1. Chapter 9 Cellular Reproduction

2. Main Idea – Cells grow until they reach their size limit, then they either stop growing or divide. Most cells are smaller than the. at the end of a sentence in your textbook. Why are cells so small? What are the primary stages of the cell cycle? What is interphase? What are the stages of interphase?

3. Section 9.1 Cellular Growth Cell Size Limitations The key factor that limits cell size is the ratio of its surface area to its volume. The surface area of a cell is the area covered by the plasma membrane. Remember the plasma membrane is the structure that all nutrients and wastes must pass through.

4. The volume is the space made up of the inner contents of the cell, including all organelles and cytoplasm.

5. Which cell would be able to distribute nutrients and wastes to all parts of the cell more efficiently?

6. Calculating Cell Size To calculate surface area use the formula: Length x Width x Number of Sides = surface area Small cube = 1µm x 1µm x 6 sides = 6µm 2 To calculate volume use the formula: Length x Width x Height = volume Small cube = 1µm x 1µm x 1µm = 1µm 3 The ratio of surface area to volume is 6:1

7. Medium cube Surface area = 2µm x 2µm x 6 = 24µm 2 Volume = 2µm x 2µm x 2µm = 8µm 3 Medium cube ratio = 3:1 This is a smaller ratio of surface area to volume. This means the cell might have a harder time supplying nutrients and expelling wastes products.

8. What is your prediction for the largest cube? Large cube Your turn Surface area = ? Volume = ? Ratio = ?

9. Large cube calculations Surface area = 4µm x 4µm x 6 = 96µm 2 Volume = 4µm x 4µm x 4µm = 64µm 3 Ratio = 1.5:1 Does the nucleus seem to change size? Would the other organelles change size? Which cell above would be the most efficient?

10. Another reason cells stay small is to transport substances more efficiently. - Substances move by diffusion or by motor proteins. -Diffusion over large distances is slow and inefficient. - Small cells maintain more efficient transport systems.

11. Another reason cells stay small is to communicate more efficiently.  Cell size affects the cell’s ability to communicate instructions for cellular functions.  If a cell becomes too large, it becomes almost impossible for cellular communications. Example: The signal to trigger protein synthesis might not reach the ribosome fast enough in large cells to make protein to keep the cell alive.

12. The Cell Cycle - Once a cell reaches its size limit it will stop growing or divide. Cells reproduce by a cycle of growing and dividing called the cell cycle. Most cells will divide. Cell division prevents the cell from becoming too large. It also is the way the cell reproduces so that you grow and heal certain injuries.

13. 3 Main stages of the cell cycle Stage 1 – Interphase Interphase is divided up into 3 substages. G 1, S, G 2 - cell grows (G 1 ) - carries out cell functions (S) - replicates (G 2 ) (makes copies of its DNA)

14. The 3 Stages of interphase G 1 (stage 1) - the cell is growing, - carrying out normal cell functions - preparing to duplicate DNA

15. S (stage 2) - Cell copies its DNA - Prepares for cell division The 3 Stages of interphase

16. Genetic material is replicated (S) Chromatin is the relaxed form of DNA in a cell’s nucleus. Chomosomes are structures that contain the genetic material that is passed from generation to generation.

17. Sister chromatids Chromosomes Shape: - Chromatin coil around histones - 2 identical halves = sister chromatids - Held together with a centromere.

18. The 3 Stages of interphase G 2 (stage 3) - Cell prepares for the division of its nucleus. - The cell checks to make sure everything is ready to go on to mitosis.

19. Stage 2 - Mitosis During mitosis the cell’s nucleus and nuclear material divide. Mitosis is divided up into 4 substages.

20. Stage 3 - Cytokinesis During cytokinesis a cell’s cytoplasm divides, creating a new cell. Some cells complete the cycle as fast as 8 minutes. Some cells take a year to complete the cycle. Most animal cells take 24 hours to complete the cell cycle.

21. Section 9.2 Mitosis and Cytokinesis Main Idea: Eukaryotic cells reproduce by mitosis, the process of nuclear division, and cytokinesis of cytoplasm division.

22. Mitosis – Why is it important? The key activity of mitosis is to accurately separate the cell’s duplicated DNA. Why? 1. Genetic information is passed into new cells. 2. genetically identical daughter cells are made. (same DNA, cytoplasm and organelles as parent cell) 3. Increases the number of cells so young organisms can grow to its adult size. -4. Organisms can replace damaged cells.

23. Four Stages of Mitosis 1. Prophase - 3 phases early -nucleoi break down middle nuclear membrane break down late centrioles on opposite sides 2. Metaphase 3. Anaphase 4. Telophase

24. Prophase – The 1 st stage -Longest stage of mitosis -Chromatin tightens into chromosomes -Chromosome contains genetic material -Each half of the X is a Sister Chromatid -Sister Chromatids are structures that contain identical copies DNA. -Centromere is where sister chromatids are attached at the center.

25. Spindle Apparatus is important for moving and organizing chromsomes before cell division. 1. Nucleolus seems to disappear 2. Spindle fibers form in cytoplasm (microtubules) 3. Centrioles migrate to the ends or poles of the cell. 4. Aster fibers appear at the centrioles During middle prophase….

26. Near the end of prophase… - Nuclear envelope seems to disappear - Spindle fibers attach to each side of sister chromatids - Spindle fibers attach at each pole of the cell. If the cell were to divide now, where do you predict it would split?

27. Metaphase is the 2 nd stage of mitosis One of the shortest stages 1. Sister chromatids are pulled by motor proteins toward the center of the cell 2. Chromatids line up in the middle or equator of the cell.

28. Anaphase – the 3 rd stage of mitosis Chromatids are pulled apart during anaphase. 1. Microtubules shorten and pull apart at the centomere 2. Sister chromatids separate into 2 identical chromosomes 3. Chromosomes move towards the poles of the cell.

29. Telophase – 4 th stage of mitosis The stage when chromosomes arrive at the poles of the cell. 1. Chromosomes relax back into chromatin 2. Two new nuclear membranes start to form 3. nucleoli reappear 4. spindle apparatus disassembles

30. Cytokinesis…the division of cytoplasm In animals 1. Microfilaments will constrict to pinch off cytoplasm to form a groove. 2. will result in 2 cells with identical nuclei In plants 1. a cell plate forms between the 2 daughter nuclei 2. cell wall then forms 3. two genetically identical cells are formed

31. Cells alive www.cellsalive.comwww.cellsalive.com

32. Section 9.3 Cell Cycle Regulation Main Idea: Normal Cell Cycle The timing and rate of cell division is important to healthy cells. The rate of cell division depends on the type of cell. The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong.

33. Types of cells All somatic (body cells) have the same number of chromosomes. (46) 2n Body cells are called diploid as they have 2 copies of each chromosome. (di = 2) All gametes (sex cells) have half the number of chromosomes (23) n Sex Cells are called haploid as they have half the number of chromosomes.

34. Apoptosis – programmed cell death Not all cells are destined to survive. Example: Human development- Hands and Feet of embryo Cells between fingers and toes undergo apoptosis. When it is time to separate fingers and toes in the organism. Cells shrivel and shrink to be disposed of by the cell.

35. Example of Problem with Apoptosis: Web Fingers

36. Protecting normal cell growth Apoptosis also occurs when… -Cells have been damaged beyond repair -DNA has been damaged that could lead to cancer -In plants apoptosis is what causes leaves to fall from the trees.

37. Cancer.. uncontrolled cell growth and division of cells When the normal control mechanisms in a cell fails, cancer can result. Cancer cells can be identified because they have an abnormal shape compared to the normal cell. Left unchecked, a cancerous tumor can destroy its host organism.

38. More about Cancer Cancer occurs due to mutations or changes in the segments of DNA that controls the production of proteins. Often the genetic change or damage is repaired by the cell’s repair system. Environmental Factors can affect cells. Carcinogens are substances that are known to cause cancer. Avoiding carcinogens can help reduce the risk of cancer.

39. Carcinogens are substances that are known to cause cancer. Avoiding carcinogens can help reduce the risk of cancer. Lung cancer can result from 1 and 2 at the right. Is lung cancer passed on in cells by genetic material? Known Carcinogens 1)Tobacco products: -first hand smoke (smoking) -second hand smoke -smokeless tobacco 2) Asbestos Ultraviolet radiation (sun) X-ray radiation Harmful chemicals

40. Cancer genetics More than one change in DNA is needed in a normal cell to cause cancer. Over time, there might be many changes in DNA This might explain why the risk of cancer increases with age. An offspring that inherits one or more changes from a parent may be at a higher risk for developing cancer.

41. Stem Cells are unspecialized cells that can develop into specialized cells under the right conditions. Because stem cells are not locked into becoming a certain cell, they might be the key to curing many medical conditions and genetic defects.

42. Prokaryotic Cells divide by Binary Fission