Chapter 9 Adult Stem Cells • Found in various tissues in the body and might be used to maintain and repair the same kind of tissue • Less controversial because the adult stem cells can be obtained with the consent of their donor

44. Stem Cell Movie: http://learn.genetics.utah.edu/content/tech/stemcells/sctypes/