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How Cells Reproduce

How Cells Reproduce. Chapter 9. Impacts, Issues Henrietta’s Immortal Cells. Henrietta Lacks died of cancer at age 31, but her cells ( HeLa cells) are still growing in laboratories and aiding research . 9.1 Overview Of Cell Division Mechanisms. Cell reproduction simply results in more cells

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How Cells Reproduce

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  1. How Cells Reproduce Chapter 9

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

  3. 9.1 Overview Of Cell Division Mechanisms • Cell reproduction simply results in more cells • 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

  4. Mitosis, Meiosis, And Prokaryotes • Eukaryotic cells have two reproductive processes • Mitosis copies DNA and divides a nucleus, producing two identical nuclei • Meiosis is a nuclear division that produces haploid gametes (just half normal chromosomes) for sexual reproduction • Prokaryotic cells only reproduce asexually by prokaryotic fission

  5. Comparison Of Cell Division Mechanisms

  6. 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 (the famed “double helix” structure) • After duplication that starts the process, each chromosome consists of two double strands (sister chromatids) that remain attached to each other at a centromere until late in nuclear division

  7. Chromosome To Sister Chromatids

  8. Key Points About Chromosome Structure • Chromatin, chromosome, gene, it’s all DNA but different terms are used to describe the structure and process • A chromosome consists of DNA that is wrapped around proteins (histones) and condensed • Each histone and the DNA wrapped around it make up a nucleosome, the smallest unit of structural organization in chromosomes

  9. Chromosome Structure Illustrated

  10. 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

  11. 9.2 The Cell Cycle • Cell cycle stages • A sequence of three stages (interphase, mitosis, and cytoplasmic division) through which a cell passes between one cell division and the next • Interphase is normal growth and function • Mitosis is nuclear division after replication of DNA and organelles • Cytoplasmic division is the final division into two cells from the original (duplicated) one

  12. 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 • S: Interval of DNA replication (synthesis) • G2: Interval when the cell prepares for division

  13. Interphase And 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; BUT once replication takes place, it will proceed through mitosis and cytoplasmic division • Loss of control may cause cell death or cancer (remember cancer is just unregulated cell reproduction)

  14. Mitosis And 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 or paired number) • Pairs have the same shape and information about the same traits (except sex chromosomes XY)

  15. Bipolar Spindle Separates Sister Chromatids In Animal Cells Note centrioles (poles above) not in plant cells, just animal.

  16. Mitosis Maintains Chromosome Number

  17. Fig. 9-5b, p. 145

  18. 9.2 Key Concepts:Where Mitosis Fits In 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

  19. 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 (hint: remember PMAT to refer to these stages) • But, remember that we describe these phases for ease of understanding – in reality, process goes seamlessly from one stage to the next

  20. Prophase • Prophase features • Chromosomes condense • Microtubules form a bipolar spindle • Nuclear envelope breaks up • Microtubules attach to the chromosomes • Centrosome obvious • A region near the nucleus that organizes spindle microtubules; usually includes two centrioles

  21. Metaphase And Anaphase • Metaphase • All duplicated chromosomes line up midway between the spindle poles at the “equator” • Anaphase • Microtubules separate the sister chromatids of each chromosome and pull them to opposite spindle poles

  22. Telophase • Telophase • Two clusters of chromosomes reach the spindle poles • A new nuclear envelope forms around each cluster as new cells begin final form • Two new nuclei are formed, each with the same chromosome number as the parent cell

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

  24. 9.3 Key Concepts:Stages Of Mitosis • Mitosis divides the nucleus, not the cytoplasm • Mitosis has four sequential stages: prophase, metaphase, anaphase, and telophase (PMAT) • A bipolar spindle forms; it moves the cell’s duplicated chromosomes into two parcels, which end up in two genetically identical nuclei

  25. 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 • The process of cytoplasmic division • This finally separates the two “new” cells (each really half new and half old)

  26. 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 • Plant cells • A cell plate forms midway between the spindle poles; it partitions the cytoplasm when it reaches and connects to the parent cell wall – necessary to complete the cell wall of each cell.

  27. Cytoplasmic Division ExamplesIn Animal And Plant Cells

  28. The Importance Of Timing And Completion Of Cell Cycle Events Note limb buds beginning to form on this embryo as mitosis provides the needed cells

  29. 9.4 Key Concepts:Cytoplasmic Division Summary • 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

  30. 9.5 When Control Is Lost • Sometimes, controls over cell division are lost • Cancer may be the outcome, like this cell

  31. 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 • Kinases can activate other molecules to stop the cell cycle or cause cells to die • Growth factors can activate kinases to start mitosis

  32. Checkpoint Failure And Tumors • When all checkpoint mechanisms fail, a cell loses control over its cell cycle and may form a tumor (abnormal mass of cells) in surrounding tissue • Usually one or more checkpoint gene products are missing in tumor cells • Tumor suppressor gene products inhibit mitosis • Protooncogene products stimulate mitosis

  33. Neoplasms • Neoplasms • Abnormal masses of cells that lack control over how they grow and divide • Benign neoplasms (such as ordinary skin moles) stay in one place and are not cancerous • Malignant (moving, spreading) neoplasms are cancerous and usually deadly

  34. Characteristics Of Cancer Cells • Cancers (malignant neoplasms) • Cells grow and divide abnormally; capillary blood supply to the cells may increase abnormally • Cells may have altered plasma membrane and cytoplasm; their metabolism may shift toward fermentation • Cells have altered recognition proteins and weakened adhesion; may break away and invade distant tissues (metastasis)

  35. Benign And Malignant Tumors

  36. Skin Cancer Examples a. Keep an eye on this. b. See your doctor soon. c. Leave now for your doctor without delay

  37. Fig. 9-12a, p. 151

  38. Fig. 9-12b, p. 151

  39. Fig. 9-12c, p. 151

  40. 9.5 Key Concepts:The Cell Cycle And Cancer • Built-in mechanisms monitor and control the timing and rate of normal cell division that results in additional cells as needed for growth/repair • On rare occasions, the surveillance mechanisms fail, and cell division become uncontrolled and abnormal (not needed) • Tumor formation and cancer are the outcome

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