12 cellcycle text

Cell Replication ,[object Object],Figure 12.1

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],100 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM). Figure 12.2 A 20 µm 200 µm (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). Figure 12.2 B, C

[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],0.5 µm Chromosome duplication (including DNA synthesis) Centromere Separation of sister chromatids Sister chromatids Centromeres Sister chromatids A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Figure 12.4

Phases of the Cell Cycle ,[object Object],[object Object],[object Object],INTERPHASE G 1 S (DNA synthesis) G 2 Cytokinesis Mitosis MITOTIC (M) PHASE Figure 12.5

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],G 2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Figure 12.6 Nonkinetochore microtubules

[object Object],[object Object],[object Object],Centrosome at one spindle pole Daughter chromosomes METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Figure 12.6

The Mitotic Spindle: A Closer Look ,[object Object],[object Object],[object Object],[object Object],Centrosome Aster Sister chromatids Metaphase Plate Kinetochores Overlapping nonkinetochore microtubules Kinetochores microtubules Centrosome Chromosomes Microtubules 0.5 µm 1 µm Figure 12.7

[object Object],[object Object],EXPERIMENT 1 The microtubules of a cell in early anaphase were labeled with a fluorescent dye that glows in the microscope (yellow). Spindle pole Kinetochore Figure 12.8

[object Object],[object Object],[object Object],[object Object]

Cytokinesis: A Closer Look ,[object Object],[object Object],Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm (a) Cleavage of an animal cell (SEM) Figure 12.9 A

[object Object],[object Object],Daughter cells 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (b) Cell plate formation in a plant cell (SEM) Figure 12.9 B

[object Object],1 Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from. Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelop will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their kinetochore microtubles shorten. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell. 2 3 4 5 Nucleus Nucleolus Chromosome Chromatine condensing Figure 12.10

Binary Fission ,[object Object],[object Object],Origin of replication E. coli cell Bacterial Chromosome Cell wall Plasma Membrane Two copies of origin Origin Origin Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. 1 Replication continues. One copy of the origin is now at each end of the cell. 2 Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. 3

The Cell Cycle Control System ,[object Object],[object Object],Figure 12.14 Control system G 2 checkpoint M checkpoint G 1 checkpoint G 1 S G 2 M

[object Object],[object Object],G 1 checkpoint G 1 G 1 G 0 (a) If a cell receives a go-ahead signal at the G 1 checkpoint, the cell continues on in the cell cycle. (b) If a cell does not receive a go-ahead signal at the G 1 checkpoint, the cell exits the cell cycle and goes into G 0 , a nondividing state. Figure 12.15 A, B

The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases ,[object Object],[object Object]

[object Object],[object Object],During G 1 , conditions in the cell favor degradation of cyclin, and the Cdk component of MPF is recycled. 5 During anaphase, the cyclin component of MPF is degraded, terminating the M phase. The cell enters the G 1 phase. 4 Accumulated cyclin molecules combine with recycled Cdk molecules, producing enough molecules of MPF to pass the G 2 checkpoint and initiate the events of mitosis. 2 Synthesis of cyclin begins in late S phase and continues through G 2 . Because cyclin is protected from degradation during this stage, it accumulates. 1 Cdk Cdk G 2 checkpoint Cyclin MPF Cyclin is degraded Degraded Cyclin G 1 G 2 S M G 1 G 1 S G 2 G 2 S M M MPF activity Cyclin Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle (b) Molecular mechanisms that help regulate the cell cycle MPF promotes mitosis by phosphorylating various proteins. MPF‘s activity peaks during metaphase. 3 Figure 12.16 A, B M

Stop and Go Signs: Internal and External Signals at the Checkpoints ,[object Object],[object Object]

[object Object],[object Object],25 µm Cancer cells do not exhibit anchorage dependence or density-dependent inhibition. Cancer cells. Cancer cells usually continue to divide well beyond a single layer, forming a clump of overlapping cells. (b) Figure 12.18 B

Loss of Cell Cycle Controls in Cancer Cells ,[object Object],[object Object],[object Object]

[object Object],[object Object],Figure 12.19 Cancer cells invade neighboring tissue. 2 A small percentage of cancer cells may survive and establish a new tumor in another part of the body. 4 Cancer cells spread through lymph and blood vessels to other parts of the body. 3 A tumor grows from a single cancer cell. 1 Tumor Glandular tissue Cancer cell Blood vessel Lymph vessel Metastatic Tumor

Meiosis ,[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Figure 13.1

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Comparison of Asexual and Sexual Reproduction ,[object Object],[object Object],Figure 13.2 Parent Bud 0.5 mm

Sets of Chromosomes in Human Cells ,[object Object],[object Object],[object Object]

[object Object],[object Object],5 µ m Pair of homologous chromosomes Centromere Sister chromatids Figure 13.3

[object Object],[object Object],Key Maternal set of chromosomes ( n = 3) Paternal set of chromosomes ( n = 3) 2 n = 6 Two sister chromatids of one replicated chromosome Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set) Centromere Figure 13.4

[object Object],Figure 13.5 Key Haploid ( n ) Diploid (2 n ) Haploid gametes ( n = 23) Ovum ( n ) Sperm Cell (n) MEIOSIS FERTILIZATION Ovary Testis Diploid zygote (2 n = 46) Mitosis and development Multicellular diploid adults (2 n = 46)

[object Object],[object Object],[object Object],Gametes Figure 13.6 A Diploid multicellular organism Key MEIOSIS FERTILIZATION n n n 2n 2n Zygote Haploid Diploid Mitosis (a) Animals

[object Object],[object Object],[object Object],MEIOSIS FERTILIZATION n n n n n 2n 2n Haploid multicellular organism (gametophyte) Mitosis Mitosis Spores Gametes Mitosis Zygote Diploid multicellular organism (sporophyte) (b) Plants and some algae Figure 13.6 B

[object Object],[object Object],[object Object],MEIOSIS FERTILIZATION n n n n n 2n Haploid multicellular organism Mitosis Mitosis Gametes Zygote (c) Most fungi and some protists Figure 13.6 C

[object Object],[object Object],[object Object]

The Stages of Meiosis ,[object Object],Figure 13.7 Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes 1 2 Homologous chromosomes separate Haploid cells with replicated chromosomes Sister chromatids separate Haploid cells with unreplicated chromosomes Meiosis I Meiosis II

[object Object],Figure 13.8 Centrosomes (with centriole pairs) Sister chromatids Chiasmata Spindle Tetrad Nuclear envelope Chromatin Centromere (with kinetochore) Microtubule attached to kinetochore Tertads line up Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Pairs of homologous chromosomes split up Chromosomes duplicate Homologous chromosomes (red and blue) pair and exchange segments; 2 n = 6 in this example INTERPHASE MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I

[object Object],TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS MEIOSIS II: Separates sister chromatids Cleavage furrow Sister chromatids separate Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes Two haploid cells form; chromosomes are still double Figure 13.8

A Comparison of Mitosis and Meiosis ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 13.9 MITOSIS MEIOSIS Prophase Duplicated chromosome (two sister chromatids) Chromosome replication Chromosome replication Parent cell (before chromosome replication) Chiasma (site of crossing over) MEIOSIS I Prophase I Tetrad formed by synapsis of homologous chromosomes Metaphase Chromosomes positioned at the metaphase plate Tetrads positioned at the metaphase plate Metaphase I Anaphase I Telophase I Haploid n = 3 MEIOSIS II Daughter cells of meiosis I Homologues separate during anaphase I; sister chromatids remain together Daughter cells of meiosis II n n n n Sister chromatids separate during anaphase II Anaphase Telophase Sister chromatids separate during anaphase 2 n 2 n Daughter cells of mitosis 2 n = 6

Independent Assortment of Chromosomes ,[object Object],[object Object]

[object Object],[object Object],Figure 13.10 Key Maternal set of chromosomes Paternal set of chromosomes Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Possibility 2 Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4

Crossing Over ,[object Object],[object Object], Variation Figure 13.11 Prophase I of meiosis Nonsister chromatids Tetrad Chiasma, site of crossing over Metaphase I Metaphase II Daughter cells Recombinant chromosomes

Random Fertilization ,[object Object],[object Object],Number of children from one couple without two exactly the same: 10 2017

Wild dogs 1 Aardwolf African wild dog Arctic fox Argentine gray fox Black-backed jackal Blanford’s fox Bat-eared fox Bush dog Wild dogs

Wild dogs 2 Wild dogs Arctic wolf Cape fox Corsac fox Coyote Crab-eating fox Culpeo fox Dhole Fennec fox

Wild dogs Arctic fox Dingo Dingo Ethiopian wolf Falkland Island’s fox Golden jackal Tibetan sand fox Gray wolf

Wild dogs 4 Wild dogs Gray fox Hoary zorro Kit fox Maned wolf Mexican gray wolf Raccoon dog Sand fox Small-eared dog

Wild dogs 5 Wild dogs Pale fox Pampas fox Red fox Red wolf Sechuan zorro Timber wolf Iberian wolf

Q 910 Savolainen, et.al The origin of the domestic dog from wolves has been established … we examined the mitochondrial DNA (mtDNA) sequence variation among 654 domestic dogs representing all major dog populations worldwide … suggesting a common origin from a single gene pool for all dog populations . Q 910 Savolainen, et.al., ‘Genetic Evidence for an East Asian origin of Domestic Dogs,’ Science , Vol 298:5598, 22 Nov 2002, pp 1610-1613.

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