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Chapter 11 How Cells Reproduce (Sections 11.1 - 11.3)

Chapter 11 How Cells Reproduce (Sections 11.1 - 11.3). 11.1 Henrietta’s Immortal Cells. Henrietta Lacks died of cancer at age 31 50 years later, her cells still live in laboratories around the world Most human cells grown in laboratories die within a few weeks.

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Chapter 11 How Cells Reproduce (Sections 11.1 - 11.3)

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  1. Chapter 11How Cells Reproduce (Sections 11.1 - 11.3)

  2. 11.1 Henrietta’s Immortal Cells • Henrietta Lacks died of cancer at age 31 • 50 years later, her cells still live in laboratories around the world • Most human cells grown in laboratories die within a few weeks

  3. 11.2 Multiplication by Division • Cells reproduce by dividing • Division of a eukaryotic cell typically occurs in two steps: nuclear division followed by cytoplasmic division • The sequence of stages through which a cell passes during its lifetime is called the cell cycle

  4. The Life of a Cell • One cell cycleconsists of three phases: interphase, mitosis, and cytoplasmic (cell) division • cell cycle • A series of events from the time a cell forms until its cytoplasm divides

  5. Eukaryotic Cell Cycle

  6. Eukaryotic Cell Cycle G1 is the interval of growth before DNA replication. The cell’s chromosomes are unduplicated during this stage. S is the time of synthesis. The name refers to DNA synthesis, because the cell copies its DNA during this Stage. 1 2 At the end of mitosis, the cytoplasm typically divides, and the cycle begins anew in interphase for each descendant cell. 6 G2 is the interval after DNA replication and before mitosis. The cell prepares to divide during this stage. 3 5 4 The nucleus divides during mitosis. Interphase ends. Fig. 11.2, p. 164

  7. ANIMATION: The cell cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

  8. Introduction to Interphase • A typical cell spends most of its life in interphase • interphase • Interval between mitotic divisions when a cell grows, doubles the number of its cytoplasmic components, and replicates its DNA in preparation for division • Consists of three stages: G1, S, and G2

  9. Three Stages of Interphase • G1: The first interval (or gap) of cell growth • The time before DNA replication when cells engage in their metabolic business • S: The time of synthesis (DNA replication) when the cell prepares to divide • G2: The second interval (or gap) when the cell makes proteins that will drive cell division

  10. Introduction to Mitosis • The nucleus divides during mitosis, producing an identical copy of its set of chromosomes • mitosis • Nuclear division mechanism that maintains the chromosome number • Basis of body growth and tissue repair in multicelled eukaryotes; also asexual reproduction in some plants, animals, fungi, and protists

  11. Homologous Chromosomes • Human diploid cells have two sets of chromosomes: 46 chromosomes in 23 pairs • Except for a pairing of sex chromosomes (XY) in males, the chromosomes of each pair are homologous • homologous chromosomes • Chromosomes with the same length, shape, and set of genes

  12. Introduction to Cytoplasmic Division • When the cytoplasm divides, the new nuclei produced by mitosis are packaged into separate cells • Each new cell has a full complement of unduplicated chromosomes, and each starts the cell cycle over again in G1 of interphase

  13. Mitosis Maintains Chromosome Number

  14. Mitosis Maintains Chromosome Number A An unduplicated pair of chromosomes in a cell in G1. B By G2, each chromosome has been duplicated. C Mitosis and cyto-plasmic division package one copy of each chromosome into each of two new cells. Fig. 11.3, p. 165

  15. A An unduplicated pair of chromosomes in a cell in G1. B By G2, each chromosome has been duplicated. C Mitosis and cyto-plasmic division package one copy of each chromosome into each of two new cells. Mitosis Maintains Chromosome Number Stepped Art Fig. 11.3, p. 165

  16. A Bigger Picture of Cell Division • Mitosis and cytoplasmic division increase body size during development and replace damaged or dead cells • Many species of plants, animals, fungi, and protists reproduce by asexual reproduction using mitosis and cytoplasmic division • asexual reproduction • Reproductive mode by which offspring arise from a single parent only

  17. Cell Division and Development • Frog embryos after three mitotic divisions of a fertilized egg

  18. Key Concepts • 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 cycle proceeds through intervals of interphase, mitosis, and cytoplasmic division

  19. 11.3 Mitosis • During interphase, a chromosomes are loosened to allow transcription and DNA replication • When mitosis begins, duplicated DNA packs tightly together into chromosome shapes

  20. The Four Stages of Mitosis • 1. prophase • Stage of mitosis during which chromosomes condense and become attached to a newly forming spindle • 2. metaphase • Stage of mitosis at which the cell’s chromosomes are aligned midway between poles of the spindle

  21. The Four Stages of Mitosis • 3. anaphase • Stage of mitosis during which sister chromatids separate and move to opposite spindle poles • 4. telophase • Stage of mitosis during which chromosomes arrive at the spindle poles and decondense, and new nuclei form

  22. Centrosomes and Spindles • Most animal cells have a centrosome, a region with two centrioles that gets duplicated just before prophase • During prophase, one of the two centrosomes moves to the opposite side of the cell, and microtubules extend from both centrosomes to form a spindle • spindle • Dynamically assembled and disassembled network of microtubules that moves chromosomes during nuclear division

  23. Mitosis: Prophase • Early Prophase • Mitosis begins: DNA starts to condense • The centrosome gets duplicated • Prophase • Duplicated chromosomes become visible • One of the two centrosomes moves to the opposite side of the nucleus • The nuclear envelope breaks up

  24. Mitosis: Prophase • Early prophase • Prophase

  25. Mitosis: Metaphase • Transition to Metaphase • Nuclear envelope is gone; chromosomes are at their most condensed • Spindle microtubules assemble and bind to chromosomes at the centromere • Sister chromatids are attached to opposite spindle poles • Metaphase • Chromosomes are aligned midway between spindle poles

  26. Mitosis: Metaphase • Transition to Metaphase • Metaphase

  27. Mitosis: Anaphase and Telophase • Anaphase • Spindle microtubules separate the sister chromatids and move them toward opposite spindle poles • Each sister chromatid is now an individual, unduplicated chromosome • Telophase • Chromosomes reach the spindle poles and decondense • A nuclear envelope forms around each cluster, and mitosis ends

  28. Mitosis: Anaphase and Telophase • Anaphase • Telophase

  29. Mitosis: Prophase Fig. 11.5.1-3, p. 167

  30. Mitosis: Prophase centrosome Early Prophase Mitosis begins. In the nucleus, the DNA begins to appear grainy as it starts to condense. The centrosome gets duplicated. 1 Prophase The duplicated chromosomes become visible as they condense. One of the two centrosomes moves to the oppositeside of the nucleus. The nuclear envelope breaks up. 2 Transition to Metaphase The nuclear envelope is gone, and the chromosomes are at their most condensed. Spindle microtubules assemble and bind to chromosomes at the centromere. Sister chromatids are attached to opposite spindle poles. 3 microtubule of spindle Fig. 11.5.1-3, p. 167

  31. Mitosis: Prophase Fig. 11.5.4-6, p. 167

  32. Mitosis: Prophase Metaphase All of the chromosomes are aligned midway between the spindle poles. 4 Anaphase Spindle microtubules separate the sister chromatids and move them toward opposite spindle poles. Each sister chromatid has now become an individual, unduplicated chromosome. 5 Telophase The chromosomes reach the spindle poles and decondense. A nuclear envelope forms around each cluster, and mitosis ends. 6 Fig. 11.5.4-6, p. 167

  33. Animation: Mitosis

  34. Animation: Mitosis

  35. Key Concepts • Mitosis • Mitosis divides the nucleus and maintains the chromosome number • It has four sequential stages: prophase, metaphase, anaphase, and telophase • A spindle parcels the cell’s duplicated chromosomes into two nuclei

  36. ANIMATION: Mitosis-Step-by-Step To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

  37. ANIMATION: Chromosome choreography To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

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