8.2 - Cell Growth & Reproduction

1. 8.2 - Cell Growth & Reproduction Cell Size Limitations most cells are small ***3 reasons: 1. Diffusion limits cell size --diffusion slows over distance --if a very large cell, it would die before oxygen reaches inner mitochondria

2. 2. A cell’s DNA content limits size --most cells have 1 nucleus with DNA (DNA makes RNA – directs protein synthesis) --Cell cannot make enough RNA to run the cell 3. Surface Area to Volume Ratio --doubling the volume does not double surface area Is a big cell better? --less surface area for diffusion --not able to diffuse enough materials to support the cell and the cell will die

3. Surface area-to-volume ratio 4 mm 4 mm 2 mm 1 mm 2 mm 1 mm 1 mm 2 mm Surface area = 6 mm2 Volume = 1 mm3 4 mm Surface area = 24 mm2 Volume = 8 mm3 • If cell size doubled, the cell would require eight times more nutrients and would have eight times more waste to excrete. Section 8.2 Summary – pages 201 - 210

4. Surface area-to-volume ratio 4 mm 4 mm 2 mm 1 mm 2 mm 1 mm 1 mm 2 mm Surface area = 6 mm2 Volume = 1 mm3 4 mm Surface area = 24 mm2 Volume = 8 mm3 • The surface area, however, would increase by a factor of only four. Section 8.2 Summary – pages 201 - 210

5. Surface area-to-volume ratio 4 mm 4 mm 2 mm 1 mm 2 mm 1 mm 1 mm 2 mm Surface area = 6 mm2 Volume = 1 mm3 4 mm Surface area = 24 mm2 Volume = 8 mm3 • The cell would either starve to death or be poisoned from the buildup of waste products. Section 8.2 Summary – pages 201 - 210

6. When do cells divide? --All the time… --Cells are constantly growing, dividing, dying, replacing, healing --Humans make 25 million new cells every second Cell Reproduction– The Role of Chromosomes --Chromosomes hold the “recipe” for each cell --Cells have specific purposes: **skin to cover & protect **Bone and Cartilage **brain to transmit impulses **Blood Cells

7. The Discovery of chromosomes Chromosomes --coloredbodies in nucleus --carriers of genetic material (DNA) --copied and passed from generation to generation --not normally visible (only in cell division) The structure of eukaryotic chromosomes --most of the time DNA is in long thin strands of invisible chromatin --before a cell divides, it coils up into visible bodies called chromosomes

8. The structure of eukaryotic chromosomes Chromosome Centromere -DNA coils around proteins called Histone H1 -forms small spheres called Nucleosomes -DNA coils to form larger structures to produce visible chromosomes Sister chromatids Supercoil within chromosome Histone H1 Continued coiling within supercoil Nucleosome DNA Section 8.2 Summary – pages 201 - 210

9. The Cell Cycle Cell cycle - sequence of growth & division in a cell’s life 1. Interphase - growth period of the cell Interphase

10. Interphase, the busiest phase of the cell cycle, is divided into three parts. • a. During the first part, the cell grows and protein production is high. Interphase Rapid growth and metabolic activity

11. b. In the 2nd part of interphase (DNA synthesis), the cell copies it’s DNA. Interphase DNA synthesis and replication

12. c. In the 3rd part of Interphase: -needed cell organelles and proteins are produced and assembled -energy for cell division is stored Interphase Cell organeles replicate and the cell prepares for division

13. 2. Mitosis – when thenucleus of a cell divides, giving each “daughter” cell identical sets of chromosomes (DNA) Mitosis

14. A Replicated Chromosome • Replication occurs during • interphase 2. Sister chromatids carry the exact same genetic information 3. The centromere holds the chromatids together

15. 1. Prophase: The first phase of mitosis • During prophase, • the chromatin coils to form visible chromosomes • the nuclear envelope and nucleolus disappear • centrioles migrate to opposite poles (animals only) • spindle fibers appear from the centrioles Spindle fibers and centrioles Disappearing nuclear envelope Doubled chromosome Section 8.2 Summary – pages 201 - 210

16. 2. Metaphase: The second stage of mitosis • During metaphase --Each chromatid attached to a separate spindle fiber at it’s centromere --Actions of the spindle fibers cause the chromosomes to move to the equator of the cell Centromere Chromosomes align at cell equator Sister chromatids Section 8.2 Summary – pages 201 - 210

17. 3. Anaphase: The third phase of mitosis • During anaphase, • the centromeres split and are pulled toward opposite poles of the cell • the sister chromatids are pulled apart into separate chromosomes Individual chromosomes

18. 4. Telophase: The 4th phase of mitosis • During telophase, • two distinct daughter cells are formed. • The daughter cells begin to separate • Chromosomes begin to uncoil • Nucleus reforms Nuclear envelope reappears Two daughter cells are formed

20. Cytokinesis (begins in telophase) • Cytoplasm begins to divide to separate the • two new nuclei into separate cells 2. Animal cells develop a cell groove where the cytoplasm is being pinched together from outside inward 3. In plants, a cell plate grows between the new nuclei, growing from the middle outward, producing new cell wall

22. Why Mitosis???? --Assured genetic continuity --Two new cells genetically identical to the parent cell --Unicellular organisms remain as single cells. --In multicellular organisms, cell growth and reproduction result in groups of cells that work together as a tissue to perform a specific function.

23. --In multicellular organisms, cell growth and reproduction results in groups of cells that work together as a tissue to perform a specific function. Ex. Muscle, bone, cartilage, and blood -- Multiple tissues combine together to form organs. Ex. Stomach, kidney, and lungs -- Multiple organs combine to form organ systems. Ex. Gastro-intestinal, cardiovascular, and nervous systems