Cellular Reproduction: Cells from Cells

Transcription

1 1 Chapter 8 Cellular Reproduction: Cells from Cells PowerPoint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko Unit overview Chapter 8 Cellular reproduction: mitosis & meiosis Cell cycle How cells divide Mitosis cell division producing identical cells Meiosis cell division producing gametes Chapter 9 Patterns of inheritance: Genetics Mendelian Genetics How inherited genes determine traits the simple way Variations to Mendel s Laws The more complex ways genes determine traits. Chapter 10 The structure and function of DNA Replication, transcription and translation flow of genetic information and going from DNA to protein 2 From molecules to traits: a brief overview Genes Segments of DNA that encode a polypeptide (or other functional product) Flow of genetic information DNA DNA = Replication DNA RNA = Transcription ( same language ) RNA protein = Translation ( convert between languages ) How protein are born A gene which is a segment of DNA in within the nucleus is transcribed into mrna which leaves nucleus and is translated into a polypeptide by ribosomes in the cytosol (and either attached or unattached to ER) How proteins determine traits Traits (whether physical or functional) are determined by the metabolic processes of proteins Hair color is determined by the enzymes that produce various pigments Different people have different genetic sequences which produce different enzymes for hair color Pearson Education, Inc. Other proteins regulate which genes are expressed 3 Figure 11.UN06 DNA unpacking Transcription RNA processing RNA transport mrna breakdown Translation Protein activation Protein breakdown 4

2 From cells to humans: a brief overview 5 Figure 17.2 Sperm 6 2 FERTILIZATION Gametogenesis From somatic (body) cells to gametes (how sperm and eggs are formed) Fertilization When gametes join to form a zygote which is a single cell capable of developing into an independent organism. Cell division - A zygote divides symmetrically into a multicellular embryo initially with identical cells Cell differentiation - Cells divide asymmetrically and/or differentiate due to cell-cell signaling to give different cell types that become different tissues Further differentiation, growth and development Cells continue to differentiate and become specialized to give functional tissues, organs, and organ systems which together enable the organism to survive on its own. 8 MEIOSIS Adult METAMORPHOSIS Larva 7 Inner cell layer (endoderm) Internal sac 1 Egg Digestive tract Outer cell layer (ectoderm) Later gastrula (cross section) Zygote (fertilized egg) Eight-cell stage Blastula (cross section) 6 MITOSIS Early gastrula (cross section) Future middle layer of cells (mesoderm) Key Haploid (n) Diploid (2n) Chapter 8 Outline 7 Biology and Society: Virgin Birth of a Dragon 8 What Cell Reproduction Accomplishes The Cell Cycle and Mitosis Meiosis, The Basis of Sexual Reproduction In 2002, zookeepers at the Chester Zoo were surprised to discover that their Komodo Dragon laid eggs. The female dragon had not been in the company of a male. The eggs developed without fertilization, in a process called parthenogenesis. DNA analysis confirmed that her offspring had genes only from her.

3 Biology and Society: Virgin Birth of a Dragon A second European Komodo dragon is now known to have reproduced asexually, via parthenogenesis, and sexually. 9 Figure WHAT CELL REPRODUCTION ACCOMPLISHES Before a parent cell splits into two, it duplicates its, the structures that contain most of the cell s DNA. During cell division, each daughter cell receives one identical set of from the lone, original parent cell. 11 WHAT CELL REPRODUCTION ACCOMPLISHES Cell division plays important roles in the lives of organisms. Cell division replaces damaged or lost cells, permits growth, and allows for reproduction. 12

4 Figure 8.1a 14 WHAT CELL REPRODUCTION ACCOMPLISHES 15 In asexual reproduction, FUNCTIONS OF CELL DIVISION Cell Replacement Growth via Cell Division single-celled organisms reproduce by simple cell division and there is no fertilization of an egg by a sperm. Human kidney cell LM Early human embryo Colorized SEM Some multicellular organisms, such as sea stars, can grow new individuals from fragmented pieces. Growing a new plant from a clipping is another example of asexual reproduction. Figure 8.1b 16 WHAT CELL REPRODUCTION ACCOMPLISHES 17 FUNCTIONS OF CELL DIVISION Asexual Reproduction In asexual reproduction, the lone parent and its offspring have identical genes. Mitosis is the type of cell division responsible for asexual reproduction and growth and maintenance of multicellular organisms. LM Division of an amoeba Regeneration of a sea star Growth of a clipping

5 WHAT CELL REPRODUCTION ACCOMPLISHES 18 THE CELL CYCLE AND MITOSIS 19 Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis. Thus, sexually reproducing organisms use meiosis for reproduction and In a eukaryotic cell, most genes are located on in the cell nucleus and a few genes are found in DNA in mitochondria and chloroplasts. mitosis for growth and maintenance. Eukaryotic Chromosomes 20 Figure 8.2 Species Number of in body cells 21 Each eukaryotic chromosome contains one very long DNA molecule, typically bearing thousands of genes. Indian muntjac deer Koala Opossum The number of in a eukaryotic cell depends on the species. Giraffe Mouse Human 46 Duck-billed platypus 54 Buffalo 60 Dog 78 Red viscacha rat 102

6 Eukaryotic Chromosomes 22 Figure Chromosomes are made of chromatin, fibers composed of roughly equal amounts of DNA and protein molecules and not visible in a cell until cell division occurs. LM Chromosomes Eukaryotic Chromosomes The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding. Histones are proteins used to package DNA in eukaryotes. Nucleosomes consist of DNA wound around histone molecules. Animation: DNA Packing Right click slide / select Play

7 Figure Eukaryotic Chromosomes 27 DNA double helix Beads on a string Histones Before a cell divides, it duplicates all of its, resulting in two copies called sister chromatids containing identical genes. TEM Nucleosome Two sister chromatids are joined together tightly at a narrow waist called the centromere. Tight helical fiber Thick supercoil Duplicated (sister chromatids) Centromere TEM Eukaryotic Chromosomes 28 Figure When the cell divides, the sister chromatids of a duplicated chromosome separate from each other. Once separated, each chromatid is considered a full-fledged chromosome and identical to the original chromosome. Chromosome duplication Sister chromatids Chromosome distribution to daughter cells

8 The Cell Cycle 30 Figure 8.6 S phase (DNA synthesis; chromosome duplication) 31 A cell cycle is the ordered sequence of events that extend from the time a cell is first formed from a dividing parent cell Interphase: metabolism and growth (90% of time) G 1 G 2 Mitotic (M) phase: cell division (10% of time) to its own division into two cells. The cell cycle consists of two distinct phases: 1. interphase and 2. the mitotic phase. Cytokinesis (division of cytoplasm) Mitosis (division of nucleus) The Cell Cycle 32 The Cell Cycle 33 Most of a cell cycle is spent in interphase. During interphase, a cell performs its normal functions, The mitotic (M) phase includes two overlapping processes: 1. mitosis, in which the nucleus and its contents divide evenly into two daughter nuclei and doubles everything in its cytoplasm, and grows in size. 2. cytokinesis, in which the cytoplasm is divided in two.

9 Mitosis and Cytokinesis 34 Mitosis and Cytokinesis 35 During mitosis the mitotic spindle, a footballshaped structure of microtubules, guides the separation of two sets of daughter. Mitosis consists of four distinct phases: 1. Prophase Spindle microtubules grow from structures within the cytoplasm called centrosomes Bioflix Animation: Mitosis Video: Animal Mitosis

10 Figure 8.7a INTERPHASE PROPHASE 38 Mitosis and Cytokinesis 39 Centrosomes (with centriole pairs) Chromatin Early mitotic spindle Centrosome Centromere Fragments of nuclear envelope 1. Prophase 2. Metaphase Nuclear envelope Plasma membrane Chromosome (two sister chromatids) Spindle microtubules Figure 8.7b METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS 40 Figure 8.7bb 41 Nuclear envelope forming Cleavage furrow METAPHASE Spindle Daughter

11 Mitosis and Cytokinesis 42 Figure 8.7b METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Prophase 2. Metaphase 3. Anaphase Nuclear envelope forming Cleavage furrow Spindle Daughter Mitosis and Cytokinesis 44 Figure 8.7b METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Prophase 2. Metaphase 3. Anaphase Nuclear envelope forming Cleavage furrow 4. Telophase Spindle Daughter

12 Mitosis and Cytokinesis 46 Mitosis and Cytokinesis 47 Cytokinesis usually In animal cells, cytokinesis begins during telophase, is known as cleavage and divides the cytoplasm, and is different in plant and animal cells. begins with the appearance of a cleavage furrow, an indentation at the equator of the cell. 48 Figure 8.8a 49 SEM Cleavage furrow Cleavage furrow Contracting ring of microfilaments Animation: Cytokinesis Right click slide / select Play Daughter cells

13 Mitosis and Cytokinesis In plant cells, cytokinesis begins when vesicles containing cell wall material collect at the middle of the cell and then fuse, forming a membranous disk called the cell plate. Blast Animation: Cytokinesis in Plant Cells Select Play Figure 8.8b Wall of parent cell Cell plate forming Daughter nucleus 52 Cancer Cells: Growing Out of Control 53 LM Normal plant and animal cells have a cell cycle control system that consists of specialized proteins, which send stop and go-ahead signals at certain key points during the cell cycle. Cell wall Vesicles containing cell wall material Cell plate New cell wall Problems with the cell cycle control system can cause cancer Daughter cells

14 What Is Cancer? 54 What Is Cancer? 55 Cancer is a disease of the cell cycle. Cancer results from a genetic change in one or more genes that encode for proteins in the cell cycle control system Cancer cells do not respond normally to the cell cycle control system. Cancer cells can form tumors, abnormally growing masses of body cells. If the abnormal cells remain at the original site, the lump is called a benign tumor. The spread of cancer cells beyond their original site of origin is metastasis. Malignant tumors can spread to other parts of the body and interrupt normal body functions. A person with a malignant tumor is said to have cancer. Figure Cancer Treatment 57 Tumor Glandular tissue Lymph vessels Blood vessel Cancer treatment can involve radiation therapy, which damages DNA and disrupts cell division, and chemotherapy, the use of drugs to disrupt cell division. A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Metastasis: Cancer cells spread through lymph and blood vessels to other parts of the body.

15 Cancer Prevention and Survival Certain behaviors can decrease the risk of cancer: not smoking, exercising adequately, avoiding exposure to the sun, eating a high-fiber, low-fat diet, performing self-exams, and regularly visiting a doctor to identify tumors early. 58 MEIOSIS, THE BASIS OF SEXUAL REPRODUCTION Sexual reproduction depends on meiosis and fertilization and produces offspring that contain a unique combination of genes from the parents. 59 Figure Homologous Chromosomes 61 Different individuals of a single species have the same number and types of. A human somatic cell is a typical body cell and has 46.

16 Homologous Chromosomes 62 Figure A karyotype is an image that reveals an orderly arrangement of. Pair of homologous LM Homologous are matching pairs of that Centromere can possess different versions of the same genes. One duplicated chromosome Sister chromatids Homologous Chromosomes 64 Gametes and the Life Cycle of a Sexual Organism 65 Humans have two different sex, X and Y, and 22 pairs of matching, called autosomes. The life cycle of a multicellular organism is the sequence of stages leading from the adults of one generation to the adults of the next.

17 Figure 8.12 Haploid gametes (n = 23) 66 Gametes and the Life Cycle of a Sexual Organism 67 n Egg cell n Sperm cell Humans are diploid organisms with body cells containing two sets of and MEIOSIS FERTILIZATION haploid gametes that have only one member of each homologous pair of. Multicellular diploid adults (2n = 46) 2n Diploid zygote (2n = 46) In humans, a haploid sperm fuses with a haploid egg during fertilization to form a diploid zygote. MITOSIS and development Key Haploid (n) Diploid (2n) Gametes and the Life Cycle of a Sexual Organism 68 Figure Sexual life cycles involve an alternation of diploid and haploid stages. 1 Chromosomes duplicate. Meiosis produces haploid gametes, which keeps the chromosome number from doubling every generation. Pair of homologous in diploid parent cell Duplicated pair of homologous Sister chromatids INTERPHASE BEFORE MEIOSIS

18 Figure Figure Chromosomes 2 duplicate. Homologous separate. 1 Chromosomes 2 Homologous 3 duplicate. separate. Sister chromatids separate. Pair of homologous in diploid parent cell Duplicated pair of homologous Sister chromatids Pair of homologous in diploid parent cell Duplicated pair of homologous Sister chromatids INTERPHASE BEFORE MEIOSIS MEIOSIS I INTERPHASE BEFORE MEIOSIS MEIOSIS I MEIOSIS II The Process of Meiosis In meiosis, haploid daughter cells are produced in diploid organisms, interphase is followed by two consecutive divisions, meiosis I and meiosis II, and crossing over occurs. Bioflix Animation: Meiosis

19 Figure 8.14a 74 Figure 8.14b 75 MEIOSIS I: HOMOLOGOUS CHROMOSOMES SEPARATE MEIOSIS II: SISTER CHROMATIDS SEPARATE INTERPHASE PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Centrosomes (with centriole pairs) Sites of crossing over Spindle Microtubules attached to chromosome Sister chromatids remain attached Cleavage furrow Sister chromatids separate Haploid daughter cells forming Sister Nuclear chromatids Pair of envelope Chromatin Centromere homologous Chromosomes duplicate. Homologous pair up and exchange segments. Pairs of homologous line up. Pairs of homologous split up. Two haploid cells form; are still doubled. During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single. Review: Comparing Mitosis and Meiosis 76 Figure 8.15 MITOSIS MEIOSIS 77 In mitosis and meiosis, the duplicate only once, during the preceding interphase. The number of cell divisions varies: Mitosis uses one division and produces two diploid cells. Prophase Duplicated chromosome Metaphase Chromosomes align. Parent cell Prophase I Metaphase I Homologous pairs align. MEIOSIS I Site of crossing over Meiosis uses two divisions and produces four haploid cells. All the events unique to meiosis occur during meiosis I. Anaphase Telophase Sister chromatids separate. 2n 2n Anaphase I Telophase I Homologous separate. Sister chromatids separate. n n n n MEIOSIS I Haploid n = 2 MEIOSIS II

20 Figure 8.15a 78 Figure 8.15b 79 Prophase Duplicated chromosome MITOSIS Prophase I MEIOSIS MEIOSIS I Anaphase Telophase MITOSIS Anaphase I Telophase I MEIOSIS MEIOSIS I Metaphase Chromosomes align. Parent cell Metaphase I Homologous pairs align. Site of crossing over Sister chromatids separate. 2n 2n Homologous separate. Sister chromatids separate. n n n n Haploid n = 2 MEIOSIS II The Origins of Genetic Variation 80 Independent Assortment of Chromosomes 88 Offspring of sexual reproduction are genetically different from their parents and one another. When aligned during metaphase I of meiosis, the side-by-side orientation of each homologous pair of is a matter of chance. Every chromosome pair orients independently of all of the others at metaphase I. For any species, the total number of chromosome combinations that can appear in the gametes due to independent assortment is 2 n, where n is the haploid number.

21 Independent Assortment of Chromosomes For a human, n = 23. With n = 23, there are 8,388,608 different chromosome combinations possible in a gamete. Animation: Genetic Variation Right click slide / select Play 91 Figure POSSIBILITY 1 POSSIBILITY 2 92 Two equally probable arrangements of at metaphase of meiosis I Blast Animation: Genetic Variation: Independent Assortment Select Play

22 Figure POSSIBILITY 1 POSSIBILITY 2 93 Figure POSSIBILITY 1 POSSIBILITY 2 94 Two equally probable arrangements of at metaphase of meiosis I Two equally probable arrangements of at metaphase of meiosis I Metaphase of meiosis II Metaphase of meiosis II Gametes Combination a Combination b Combination c Combination d Because possibilities 1 and 2 are equally likely, the four possible types of gametes will be made in approximately equal numbers. Random Fertilization 95 Figure A human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote. If each gamete represents one of 8,388,608 different chromosome combinations, at fertilization, humans would have 8,388,608 8,388,608, or more than 70 trillion different possible chromosome combinations. So we see that the random nature of fertilization adds a huge amount of potential variability to the offspring of sexual reproduction. Colorized LM

23 Crossing Over In crossing over, nonsister chromatids of homologous exchange corresponding segments and genetic recombination, the production of gene combinations different from those carried by parental, occurs. Animation: Crossing Over Right click slide / select Play 102 Figure 8.18 Prophase I of meiosis Duplicated pair of homologous 103 Homologous chromatids exchange corresponding segments. Chiasma, site of crossing over Metaphase I Sister chromatids remain joined at their centromeres. Spindle microtubule Metaphase II Gametes Blast Animation: Genetic Variation: Fusion of Gametes Select Play Recombinant combine genetic information from different parents. Recombinant

24 Figure 8.18a 104 Figure 8.18b 105 Prophase I of meiosis Duplicated pair of homologous Metaphase II Homologous chromatids exchange corresponding segments. Chiasma, site of crossing over Gametes Metaphase I Sister chromatids remain joined at their centromeres. Spindle microtubule Recombinant combine genetic information from different parents. Recombinant The Process of Science: Do All Animals Have Sex? 106 The Process of Science: Do All Animals Have Sex? 107 Observation: No scientists have ever found male bdelloid rotifers, a microscopic freshwater invertebrate. Hypothesis: Bdelloid rotifers have thrived for millions of years despite a lack of sexual reproduction. Question: Does this entire class of animals reproduce solely by asexual means? Prediction: Bdelloid rotifers would display much more variation in their pairs of homologous genes than most organisms. Experiment: Researchers compared sequences of a particular gene in bdelloid and non-bdelloid rotifers.

25 The Process of Science: Do All Animals Have Sex? Results: Non-bdelloid sexually reproducing rotifers had a nearly identical homologous gene, differing by only 0.5% on average. The two versions of the same gene in asexually reproducing bdelloid rotifers differed by %. Conclusion: Bdelloid rotifers have evolved for millions of years without any sexual reproduction. 108 Figure LM When Meiosis Goes Awry 110 How Accidents during Meiosis Can Alter Chromosome Number 111 What happens when errors occur in meiosis? In nondisjunction, Such mistakes can result in genetic abnormalities that range from mild to fatal. the members of a chromosome pair fail to separate at anaphase, producing gametes with an incorrect number of. Nondisjunction can occur during meiosis I or II.

26 Figure Figure NONDISJUNCTION IN MEIOSIS I NONDISJUNCTION IN MEIOSIS II NONDISJUNCTION IN MEIOSIS I NONDISJUNCTION IN MEIOSIS II Meiosis I Meiosis I Homologous fail to separate. Homologous fail to separate. Meiosis II Sister chromatids fail to separate. Figure NONDISJUNCTION IN MEIOSIS I NONDISJUNCTION IN MEIOSIS II 114 How Accidents during Meiosis Can Alter Chromosome Number 115 Meiosis I Meiosis II Gametes Homologous fail to separate. Sister chromatids fail to separate. If nondisjunction occurs, and a normal sperm fertilizes an egg with an extra chromosome, the result is a zygote with a total of 2n + 1. If the organism survives, it will have an abnormal karyotype and probably a syndrome of disorders caused by the abnormal number of genes. n + 1 n + 1 n 1 n 1 n + 1 n 1 Abnormal Abnormal n n Normal

27 Figure 8.21 Abnormal egg cell with extra chromosome 116 Down Syndrome: An Extra Chromosome 21 Down syndrome 117 is also called trisomy 21, n + 1 is a condition in which an individual has an extra chromosome 21, and affects about one out of every 700 children. Normal sperm cell n (normal) Abnormal zygote with extra chromosome 2n + 1 Figure Figure 8.22a LM 119 LM Trisomy 21 Trisomy 21

28 Figure 8.22b 120 Down Syndrome: An Extra Chromosome The incidence of Down syndrome in the offspring of normal parents increases markedly with the age of the mother. Figure Abnormal Numbers of Sex Chromosomes Infants with Down syndrome (per 1,000 births) Nondisjunction in meiosis can lead to abnormal numbers of sex but seems to upset the genetic balance less than unusual numbers of autosomes, perhaps because the Y chromosome is very small and carries relatively few genes Age of mother

29 Table Evolution Connection: The Advantages of Sex Asexual reproduction conveys an evolutionary advantage when plants are sparsely distributed and unlikely to be able to exchange pollen or superbly suited to a stable environment. Asexual reproduction also eliminates the need to expend energy forming gametes and copulating with a partner. 125 Figure Evolution Connection: The Advantages of Sex 127 Sexual reproduction may convey an evolutionary advantage by speeding adaptation to a changing environment or allowing a population to more easily rid itself of harmful genes. Runner

30 Figure 8.UN Figure 8.UN Chromosome (one long piece of DNA) Duplication of all Distribution via mitosis Centromere Sister chromatids Genetically identical daughter cells Duplicated chromosome Figure 8.UN03 S phase DNA synthesis; chromosome duplication Interphase Cell growth and chromosome duplication 130 Figure 8.UN04 Human Life Cycle Key Haploid (n) Diploid (2n) Haploid gametes (n = 23) n Egg cell n Sperm cell 131 G 1 G 2 Mitotic (M) phase MEIOSIS FERTILIZATION Genetically identical daughter cells Cytokinesis (division of cytoplasm) Mitosis (division of nucleus) Male and female diploid adults (2n = 46) MITOSIS and development 2n Diploid zygote (2n = 46)

31 Figure 8.UN05 MITOSIS MEIOSIS 132 Figure 8.UN Parent cell (2n) Chromosome duplication Parent cell (2n) Chromosome duplication MEIOSIS I Pairing of homologous chromosome (a) (b) LM Crossing over (c) Daughter cells 2n 2n MEIOSIS II (d) n n n Daughter cells n