How Cells Reproduce

1. How Cells Reproduce Chapter 9 Hsueh-Fen Juan Oct. 16, 2012

2. Video: Henrietta's immortal cells

3. Impacts, IssuesHenrietta’s Immortal Cells • Henrietta Lacks died of cancer at age 31, but her cells (HeLa cells) are still growing in laboratories

4. 9.1 Overview of Cell Division Mechanisms • Individual cells or organisms produce offspring by the process of reproduction • When a cell reproduces, each descendent receives information coded in DNA, and enough cytoplasm to begin operating • 細胞分裂包含：1.細胞核分裂(mitosis or meiosis) 2.細胞質分裂

5. Mitosis, Meiosis, and the Prokaryotes • Eukaryotic cells • Mitosis copies DNA and divides a nucleus, producing two identical nuclei • Meiosis is a nuclear division that produces haploid gametes for sexual reproduction • (有絲、減數都是在討論細胞核的分裂，非細胞質) • Prokaryotic cells reproduce asexually by prokaryotic fission (原核裂變，和有絲、減數分裂相比，機制上完全不同)

6. Comparison of Cell Division Mechanisms

7. Key Points About Chromosome Structure • Each species has a characteristic number of chromosomes that differ in length and shape • Each consists of one double strand of DNA • After duplication, each consists of two double strands (sister chromatids) that remain attached to each other at a centromere until late in nuclear division • Chromatid: 染色分體 (chromosome: 染色體) Centromere: 著絲點 (centrosome: 中心體)，其上 的 binding sites 稱 kinetochore (著絲粒)

8. A Chromosome and Sister Chromatids

9. Key Points About Chromosome Structure • A chromosome consists of DNA that is wrapped around proteins (histones 組織蛋白) and condensed • Each histone and the DNA wrapped around it make up a nucleosome (核小體), the smallest unit of structural organization in eukaryotic chromosomes

10. B When a chromosome is at its most condensed, the DNA is packed into tightly coiled coils. centromere multiple levels of coiling of DNA and proteins C When the coiled coils unwind, a molecule of chromosomal DNA and its associated proteins are organized as a cylindrical fiber. A Duplicated human chromosome in its most condensed form. If this chromosome were actually the size shown in the micrograph, its two DNA strands would stretch out about 800 meters (0.5 miles). fiber D A loosened fiber shows a “beads-on-a-string” organization. The “string” is the DNA molecule; each “bead” is one nucleosome. beads on a string DNA double helix core of histones E A nucleosome consists of part of a DNA molecule looped twice around a core of histone proteins. nucleosome Chromosome Structure Stepped Art Fig. 9-3 (b-e), p. 143

11. Animation: Chromosome structural organization

12. G1 S Interval of cell growth and activity before DNA replication (chromosomes unduplicated) Interval of cell growth when the DNA is replicated (all chromosomes are duplicating) G2 Interval after DNA replication; the cell prepares to divide (Cells make the proteins that will drive mitosis) cytoplasmic division; each descendant cell enters interphase The cell cycle Telophase G2 Anaphase Metaphase Prophase Interphase ends for parent cell Stepped Art Fig. 9-4, p. 144

13. Animation: The cell cycle

14. 9.1 Key Concepts:Chromosomes and Dividing Cells • Individuals have a characteristic number of chromosomes in each of their cells • The chromosomes differ in length and shape, and they carry different portions of the cell’s hereditary information • Division mechanisms parcel out the information into descendent cells

15. 9.2 Introducing the Cell Cycle • Cell cycle • A sequence of three stages (interphase, mitosis, and cytoplasmic division) through which a cell passes between one cell division and the next

16. Interphase • Interphase consists of three stages, during which a cell increases in size, doubles the number of cytoplasmic components, and duplicates its DNA • G1: Interval of cell growth and activity，(DNA未複製) • S: Interval of DNA replication (synthesis，DNA複製中) • G2: Interval when the cell prepares for division. Cells make the proteins that will drive mitosis. (DNA已完成複製)

17. Interphase and the Life of a Cell • Most cell activities take place during G1 • Control mechanisms work at certain points in the cell cycle; some can keep cells in G1(例：神經細胞大多永遠停於G1，因此不分裂) • Loss of control may cause cell death or cancer(例：強制使神經細胞跳脫G1會使其死亡，而非細胞分裂，因為它有控制機制使其在cell cycle失控時self-destruct)

18. Mitosis and the Chromosome Number • Mitosis produces two diploid nuclei with the same number and kind of chromosomes as the parent • Chromosome number • The sum of all chromosomes in a type of cell • Human cells have 46 chromosomes paired in 23 sets (diploid number，二倍體) • Pairs have the same shape and information about the same traits (except sex chromosomes XY)

19. Mitosis and the Chromosome Number • Bipolar spindle (雙極紡錘絲) • A dynamic network of microtubules that forms during nuclear division • Grows into the cytoplasm from opposite poles of the cell and attaches to duplicated chromosomes • Microtubules from opposite poles attach to different sister chromatids and separate them

20. Bipolar Spindle Separates Sister Chromatids

21. Mitosis Maintains Chromosome Number

22. 9.2 Key Concepts:Where Mitosis Fits in the Cell Cycle • A cell cycle starts when a new cell forms by division of a parent cell, and ends when the cell completes its own division • A typical cell proceeds through intervals of interphase, mitosis, and cytoplasmic division

23. 9.3 A Closer Look at Mitosis • When a nucleus divides by mitosis, each new nucleus has the same chromosome number as the parent cell • There are four main stages of mitosis: prophase, metaphase, anaphase, and telophase

24. Prophase • Prophase • Chromosomes condense • Microtubules form a bipolar spindle with motor proteins traveling along them (消耗ATP) • Nuclear envelope breaks up • Microtubules attach to the chromosomes • 中心體在前期之前(early prophase)即完成複製 • 植物細胞無中心體，但有其他構造控制紡錘絲 • Centrosome • A region near the nucleus that organizes spindle microtubules; usually includes two centrioles (中心體通常含兩個中心粒)

25. Metaphase and Anaphase • Metaphase • All duplicated chromosomes line up midway between the spindle poles by adding and losing tubulin subunits to grow or shrink microtubules. • Anaphase • Microtubules separate the sister chromatids of each chromosome and pull them to opposite spindle poles • 3 cell activities bring this about: • 連接在染色分體上的紡錘絲微管縮短 • 機動蛋白把染色分體拖往紡錘絲微管縮短的方向 • 在赤道板上重疊的微管也彼此滑動縮短

26. Telophase • Telophase • Two clusters of chromosomes reach the spindle polesand decondense • A new nuclear envelope forms around each cluster • New plasma membrane may assemble • Two new nuclei are formed, each with the same chromosome number as the parent cell

27. Mitosis

28. Fig. 9-6 (2), p. 147

29. Fig. 9-6 (2a), p. 147

30. Fig. 9-6 (2b), p. 147

31. Fig. 9-6 (2c), p. 147

32. Fig. 9-6 (2d), p. 147

33. Fig. 9-6 (2e), p. 147

34. Fig. 9-6 (2f), p. 147

35. Animation: Mitosis-step-by-step

36. Animation: Mechanisms for chromosome movement

37. 9.3 Key Concepts:Stages of Mitosis • Mitosis divides the nucleus, not the cytoplasm • Mitosis has four sequential stages: prophase, metaphase, anaphase, and telophase • A bipolar spindle forms; it moves the cell’s duplicated chromosomes into two parcels, which end up in two genetically identical nuclei

38. 9.4 Cytoplasmic Division Mechanisms • In most kinds of eukaryotes, the cell cytoplasm divides between late anaphase and the end of telophase, but the mechanism of division differs • Cytokinesis (aka cytoplasmic division) • The process of cytoplasmic division

39. Cytoplasmic Division in Animal and Plant Cells • Animal cells • A contractile ring partitions the cytoplasm • A band of actin filaments rings the cell midsection, contracts, and pinches the cytoplasm in two(The indentation is called Cleavage furrow注意) • Plant cells • The plane of division is established by microtubules and actin filaments that formed and broke up before mitosis began • A cell plate forms midway between the spindle poles; it partitions the cytoplasm when it reaches and develop into primary cell wall merging with the parent cell wall

40. Cytoplasmic Division in Animal and Plant Cells

41. Fig. 9-7a, p. 148

42. Fig. 9-7b, p. 148

43. Animation: Cytoplasmic division

44. 9.4 Key Concepts:How the Cytoplasm Divides • After nuclear division, the cytoplasm divides • One nucleus ends up in each of two new cells • In animal cells, the cytoplasm pinches in two • In plant cells, a cross-wall forms in the cytoplasm and divides it

45. 9.5 When Control is Lost • Sometimes, controls over cell division are lost • Cancer may be the outcome

46. Cell Cycle Controls • Checkpoints in the cell cycle allow problems to be corrected before the cycle advances • Proteins produced by checkpoint genes interact to advance, delay, or stop the cell cycle (when DNA’s not copied completely, damaged, or the nutrient is not sufficient to support cell growth) • Kinases can activate other molecules to stop the cell cycle or cause cells to die • Growth factors can activate kinases (by binding to receptors on target cell) to activate genes that stimulate cells to start mitosis

47. Protein Products of Checkpoint Genes in Action 53BP1 BRCA1

48. Checkpoint Failure and Tumors • When all checkpoint mechanisms fail, a cell loses control over its cell cycle and may form a tumor (abnormal mass) in surrounding tissue • Usually one or more checkpoint gene products are missing in tumor cells • Checkpoint gene products (protein) that inhibit mitosis are called Tumor suppressors (腫瘤抑制物) • Checkpoint genes encoding proteins that stimulate mitosis are called Protooncogenes (原癌基因)

49. Neoplasms • Neoplasms (腫瘤) • Abnormal masses of cells that lack control over how they grow and divide • Benign (noncancerous 良性) neoplasms, such as ordinary skin moles, stay in one place and are not cancerous • Malignant (cancerous 惡性) neoplasms are cancerous

50. Characteristics of Cancer Cells • Cancers (malignant neoplasms) • Cells grow and divide abnormally; capillary blood supply to the cells may increase abnormally (微血管暴量，供血異常暴增) • Cells may have altered plasma membrane and cytoplasm: Membrane may be leaky and missing proteins; Cytoskeleton may be shrunken or disorganized; Metabolism may shift toward fermentation from aerobic respiration(超級瘋狂) • Cells have altered recognition proteins and weakened adhesion; may break away and invade distant tissues (metastasis 轉移)