Cell Division and Reproduction PDF

Cell Division and Reproduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell Division Ensures the Passage of Genetic Information 8-2 Fig. 12-2 Functions of Cell Division 100...

Cell Division and Reproduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cell Division Ensures the Passage of Genetic Information 8-2 Fig. 12-2 Functions of Cell Division 100 µm 200 µm 20 µm (a) Reproduction (b) Growth and (c) Tissue renewal development  Cell division is involved in both asexual and sexual reproduction § Somatic cells - body cells make up most of the organism § Asexual reproduction - increase in number of somatic cells or the number of unicellular organisms § Germ cells - found only in testes and ovaries, they produce sperm or eggs § Sexual reproduction – requires the production of eggs and sperm 8-4 Prokaryotes reproduce asexually § In bacteria and archaea, reproduction consists of duplicating the single chromosome, located in the nucleoid, and distributing a copy to each daughter cell 8-5 Figure 8.2 Prokaryotes use binary fission to reproduce 8-6 Somatic Cells Have a Cell Cycle and Undergo Mitosis and Cytokinesis 8-7  Eukaryotic cell cycle is a set series of events § Interphase - the time when a cell performs its usual functions Figure 8.3A Stages of the cell cycle. 8-8  M (Mitotic) Stage § Cell division occurs during the M stage and encompasses both division of the nucleus and division of the cytoplasm § Mitosis - nuclear division in the cell cycle § Cytokinesis - division of the cytoplasm 8-9 Figure 8.3B Cytokinesis is a noticeable part of the cell cycle 8-10  Eukaryotic chromosomes are visible during cell division § When a eukaryotic cell is not undergoing division, the DNA within a chromosome is a mass of thin threads called chromatin § Before nuclear division chromatin condenses, § 2 identical chromatids are sister chromatids 8-11 Figure 8.4A A condensed duplicated chromosome 8-12  duplicated chromosome chromatin  Somatic Cells Are Diploid (2n) § Diploid (2n) - includes two chromosomes of each kind § During mitosis, a 2n nucleus divides to produce daughter nuclei that are also 2n § A dividing cell is called the parent cell and the new cells are called the daughter cells 8-14  Gametes Are Haploid (n) § Haploid (n) number of chromosomes, contains only one chromosome of each kind § Half the diploid number Figure 8.4B When sister chromatids separate, each daughter 8-15 nucleus gets a chromosome  Mitosis maintains the chromosome number § Before mitosis, DNA has replicated, each double helix is in a chromatid and the chromosomes consist of sister chromatids attached at a centromere § The centrosome - the microtubule-organizing center of the cell divides before mitosis § Spindle fibers separate the sister chromatids of the duplicated chromosomes 8-16 Fig. 12-6a G2 of Interphase Prophase Prometaphase Fig. 12-6b G2 of Interphase Prophase Prometaphase Centrosomes Chromatin Early mitotic Aster Centromere Fragments Nonkinetochore (with centriole (duplicated) spindle of nuclear microtubules pairs) envelope Nucleolus Nuclear Plasma Chromosome, consisting Kinetochore Kinetochore envelope membrane of two sister chromatids microtubule Fig. 12-6c Metaphase Anaphase Telophase and Cytokinesis Fig. 12-6d Metaphase Anaphase Telophase and Cytokinesis Metaphase Cleavage Nucleolus plate furrow forming Daughter Nuclear Spindle Centrosome at chromosomes one spindle pole envelope forming Fig. 12-9 Vesicles Wall of 1 µm 100 µm forming parent cell Cleavage furrow cell plate Cell plate New cell wall Contractile ring of Daughter cells microfilaments Daughter cells (a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM) Figure 8.6A Cytokinesis in an animal cell 8-22 Figure 8.6B Cytokinesis in plant cells 8-23 Fig. 12-10 Nucleus Chromatin 10 µm Nucleolus condensing Chromosomes Cell plate 1 Prophase 2 Prometaphase 3 Metaphase 4 Anaphase 5 Telophase Fig. 12-10a Nucleus Chromatin Nucleolus condensing 1 Prophase Fig. 12-10b Chromosomes 2 Prometaphase Fig. 12-10c 3 Metaphase Fig. 12-10d 4 Anaphase Fig. 12-10e 10 µm Cell plate 5 Telophase Figure 8.5 Phases of mitosis in animal cells and plant cells 8-30 Figure 8.5 Phases of mitosis in animal cells and plant cells 8-31  Cytokinesis divides the cytoplasm § Cytokinesis follows mitosis in most cells § Cytokinesis in plant cells occurs by a process different than in animal cells § Cell plate - newly formed plasma membrane that expands outward 8-32 Cancer Is Uncontrolled Cell Division 8-33  Cell cycle control occurs at checkpoints § The cell cycle has checkpoints that can delay the cell cycle until all is well § Apoptosis - programmed cell death 8-34 Figure 8.7 Cell cycle checkpoints 8-35 Figure 8.9 Development of breast cancer 8-36 Fig. 12-20 Lymph vessel Tumor Blood vessel Cancer Glandular cell tissue Metastatic tumor 1 A tumor grows 2 Cancer cells 3 Cancer cells spread 4 Cancer cells may from a single invade neigh- to other parts of survive and cancer cell. boring tissue. the body. establish a new tumor in another part of the body.  Cell Cycle Inhibition § Contact Inhibition - In a culture, cells divide until they line a container in a sheet and then stop dividing § Cells “remember” number of divisions § Telomere - repeating DNA base sequence § Each time a cell divides some portion of a telomere is lost § When telomeres become too short, chromosomes fuse and do not duplicate 8-38  Cancer cells have abnormal characteristics § A mutation (a DNA change) causes a cell to divide uncontrollably or ignore apoptosis § Carcinogenesis - development of cancer § Characteristics of cancer cells § Lack differentiation § Have abnormal nuclei § Form tumors § Metastasis - establishing new tumors § Angiogenesis - formation of new blood vessels 8-39 DOWN SYNDROME AND MATERNAL AGE  APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES Protective behaviors and diet help prevent cancer § Behaviors that help prevent cancer § Don’t smoke § Use sunscreen § Avoid radiation § Be tested for cancer § Be aware of occupational hazards § Carefully consider hormone therapy § Dietary guidelines to reduce cancer risk § Increase consumption of foods rich in vitamins A and C § Limit consumption of salt-cured, smoked, or nitrite-cured foods § Include vegetables from the cabbage family § Be moderate in the consumption of alcohol § Maintain a healthy weight 8-42  Meiosis Produces Cells That Become the Gametes in Animals and Spores in Other Organisms 8-43  Homologous chromosomes separate during meiosis § Karyotype - picture of chromosomes in numbered pairs called homologous chromosomes or homologues § X and Y chromosomes are the sex chromosomes because they contain the genes that determine gender § Autosomes - all the pairs of chromosomes except the sex chromosomes 8-44 Figure 8.11 A karyotype shows that the chromosomes occur as pairs 8-45  Meiosis § Occurs during the production of the sperm and egg § Requires two divisions § Meiosis I - the chromosomes of each homologous pair separate § Meiosis II - the sister chromatids of each duplicated chromosome separate 8-46 8-47  Synapsis and crossing-over occur during meiosis I § Synapsis - homologous chromosomes come together and line up side by side forming a tetrad § Crossing-over - during synapsis, nonsister chromatids exchange genetic material 8-48 Figure 8.12A Synapsis of homologues 8-49 Figure 8.12B Crossing-over of nonsister chromatids 8-50  Sexual reproduction increases genetic variation § Fertilization, the union of a male and a female gamete, enhances genetic variation § Sexual reproduction brings about genetic variation, and some offspring may have a better chance of survival and reproductive success than others 8-51 Figure 8.13 Independent assortment increases genetic variation 8-52 Recombination Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © American Images, Inc/Getty Images 53  Meiosis requires two division cycles § Prophase, metaphase, anaphase, and telophase occur during both meiosis I and meiosis II § No replication of DNA occurs during a period called interkinesis between meiosis I and II 8-54 Figure 8.14A Phases of meiosis I 8-55 Figure 8.14A Phases of meiosis I 8-56 Figure 8.14B Phases of meiosis II 8-57 Figure 8.14B Phases of meiosis II 8-58 Fig. 13-8a Telophase I and Prophase I Metaphase I Anaphase I Cytokinesis Centrosome (with centriole pair) Sister chromatids remain attached Centromere Sister Chiasmata (with kinetochore) chromatids Spindle Metaphase plate Homologous Homologous Cleavage chromosomes chromosomes furrow separate Fragments Microtubule of nuclear attached to envelope kinetochore Fig. 13-8d Telophase II and Prophase II Metaphase II Anaphase II Cytokinesis Sister chromatids Haploid daughter cells separate forming Fig. 13-8 Telophase I and Telophase II and Prophase I Metaphase I Anaphase I Prophase II Metaphase II Anaphase II Cytokinesis Cytokinesis Centrosome (with centriole pair) Sister chromatids remain attached Centromere Sister Chiasmata (with kinetochore) chromatids Spindle Metaphase plate Sister chromatids separate Haploid daughter cells Homologous Cleavage forming Homologous chromosomes chromosomes furrow separate Fragments Microtubule of nuclear attached to envelope kinetochore The life cycle of most multicellular organisms includes both mitosis and meiosis § Life cycle - in sexually reproducing organisms, all the reproductive events from one generation to the next § Spermatogenesis in males, occurs in the testes and produces sperm § Oogenesis in females, occurs in the ovaries and produces eggs § Zygote - product of the sperm and egg joining during fertilization, has homologous pairs of chromosomes 8-62 Figure 8.15A Life cycle of humans 8-63 Figure 8.15B Life cycle of plants Figure 8.15C Life cycle of algae 8-64 Meiosis can be compared to mitosis 8-65 Chromosomal Abnormalities Can Be Inherited 8-66 An abnormal chromosome number is sometimes traceable to nondisjunction § Polyploidy - a eukaryote has three or more complete sets of chromosomes § Aneuploidy - an organism has more or less than the normal number of chromosomes § Monosomy only one of a type of chromosome § Trisomy three of a type of chromosome § Nondisjunction - in meiosis I homologues do not separate and both go into the same daughter cell, or in meiosis II sister chromatids fail to separate and both daughter chromosomes go to the same gamete 8-67 Figure 8.17A Nondisjunction of chromosomes during meiosis I of oogenesis, followed by fertilization with normal sperm 8-68 Figure 8.17B Nondisjunction of chromosomes during meiosis II of oogenesis, followed by fertilization with normal sperm 8-69  Abnormal chromosome numbers cause syndromes § Trisomy 21 (Down Syndrome) § Over 90% of individuals with Down syndrome have three copies of chromosome 21 § Abnormal Sex Chromosome Inheritance § Turner syndrome females are born with only a single X chromosome § A male with Klinefelter syndrome has two or more X chromosomes in addition to a Y chromosome 8-70  Trisomy 21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. extra chromosome 21 a. b. a: © Jose Carrilo/PhotoEdit; b: © CNRI/SPL/Photo Researchers 71  Changes in Sex Chromosome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Turner syndrome b. Klinefelter syndrome a: Courtesy UNC Medical Illustration and Photography; b: Courtesy Stefan D. Schwarz, http://klinefeltersyndrome.org 72  Abnormal chromosome structure also causes syndromes § Various agents in the environment, such as radiation, certain organic chemicals, or viruses, can cause chromosomes to break § Deletion - an end of a chromosome breaks off or two simultaneous breaks lead to the loss of an internal segment § Duplication - the presence of a particular chromosome segment more than once in the same chromosome § Inversion - a segment of a chromosome is turned 180 degrees § Translocation - the movement of a chromosome segment from one chromosome to another nonhomologous chromosome 8-73 Figure 8.19 Types of chromosomal mutations 8-74  Connecting the Concepts: § All cells receive DNA from preexisting cells through the process of cell division § Mitosis is part of the cell cycle, and there are negative consequences if the cell cycle comes out of synchronization § Meiosis is part of the production of gametes, which have half the number of chromosomes as the parent cell § Sexual reproduction increases genetic variability 8-75  A Comparison of Mitosis and Meiosis Mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell Meiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell The mechanism for separating sister chromatids is virtually identical in meiosis II and mitosis Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 13-9 MITOSIS MEIOSIS Chiasma MEIOSIS I Parent cell Chromosome Chromosome Prophase replication replication Prophase I Homologous chromosome Replicated chromosome 2n = 6 pair Metaphase Metaphase I Anaphase Anaphase I Telophase Telophase I Haploid n=3 Daughter cells of meiosis I 2n 2n MEIOSIS II Daughter cells n n n n of mitosis Daughter cells of meiosis II SUMMARY Property Mitosis Meiosis DNA Occurs during interphase before Occurs during interphase before meiosis I begins replication mitosis begins Number of One, including prophase, metaphase, Two, each including prophase, metaphase, anaphase, and divisions anahase, and telophase telophase Synapsis of Does not occur Occurs during prophase I along with crossing over homologous between nonsister chromatids; resulting chiasmata chromosomes hold pairs together due to sister chromatid cohesion Number of Two, each diploid (2n) and genetically Four, each haploid (n), containing half as many chromosomes daughter cells identical to the parent cell as the parent cell; genetically different from the parent and genetic cell and from each other composition Role in the Enables multicellular adult to arise from Produces gametes; reduces number of chromosomes by half animal body zygote; produces cells for growth, repair, and introduces genetic variability amoung the gametes and, in some species, asexual reproduction  Meiosis vs. Mitosis § Meiosis § Mitosis § Requires two nuclear § Requires one nuclear divisions division § Chromosomes synapse and § Chromosomes do not cross over synapse nor cross over § Centromeres survive § Centromeres dissolve in Anaphase I mitotic anaphase § Halves chromosome § Preserves chromosome number number § Produces four daughter § Produces two daughter nuclei nuclei § Produces daughter cells § Produces daughter cells genetically different from genetically identical to parent and each other parent and to each other § Used only for sexual § Used for asexual reproduction reproduction and growth 78 Thank you !!! Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.