Chapter 11 The Continuity of Life: Cellular Reproduction 11.1 What is the role of cellular reproduction in the lives of individual cells & entire organism? 11.2 How is DNA in eukaryotic cells organized into chromosomes 11.3 How do cells reproduce by mitotic cell division 11.4 How is the cell cycle controlled?

Chapter 11 The Continuity of Life: Cellular Reproduction 11.5 What do so many organisms reproduce sexually? 11.6 How does meiotic cell division produce haploid cells? 11.7 How do mitotic and meiotic cell division occur in the life cycle of eukaryotes? 11.6 How do meiosis and sexual reproduction produce genetic variability?

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual Cells and Entire Organisms? Sexual reproduction is the union of gametes (like a sperm and egg) Asexual reproduction is just one parent dividing Cell division in eukaryotes enables asexual reproduction

Figure: 11-1 part a Title: Cell division in eukaryotes enables asexual reproduction part a Caption: (a) In unicellular microorganisms, such as the protist Paramecium, cell division produces two new, independent organisms.

Figure: 11-1 part b Title: Cell division in eukaryotes enables asexual reproduction part b Caption: (b) Yeast, a unicellular fungus, reproduces by cell division.

bud Figure: 11-1 part c Title: Cell division in eukaryotes enables asexual reproduction part c Caption: (c) Hydra, a freshwater relative of the sea anemone, grows a miniature replica of itself (a bud) on its side. When fully developed, the bud breaks off and assumes independent life.

Figure: 11-1 part d Title: Cell division in eukaryotes enables asexual reproduction part d Caption: (d) Trees in an aspen grove are often genetically identical. Each tree grows up from the roots of a single ancestral tree. This photo shows three separate groves near Aspen, Colorado. In fall, the appearance of their leaves shows the genetic identity within a grove and the genetic difference between groves.

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual Cells and Entire Organisms? The prokaryotic cell cycle consists of growth and binary fission Binary fission means splitting in two Creates 2 identical cells except for mutations (caused by copying mistakes)

FIGURE 11-2a The prokaryotic cell cycle (a) The prokaryotic cell cycle consists of growth and DNA replication, followed by binary fission.

FIGURE 11-2b The prokaryotic cell cycle (b) Binary fission in prokaryotic cells.

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual Cells and Entire Organisms? The eukaryotic cell cycle consists of interphase and cell division Often cells only divide when they receive signals, such as growth hormones Some never divide, like muscle and nerve cells

FIGURE 11-3 The eukaryotic cell cycle The eukaryotic cell cycle consists of interphase and mitotic cell division. Some cells enter the G0 phase and may not divide again.

11.1 What Is the Role of Cellular Reproduction in the Lives of Individual Cells and Entire Organisms? There are two types of cell division in eukaryotic cells: Mitotic cell division –> produces two daughter cells that are genetically identical with the same number of chromosomes Meiotic cell division -> produces four daughter cells with half the chromosomes (gametes)

differentiation, and growth baby mitosis, differentiation, and growth mitosis, differentiation, and growth baby meiosis in ovaries embryo meiosis in testes egg mitosis, differentiation, and growth fertilized egg sperm Figure: 11-4 Title: Mitotic and meiotic cell division in the human life cycle Caption: Within ovaries, meiotic cell division produces eggs; within testes, meiotic cell division produces sperm. Fusion of egg and sperm produce a fertilized egg that develops into an adult by numerous mitotic cell divisions and differentiation of the resulting cells. fertilization

Section 11.2 Outline 11.2 How Is DNA in Eukaryotic Cells Organized into Chromosomes? The Eukaryotic Chromosome Consists of a DNA Double Helix Bound to Proteins Eukaryotic Chromosomes Usually Occur in Homologous Pairs with Similar Genetic Information A Karyotype Reveals Chromosomal Types and Ploidy

DNA wrapped around histone proteins (10 nm diameter) DNA (2 nm diameter) Figure: 11-5 top Title: Chromosome structure top Caption: A eukaryotic chromosome contains a single, linear DNA double helix (top), which, in humans, is about 14 to 73 millimeters (mm) long and 2 nanometers (nm) in diameter. The DNA is wound around proteins called histones, forming nucleosomes (middle); this reduces the length by about a factor of 6. Other proteins coil up adjacent nucleosomes, much like a Slinky toy, reducing the length by another factor of 6 or 7. The coils of DNA and their associated proteins are attached in loops to still larger coils of protein "scaffolding" to complete the chromosome (bottom). All of this wrapping, coiling, and looping makes the extended interphase chromosome roughly 1000 times shorter than the DNA molecule it contains. Still other proteins produce about another 10-fold condensation during cell division (see Fig. 11-6). histone proteins nucleosome: DNA wrapped around histone proteins (10 nm diameter)

coiled nucleosomes (30 nm diameter) chromosome: coils gathered onto protein scaffold (200 nm diameter) protein scaffold Figure: 11-5 bottom Title: Chromosome structure bottom Caption: A eukaryotic chromosome contains a single, linear DNA double helix (top), which, in humans, is about 14 to 73 millimeters (mm) long and 2 nanometers (nm) in diameter. The DNA is wound around proteins called histones, forming nucleosomes (middle); this reduces the length by about a factor of 6. Other proteins coil up adjacent nucleosomes, much like a Slinky toy, reducing the length by another factor of 6 or 7. The coils of DNA and their associated proteins are attached in loops to still larger coils of protein "scaffolding" to complete the chromosome (bottom). All of this wrapping, coiling, and looping makes the extended interphase chromosome roughly 1000 times shorter than the DNA molecule it contains. Still other proteins produce about another 10-fold condensation during cell division (see Fig. 11-6). DNA coils

DNA (2 nm diameter) histone proteins nucleosome: DNA wrapped around Figure: 11-5 Title: Chromosome structure Caption: A eukaryotic chromosome contains a single, linear DNA double helix (top), which, in humans, is about 14 to 73 millimeters (mm) long and 2 nanometers (nm) in diameter. The DNA is wound around proteins called histones, forming nucleosomes (middle); this reduces the length by about a factor of 6. Other proteins coil up adjacent nucleosomes, much like a Slinky toy, reducing the length by another factor of 6 or 7. The coils of DNA and their associated proteins are attached in loops to still larger coils of protein "scaffolding" to complete the chromosome (bottom). All of this wrapping, coiling, and looping makes the extended interphase chromosome roughly 1000 times shorter than the DNA molecule it contains. Still other proteins produce about another 10-fold condensation during cell division (see Fig. 11-6). coiled nucleosomes (30 nm diameter) chromosome: coils gathered onto protein scaffold (200 nm diameter) protein scaffold DNA coils

genes centromere telomeres Figure: 11-UN1 Title: Chromosome

centromere means middle body duplicated chromosome (2 DNA double helices) sister chromatids Figure: 11-UN2 Title: Duplicated chromosome centromere means middle body

sister chromatids centromere Figure: 11-6 Title: Human chromosomes during mitosis Caption: The DNA and associated proteins in these duplicated human chromosomes have coiled up into the thick, short sister chromatids attached at the centromere. Each visible strand of “texture” is a loop of DNA. During cell division, the condensed chromosomes are about 5 to 20 micrometers long. At other times, the chromosomes uncoil until they are about 10,000 to 40,000 micrometers long. sister chromatids centromere

independent daughter chromosomes, each with one identical DNA double helix Figure: 11-UN3 Title: Daughter chromosomes

autosomes sex chromosomes Figure: 11-7 Title: The karyotype of a human male Caption: Staining and photographing the entire set of duplicated chromosomes within a single cell produces a karyotype. Pictures of the individual chromosomes are cut out and arranged in descending order of size. The chromosome pairs (homologues) are similar in both size and staining pattern and have similar genetic material. Chromosomes 1 through 22 are the autosomes; the X and Y chromosomes are the sex chromosomes. Notice that the Y chromosome is much smaller than the X chromosome. If this were a female karyotype, it would have two X chromosomes. sex chromosomes

11.2 How Is DNA in Eukaryotic Cells Organized into Chromosomes? Eukaryotic chromosomes usually occur in homologous pairs with similar genetic information Cells with pairs of homologous chromosomes are called diploid for double. (2n) Gametes are haploids for half. (1n)

Section 11.3 Outline 11.3 How Do Cells Reproduce by Mitotic Cell Division? Mitosis Consists of Four Phases Events of Mitotic Prophase Events of Mitotic Metaphase Events of Mitotic Anaphase Events of Mitotic Telophase Cytokinesis

FIGURE 11-3 The eukaryotic cell cycle The eukaryotic cell cycle consists of interphase and mitotic cell division. Some cells enter the G0 phase and may not divide again.

Duplicated chromosomes in relaxed state; duplicated centrioles remain clustered. INTERPHASE nuclear envelope chromatin nucleolus Figure: 11-8 left part a Title: Mitotic cell division in an animal cell left part a LATE INTERPHASE Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? centriole pairs LATE INTERPHASE

Chromosomes condense and shorten; spindle microtubules begin to form between separating centriole pairs. MITOSIS condensing chromosomes Figure: 11-8 left part b Title: Mitotic cell division in an animal cell left part b EARLY PROPHASE Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? beginning of spindle formation EARLY PROPHASE

of each sister chromatid. Nucleolus disappears; nuclear envelope breaks down; spindle microtubules attach to the kinetochore of each sister chromatid. pole Figure: 11-8 left part c Title: Mitotic cell division in an animal cell left part c LATE PROPHASE Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? kinetochore pole LATE PROPHASE

Kinetochores interact; spindle microtubules line up chromosomes at cell's equator. spindle microtubules Figure: 11-8 left part d Title: Mitotic cell division in an animal cell left part d METAPHASE Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? METAPHASE

Sister chromatids separate and move to opposite poles of the cell; spindle microtubules push poles apart. "free" spindle fibers Figure: 11-8 right part e Title: Mitotic cell division in an animal cell right part e ANAPHASE Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? ANAPHASE

reaches each pole and relaxes into extended state; nuclear One set of chromosomes reaches each pole and relaxes into extended state; nuclear envelopes start to form around each set; spindle microtubules begin to disappear. chromosomes extending nuclear envelope re-forming Figure: 11-8 right part f Title: Mitotic cell division in an animal cell right part f TELOPHASE Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? TELOPHASE

Cell divides in two; each daughter cell receives one nucleus and about half of the cytoplasm. Figure: 11-8 right part g Title: Mitotic cell division in an animal cell right part g CYTOKINESIS Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? CYTOKINESIS

Spindles disappear, intact nuclear envelopes form, chromosomes extend completely, and the nucleolus reappears. Figure: 11-8 right part h Title: Mitotic cell division in an animal cell right part h INTERPHASE OF DAUGHTER CELLS Caption: Question What would the consequences be if one set of sister chromatids failed to separate at anaphase? INTERPHASE OF DAUGHTER CELLS

Cytokinesis in an Animal Cell Microfilaments form a ring around the cell's equator. The microfilament ring contracts, pinching in the cell's “waist.” The waist completely pinches off, forming two daughter cells. Figure: 11-9 part a Title: Cytokinesis in an animal cell part a Caption: (a) A ring of microfilaments just beneath the plasma membrane contracts around the equator of the cell, pinching it in two.

Cytokinesis in an Plant Cell cell wall Golgi complex plasma membrane carbohydrate- filled vesicles Carbohydrate-filled vesicles bud off the Golgi complex and move to the equator of the cell. Vesicles fuse to form a new cell wall (red) and plasma membrane (yellow) between daughter cells. Complete separation of daughter cells. Figure: 11-10 Title: Cytokinesis in a plant cell

Section 11.4 Outline 11.4 How Is the Cell Cycle Controlled? The Activities of Specific Enzymes Drive the Cell Cycle Checkpoints Control Progression Through the Cell Cycle

Enzymes Drive the Cell Cycle The cell cycle is driven by proteins called Cyclin-dependent kinases, or Cdk’s Kinases are enzymes that phosphorylate (add a phosphate group to) other proteins, stimulating or inhibiting their activity Cdk’s are active only when they bind to other proteins called cyclins

Enzymes Drive the Cell Cycle Cell division occurs when growth factors bind to cell surface receptors, which leads to cyclin synthesis Cyclins then bind to and activate specific Cdk’s

FIGURE 11-14 The G1 to S checkpoint Progress through the cell-cycle checkpoints is under the overall control of cyclin and cyclin-dependent kinases (Cdk's). In the G1 to S checkpoint illustrated here, growth factors stimulate synthesis of cyclin proteins, which activate Cdk's, starting a cascade of events that lead to DNA replication.

Checkpoints Control Cell Cycle Although Cdk’s drive the cell cycle, multiple checkpoints ensure that The cell successfully completes DNA synthesis during interphase Proper chromosome movements occur during mitotic cell division

Checkpoints Control Cell Cycle There are three major checkpoints in the eukaryotic cell cycle, each regulated by protein complexes G1 to S: G2 to mitosis Metaphase to anaphase

FIGURE 11-13 Control of the cell cycle Three major "checkpoints" regulate a cell's transitions from one phase of the cell cycle to the next: (1) G1 to S, (2) G2 to mitosis (M), and (3) metaphase to anaphase.

Checkpoints Control Cell Cycle G1 to S: Ensures that the cell’s DNA is suitable for replication p53 protein expressed when DNA is damaged Inhibits replication Stimulates synthesis of DNA repair enzymes Triggers cell death (apoptosis) if damage can’t be repaired

FIGURE 11-15 Controlling the transition from G1 to S (a) The Rb protein inhibits DNA synthesis. Toward the end of the G1 phase, cyclin levels rise. These activate Cdk, which then adds a phosphate group to the Rb protein. Phosphorylated Rb no longer inhibits DNA synthesis, so the cell enters the S phase. (b) Damaged DNA stimulates increased levels of the p53 protein, which triggers a cascade of events that inhibit Cdk, thereby preventing entry into the S phase until the DNA has been repaired.

11.6 Why Do So Many Organisms Reproduce Sexually? Mutations in DNA are the ultimate source of genetic variability Sexual reproduction may combine different parental alleles in a single offspring Creates lot of variation

Mutations are the raw material for evolution gene 1 gene 2 same alleles different alleles Figure: 11-UN4 Title: Alleles Mutations are the raw material for evolution

Section 11.6 Outline 11.6 How Does Meiotic Cell Division Produce Haploid Cells? Meiosis Separates Homologous Chromosomes to Produce Haploid Daughter Nuclei Fusion of Gametes Keeps Chromosome Number Constant Between Generations Events of Meiotic Prophase I Events of Meiotic Metaphase I

Section 11.6 Outline 11.6 How Does Meiotic Cell Division Produce Haploid Cells? (continued) Events of Meiotic Anaphase I and Telophase I Summary of Events of Meiosis II

sister chromatids homologous chromosomes Figure: 11-UN5 Title: Homologous chromosomes Both members of a pair of homologous chromosomes are replicated prior to meiosis Copyright © 2005 Pearson Prentice Hall, Inc.

During meiosis I, each daughter cell receives one member of each pair of homologous chromosomes Figure: 11-UN6 Title: Two daughter nuclei

During meiosis II, sister chromatids separate into independent chromosomes (1n) Figure: 11-UN7 Title: Four haploid cells

2n n meiotic cell division 2n 2n n fertilization Figure: 11-UN8 Title:

duplicated chromosomes sister chromatids of one duplicated homologue Figure: 11-12 part a Title: The mechanism of crossing over part a Duplicated homologous chromosomes pair up side by side. pair of homologous, duplicated chromosomes Duplicated homologous chromosomes pair up side by side. Copyright © 2005 Pearson Prentice Hall, Inc.

Protein strands “zip” the homologous chromosomes together. joining duplicated chromosomes direction of “zipper” formation Figure: 11-12 part b Title: The mechanism of crossing over part b Protein strands "zip" the homologous chromosomes together. Protein strands “zip” the homologous chromosomes together. Copyright © 2005 Pearson Prentice Hall, Inc.

Recombination enzymes bind to the joined chromosomes. Figure: 11-12 part c Title: The mechanism of crossing over part c Recombination enzymes bind to the joined chromosomes. Recombination enzymes bind to the joined chromosomes. Copyright © 2005 Pearson Prentice Hall, Inc.

Recombination enzymes snip chromatids apart and chiasma Recombination enzymes snip chromatids apart and reattach the free ends. Chiasmata (the sites of crossing over) form when one end of the paternal chromatid (yellow) attaches to the other end of a maternal chromatid (purple). Figure: 11-12 part d Title: The mechanism of crossing over part d Recombination enzymes snip chromatids apart and reattach the free ends. Chiasmata (the sites of crossing over) form when one end of the paternal chromatid (yellow) attaches to the other end of a maternal chromatid (purple). Copyright © 2005 Pearson Prentice Hall, Inc.

Genetic recombination Crossing over Genetic recombination Figure: 11-12 part e Title: The mechanism of crossing over part e Recombination enzymes and protein zippers leave. Chiasmata remain, helping to hold homologous chromosomes together. chiasma Recombination enzymes and protein zippers leave. Chiasmata remain, helping to hold homologous chromosomes together. Copyright © 2005 Pearson Prentice Hall, Inc.

FIGURE 11-21 (part 1) Meiotic cell division in an animal cell In meiotic cell division (meiosis and cytokinesis), the homologous chromosomes of a diploid cell are separated, producing four haploid daughter cells. Each daughter cell contains one member of each pair of parental homologous chromosomes. In these diagrams, two pairs of homologous chromosomes are shown, large and small. The yellow chromosomes are from one parent (for example, the father), and the violet chromosomes are from the other parent (for example, the mother).

FIGURE 11-21 (part 2) Meiotic cell division in an animal cell In meiotic cell division (meiosis and cytokinesis), the homologous chromosomes of a diploid cell are separated, producing four haploid daughter cells. Each daughter cell contains one member of each pair of parental homologous chromosomes. In these diagrams, two pairs of homologous chromosomes are shown, large and small. The yellow chromosomes are from one parent (for example, the father), and the violet chromosomes are from the other parent (for example, the mother).

Meiosis I Mitosis spindle duplicated microtubules chromosomes Figure: 11-UN9,10 Title: Mitosis, Meiosis I Meiosis I Mitosis

Table 11-1a A Comparison of Mitotic and Meiotic Cell Divisions in Animal Cells

Table 11-1b (part 2) A Comparison of Mitotic and Meiotic Cell Divisions in Animal Cells

Section 11.7 Outline 11.7 When Do Mitotic and Meiotic Cell Divisions Occur in the Life Cycles of Eukaryotes? In Haploid Life Cycles, the Majority of the Cycle Consists of Haploid Cells In Diploid Life Cycles, the Majority of the Cycle Consists of Diploid Cells In Alternation-of-Generation Life Cycles, There Are Both Diploid and Haploid Multicellular Stages

FIGURE 11-25 The three major types of eukaryotic life cycles The lengths of the arrows correspond roughly to the proportion of the life cycle spent in each stage.

FIGURE 11-26 The life cycle of the unicellular alga, Chlamydomonas Chlamydomonas reproduces asexually by mitotic cell division of haploid cells. When nutrients are scarce, specialized haploid cells (usually from genetically different populations) fuse to form a diploid cell. Meiotic cell division then immediately produces four haploid cells, usually with different genetic compositions than either of the parental strains.

FIGURE 11-27 The human life cycle Through meiotic cell division, the two sexes produce gametes—sperm in males and eggs in females—that fuse to form a diploid zygote. Mitotic cell division and differentiation of the daughter cells produce an embryo, child, and ultimately a sexually mature adult. The haploid stages last only a few hours to a few days; the diploid stages may survive for a century.

FIGURE 11-28 Alternation of generations in plants In plants, such as this fern, specialized cells in the multicellular diploid stage undergo meiotic cell division to produce haploid spores. The spores undergo mitotic cell division and differentiation of the daughter cells to produce a multicellular haploid stage. Sometime later, perhaps many weeks later, some of these haploid cells differentiate into sperm and eggs. These fuse to form a diploid zygote. Mitotic cell division and differentiation once again give rise to a multicellular diploid stage.

11.8 How Do Meiosis and Sexual Reproduction Produce Genetic Variability? Shuffling of homologues creates novel combinations of chromosomes Crossing over creates chromosomes with novel combinations of genes Fusion of gametes adds further genetic variability to the offspring

Independent Assortment Figure: 11-UN11 Title: Chromosome configurations at metaphase I There are 2 choices for each spot. 223 ≈ 8 million different gametes each human can make without even considering crossing over