BIOLOGY: Today and Tomorrow, 4e starr evers starr Chapter 8 How Cells Reproduce

8.1 Henrietta’s Immortal Cells  Henrietta Lacks died of cervical cancer more than 50 years ago, but her cells live on in research laboratories  HeLa cells are widely used to investigate cancer, viral growth, protein synthesis, effects of radiation, and many other processes important in medicine and research  Understanding why cancer cells are immortal – and we are not – begins with understanding the structures and mechanisms that cells use to divide

Dividing HeLa Cells

8.2 Multiplication by Division  A cell reproduces by dividing in two  Each descendant cell receives a full set of chromosomes and some cytoplasm  Before the cell’s cytoplasm divides, it must first replicate its chromosomes  Duplicated chromosomes are separated and packaged into new nuclei by one of two mechanisms: mitosis or meiosis

Mitosis and Meiosis  Mitosis is a nuclear division mechanism that maintains the chromosome – used in growth, development, replacement of damaged or dead cells, or as part of asexual reproduction  Meiosis is a nuclear division mechanism that halves the chromosome number – used in sexual reproduction, in which two parents contribute genes to offspring

Divisions of a Fertilized Frog Egg

Cellular Division Mechanisms

8.3 Mitosis and the Cell Cycle  Cell cycle  A series of events from the time a cell forms until its cytoplasm divides  Includes three phases: interphase, mitosis, and cytoplasmic division

Interphase  Most of a cell’s activities occur in interphase  Interphase  In a eukaryotic cell cycle, the interval between mitotic divisions when a cell grows, roughly doubles the number of its cytoplasmic components, and replicates its DNA  Three stages:  G1, 1 st interval (gap) of growth before DNA replication  S, interval of synthesis (DNA replication)  G2, 2 nd interval (gap) when the cell prepares to divide

The eukaryotic cell cycle

Controls Over the Cell Cycle  When a cell divides—and when it does not—is determined by gene expression controls  Products of “checkpoint genes” monitor whether a cell’s DNA has been copied completely, whether it is damaged, and whether enough nutrients are available  If a problem remains uncorrected, other checkpoint proteins may cause the cell to self-destruct

Homologous Chromosomes  Human body cells have 23 chromosome pairs  Except for a pairing of sex chromosomes (XY) in males, the chromosomes of each pair are homologous  Homologous chromosomes are members of a pair of chromosomes with the same length, shape, and genes  One member of a homologous pair was inherited from the female parent, and the other from the male parent

How Mitosis Maintains Chromosome Number  Mitosis distributes a complete set of chromosomes into two new nuclei  In G2, each chromosomes consists of two replicated DNA molecules attached at the centromere (sister chromatids)  When sister chromatids are pulled apart, each becomes an individual chromosome in a new nucleus  When the cytoplasm divides, the two nuclei are packaged into two separate cells

How 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 cytoplasmic division package one copy of each chromosome into each of two new cells.

Figure 8-4 p135 A) An unduplicated pair of chromosomes in a cell in G1. Stepped Art B) By G2, each chromosome has been duplicated. C) Mitosis and cytoplasmic division package one copy of each chromosome into each of two new cells.

The Process of Mitosis  Prophase  Chromosomes condense and spindle forms  Nuclear envelope breaks up  Spindle microtubules attach to chromosomes  Spindle  Moves chromosomes during nuclear division  Dynamically assembled and disassembled microtubules

The Process of Mitosis  Metaphase  Duplicated homologous chromosomes line up at the spindle equator (halfway between spindle poles)  Sister chromatids begin to move apart toward opposite spindle poles  Anaphase  Microtubules separate sister chromatids of each chromosome and pull them toward opposite spindle poles  Each DNA molecule is now a separate chromosome

The Process of Mitosis  Telophase  Two clusters of chromosomes arrive at the spindle poles and decondense; new nuclei form  End of mitosis  Nuclear envelopes form around the two clusters of chromosomes, forming two new nuclei with the parental chromosome number

Mitosis in a plant cellMitosis in an animal cell pair of centrioles 1 1 Interphase Interphase cells are shown for comparison, but interphase is not part of mitosis. The red spots in the plant cell nucleus are areas where ribosome subunits are being transcribed and assembled. Mitosis

Mitosis in a plant cellMitosis in an animal cell 2 2 Early prophase Mitosis begins. Transcription stops, and the DNA begins to appear grainy as it starts to condense. The centriole pair gets duplicated. Mitosis

Mitosis in a plant cellMitosis in an animal cell microtubule of spindle 3 3 Prophase The duplicated chromosomes become visible as they condense. One of the two centriole pairs moves to the opposite side of the cell. The nuclear envelope breaks up. Spindle microtubules assemble and bind to chromosomes at the centromere. Sister chromatids become attached to opposite centriole pairs. Mitosis

Mitosis in a plant cellMitosis in an animal cell 4 4 Metaphase All of the chromosomes are aligned in the middle of the cell. Mitosis

Mitosis in a plant cellMitosis in an animal cell 5 5 Anaphase Spindle microtubules separate the sister chromatids and move them toward opposite sides of the cell. Each sister chromatid has now become an individual, unduplicated chromosome. Mitosis

Mitosis in a plant cellMitosis in an animal cell 6 6 Telophase The chromosomes reach opposite sides of the cell and decondense. Mitosis ends when a new nuclear envelope forms around each cluster of chromosomes. Mitosis

ANIMATED FIGURE: Random alignment 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 HERECLICK HERE

ANIMATED FIGURE: 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 HERECLICK HERE

3D ANIMATION: Mitosis

8.4 Cytoplasmic Division Mechanisms  A cell’s cytoplasm divides between late anaphase and the end of telophase, forming two cells, each with its own nucleus  Mechanisms of cytoplasmic division differ between animal cells and plant cells

Cytoplasmic Division in Animal Cells  In animal cells, a contractile ring pinches the cytoplasm in two  A contractile ring of microfilaments contracts when its component proteins are energized by ATP  The cleavage furrow produced deepens until the cytoplasm (and the cell) is pinched in two  Each new cell has its own nucleus, cytoplasm, and is enclosed by a plasma membrane

Cytoplasmic Division of an Animal Cell

Cytoplasmic Division in Plant Cells  In plant cells, microtubules guide vesicles from Golgi bodies and the cell surface to the division plane  Vesicles and their wall-building contents fuse into a disk- shaped cell plate  The cell plate grows and forms a cross-wall between the two new nuclei  The cell plate develops into two new cell walls, separating the descendant cells

Cytoplasmic Division of a Plant Cell

ANIMATED FIGURE: Cytoplasmic division 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 HERECLICK HERE

8.5 When Mitosis Becomes Pathological  When checkpoint mechanisms fail, the cell may skip interphase and keep dividing with no resting period  Signaling mechanisms that make an abnormal cell die may stop working  Mutations are passed along to the cell’s descendants, which form a neoplasm, an accumulation of cells that lost control over how they grow and divide

Tumors and Oncogenes  A neoplasm that forms a lump is a tumor  An oncogene is any gene that helps transform a normal cell into a tumor cell  Genes for proteins that promote mitosis are called proto- oncogenes because mutations can turn them into oncogenes  Example: Genes that code for receptors for growth factors

An oncogene causing a neoplasm

Tumor Suppressors  Checkpoint gene products that inhibit mitosis are called tumor suppressors because tumors form when they are missing  Example: Products of BRCA1 and BRCA2 genes  Viruses such as HPV cause a cell to make proteins that interfere with its own tumor suppressors

Checkpoint genes control cell division

Cancer  A benign neoplasm such as a mole is noncancerous; a malignant neoplasm is dangerous to health  Cancer occurs when abnormally dividing cells of a malignant neoplasm disrupt body tissues, physically and metabolically  Malignant neoplasms can break free and invade other tissues (metastasis)

Metastasis Benign neoplasms grow slowly and stay in their home tissue. Cells of a malignant neoplasm can break away from their home tissue. Malignant cells can become attached to the wall of a blood vessel or lymph vessel. They release enzymes that create an opening in the wall, then enter the vessel. The cells creep or tumble along in blood vessels, then leave the bloodstream the same way they got in. They may start growing in other tissues, a process called metastasis

Three Characteristics of Cancer Cells 1. Grow and divide abnormally 2. Abnormal plasma membrane, cytoskeleton, chromosome number, and metabolism 3. Cells do not stay anchored properly in tissues because plasma membrane adhesion proteins are defective or missing

Detecting Skin Cancer C) Melanoma, a malignant neoplasm of skin cells, spreads fastest. Cells form dark, encrusted lumps that may itch or bleed easily. B) The second most common form of skin cancer is a squamous cell carcinoma. This pink growth, firm to the touch, grows under the surface of skin. A) Basal cell carcinoma is the most common type of skin cancer. This slow growing, raised lump may be uncolored, reddish brown, or black.

ANIMATED FIGURE: Cancer and metastasis 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 HERECLICK HERE

VIDEO: Genome Research Improving Cancer Understanding

VIDEO: The War on Cancer

VIDEO: Genetically Modified Virus Used to Fight Cancer

8.6 Sex and Alleles  Asexual reproduction  Offspring arise from one parent  Offspring are genetic clones  Sexual reproduction  Offspring inherit genes from two parents  Diversity offers a better chance of surviving an environmental challenge or harmful mutations  Beneficial mutations spread quickly

Introducing Alleles  Paired genes on homologous chromosomes often vary slightly in DNA sequence  Alleles are forms of a gene that encode slightly different versions of the gene’s product  Offspring of sexual reproducers inherit new combinations of alleles, which is the basis of new combinations of traits

A) Corresponding colored patches in this fluorescence micrograph indicate corresponding DNA sequences in a homologous chromosome pair. These chromosomes carry the same set of genes. Alleles

Genes occur in pairs on homologous chromosomes. The members of each pair of genes may be identical, or they may differ slightly, as alleles. B) Homologous chromosomes carry the same series of genes, but the DNA sequence of any one of those genes might differ just a bit from that of its partner on the homologous chromosome. Alleles

ANIMATED FIGURE: Genetic terms 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 HERECLICK HERE

8.7 Meiosis and the Life Cycle  Meiosis halves the parental chromosome number by sorting the chromosomes into new nuclei twice (meiosis I and meiosis II)  Duplicated chromosomes of a diploid nucleus (2n) are distributed into four haploid nuclei (n)

Two Stages of Meiosis

Meiosis  Meiosis I  In the first nuclear division, duplicated homologous chromosomes line up and cross over, then move apart, toward opposite spindle poles  Two new nuclear envelopes form around the two clusters of still-duplicated chromosomes  Meiosis II  The second nuclear division separates sister chromatids  Four haploid nuclei typically form, each with one complete set of unduplicated chromosomes

Meiosis IOne diploid nucleus to two haploid nuclei Prophase IMetaphase IAnaphase ITelophase I plasma membrane spindle nuclear envelope breaking up centiole pair one pair of homologous chromosomes Meiosis

No DNA replication Meiosis II Two haploid nuclei to four haploid nuclei Prophase IIMetaphase IIAnaphase IITelophase II Meiosis

Meiosis Mixes Alleles  Meiosis shuffles parental combinations of alleles, introducing variation in offspring  Crossing over in prophase I  Random assortment in metaphase I  Crossing over is recombination between nonsister chromatids of homologous chromosomes which produces new combinations of parental alleles

A) Here, we focus on only two of the many genes on a chromosome. In this example, one gene has alleles A and a; the other has alleles B and b. Crossing Over

crossover B) Close contact between homologous chromosomes promotes crossing over between nonsister chromatids, which exchange corresponding pieces. Crossing Over

C) Crossing over mixes up paternal and maternal alleles on homologous chromosomes. Crossing Over

From Gametes to Offspring  Sexual reproduction involves the fusion of reproductive cells (gametes) from two parents  All gametes are haploid, and they arise by division of immature reproductive cells (germ cells)  At fertilization, two haploid gametes fuse and produce a diploid zygote, which is the first cell of a new individual

Gametes in Animals and Plants  In animals, meiosis of germ cells in the reproductive organs give rise to sperm (male gametes) or eggs (female gametes)  In plants, two kinds of multicelled bodies form:  A diploid sporophyte produces spores by meiosis  Gametes form in a haploid gametophyte

mitosis zygote (2n) multicelled body (2n) Diploid Fertilization Haploid Meiosis gametes (n) A) Generalized life cycle for most animals. Generalized life cycle for animals

mitosis zygote (2n) multicelled sporophyte (2n) Diploid Fertilization Haploid Meiosis gametes (n) spores (n) multicelled gametophyte (n) B) Generalized life cycle for most plants. Generalized life cycle for plants

ANIMATED FIGURE: Crossing over 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 HERECLICK HERE

ANIMATED FIGURE: Generalized life cycles 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 HERECLICK HERE

ANIMATION: Meiosis I and II 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 HERECLICK HERE

3D ANIMATION: Meiosis

ANIMATION: Crossover review 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 HERECLICK HERE

ANIMATION: Stages of Mitosis and Meiosis 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 HERECLICK HERE

ANIMATION: Meiosis and Mitosis Drag and Drop 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 HERECLICK HERE

8.8 Henrietta’s Immortal Cells (revisited)  HeLa cells were used in early tests of taxol, a drug that keeps microtubules from disassembling and interferes with mitosis  The HeLa cell line was established more than 50 years ago without Henrietta Lacks knowledge or consent  Today, consent forms are required to take tissue samples

Digging Into Data: HeLa Cells Are a Genetic Mess