Chapter 9 Power Point Lectures for Biology Concepts
Chapter 9 Power. Point Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LM 340 The Cellular Basis of Reproduction and Inheritance
• In sexual reproduction – Fertilization of sperm and egg produces offspring • In asexual reproduction – Offspring are produced by a single parent, without the participation of sperm and egg Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION 9. 1 Like begets like, more or less • Some organisms reproduce asexually Figure 8. 1 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LM 340 – And their offspring are genetic copies of the parent and of each other
• Other organisms reproduce sexually – Creating a variety of offspring 8 Figure. 1 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
9. 2 Cells arise only from preexisting cells • Cell division is at the heart of the reproduction of cells and organisms – Because cells come only from preexisting cells Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
9. 3 Prokaryotes reproduce by binary fission • Prokaryotic cells – Reproduce asexually by cell division Colorized TEM 32, 500 Prokaryotic chromosomes Figure 8. 3 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• As the cell Prokaryotic replicates its chromosome single chromosome, the copies move apart Plasma membrane Cell wall – And the growing membrane then divides the cells 3 Figure 8. 3 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 1 Duplication of chromosome and separation of copies 2 Continued elongation of the cell and movement of copies Division into two daughter cells
THE EUKARYOTIC CELL CYCLE AND MITOSIS 9. 4 The large, complex chromosomes of eukaryotes duplicate with each cell division • A eukaryotic cell has many more genes than a prokaryotic cell – And they are grouped into multiple chromosomes in the nucleus Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Individual chromosomes contain a very long DNA molecule associated with proteins called Histones. – And are visible only when the cell is in the process of dividing – Chromosomes occur in the form of thin, loosely packed chromatin fibers Figure 8. 4 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LM 600 • If a cell is not undergoing division
• Before a cell starts dividing, the chromosomes replicate Sister chromatids – Producing sister chromatids joined together at the centromere TEM 36, 000 Centromere Figure 8. 4 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Cell division involves the separation of sister chromatids – And results in two daughter cells, each containing a complete and Centromere identical set of chromosomes Chromosome duplication Sister chromatids Chromosome distribution to daughter cells Figure 8. 4 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
9. 5 The cell cycle multiplies cells • The cell cycle consists of two major phases INTERPHASE G 1 S (DNA synthesis) is M yto C MI PH TOTIC AS E( M) ito sis es kin Figure 8. 5 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings G 2
• During interphase – Chromosomes duplicate and cell parts are made • During the mitotic phase – Duplicated chromosomes are evenly distributed into two daughter nuclei Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
9. 6 Cell division is a continuum of dynamic changes • In mitosis, after the chromosomes coil up – A mitotic spindle moves them to the middle of the cell Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The sister chromatids then separate – And move to opposite poles of the cell, where two nuclei form Cytokinesis, in which the cell divides in two • Overlaps the end of mitosis Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LM 250 • The stages of cell division INTERPHASE PROPHASE Centrosomes (with centriole pairs) Chromatin Early mitotic spindle PROMETAPHASE Centrosome Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Chromosome, consisting Plasma membrane ot two sister chromatids Figure 8. 6 (Part 1) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Centromere Spindle microtubules
ANAPHASE METAPHASE Cleavage furrow Metaphase plate Spindle TELOPHASE AND CYTOKINESIS Daughter chromosomes Figure 8. 6 (Part 2) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Nuclear envelope forming Nucleolus forming
9. 7 Cytokinesis differs for plant and animal cells • In animals Cleavage furrow Figure 8. 7 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings SEM 140 – Cytokinesis occurs by a constriction of the cell (cleavage) Contracting ring of microfilaments Daughter cells
• In plants Cell plate forming Wall of parent cell Daughter nucleus TEM 7, 500 – A membranous cell plate splits the cell in two Cell wall Vesicles containing cell wall material Figure 8. 7 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings New cell wall Cell plate Daughter cells
9. 8 Anchorage, cell density, and chemical growth factors affect cell division • Most animal cells divide – Only when stimulated, and some not at all Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• In laboratory cultures – Most normal cells divide only when attached to a surface • They continue dividing – Until they touch one another Figure 8. 8 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cells anchor to dish surface and divide. When cells have formed a complete single layer, they stop dividing (densitydependent inhibition). If some cells are scraped away, the remaining cells divide to fill the dish with a single layer and then stop (density-dependent inhibition).
• Growth factors – Are proteins secreted by cells that stimulate other cells to divide After forming a single layer, cells have stopped dividing. Providing an additional supply of growth factors stimulates further cell division. Figure 8. 8 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
9. 9 Growth factors signal the cell cycle control system • A set of proteins within the cell – Controls the cell cycle Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Signals affecting critical checkpoints in the cell cycle – Determine whether a cell will go through the complete cycle and divide G 1 checkpoint G 0 Control system G 1 M Figure 8. 9 A G 2 M checkpoint G 2 checkpoint Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings S
• The binding of growth factors to specific receptors on the plasma membrane – Is usually necessary for cell division. Growth factor Plasma membrane Receptor protein Signal transduction pathway Relay proteins G 1 checkpoint Control system G 1 M Figure 8. 9 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings G 2 S
CONNECTION 9. 10 Growing out of control, cancer cells produces malignant tumors • Cancer cells – divide excessively to form masses called tumors Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Malignant tumors – Can invade other tissues Lymph vessels Tumor Blood vessel Glandular tissue A tumor grows from a single cancer cell. Cancer cells invade neighboring tissue. Figure 8. 10 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Cancer cells spread through lymph and blood vessels to other parts of the body.
• Radiation and chemotherapy – Are effective as cancer treatments because they interfere with cell division Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
9. 11 Review of the functions of mitosis: Growth, cell replacement, and asexual reproduction • When the cell cycle operates normally, mitotic cell division functions in Figure 8. 11 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings LM 500 – Growth
LM 700 • Replacement of damaged or lost cells Figure 8. 11 B Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
MEIOSIS AND CROSSING OVER 9. 12 Chromosomes are matched in homologous pairs • The somatic (body) cells of each species – Contain a specific number of chromosomes • For example human cells have 46 – Making up 23 pairs of homologous chromosomes Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The chromosomes of a homologous pair – Carry genes for the same characteristics at the same place, or locus Chromosomes Centromere Figure 8. 12 Sister chromatids Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
9. 13 Gametes have a single set of chromosomes • Cells with two sets of chromosomes – Are said to be diploid • Gametes, eggs and sperm, are haploid – With a single set of chromosomes Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Sexual life cycles – Involve the alternation of haploid and diploid stages Haploid gametes (n = 23) n Egg cell n Sperm cell Meiosis Fertilization Multicellular diploid adults (2 n = 46) Diploid zygote (2 n = 46) Mitosis and development Figure 8. 13 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 2 n
9. 14 Meiosis reduces the chromosome number from diploid to haploid • Meiosis, like mitosis – Is preceded by chromosome duplication • But in meiosis – The cell divides twice to form four daughter cells Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The first division, meiosis I – Starts with synapsis, the pairing of homologous chromosomes • In crossing over – Homologous chromosomes exchange corresponding segments • Meiosis I separates each homologous pair – And produce two daughter cells, each with one set of chromosomes Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Meiosis II is essentially the same as mitosis – The sister chromatids of each chromosome separate – The result is a total of four haploid cells Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• The stages of meiosis MEIOSIS I: Homologous chromosomes separate INTERPHASE Centrosomes (with centriole pairs) Nuclear envelope PROPHASE I METAPHASE I Sites of crossing over Spindle Chromatin Sister chromatids Tetrad Figure 8. 14 (Part 1) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Microtubules Metaphase attached to plate kinetochore Centromere (with kinetochore) ANAPHASE I Sister chromatids remain attached Homologous chromosomes separate
MEIOSIS II: Sister chromatids separate TELOPHASE I AND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS Cleavage furrow Sister chromatids separate Figure 8. 14 (Part 2) Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Haploid daughter cells forming
9. 15 Review: A comparison of mitosis and meiosis Mitosis Meiosis Parent cell (before chromosome replication) Meiosis i Prophase I Prophase Duplicated chromosome (two sister chromatids) 2 n = 4 Metaphase Chromosomes align at the metaphase plate Tetrads align at the metaphase plate Anaphase Telophase Sister chromatids separate during anaphase Homologous chromosomes separate during anaphase I; sister chromatids remain together 2 n Daughter cells of mitosis Tetrad formed by synapsis of homologous chromosomes Chromosome replication 2 n Figure 8. 15 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings No further chromosomal replication; sister chromatids separate during anaphase II Metaphase I Anaphase I Telophase I Haploid n=2 Daughter cells of meiosis I Meiosis ii n n Daughter cells of meiosis II
9. 18 Crossing over further increases genetic variability – Which results from crossing over during prophase I of meiosis, increases variation Tetrad still further TEM 2, 200 • Genetic recombination Chiasma Centromere Figure 8. 18 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE 9. 19 A karyotype is a photographic inventory of an individual’s chromosomes • A karyotype – Is an ordered arrangement of a cell’s chromosomes Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Preparation of a karyotype from a blood sample Hypotonic solution Packed red and white blood cells Fixative Stain Blood culture White blood cells Centrifuge 1 A blood Fluid culture is centrifuged to separate the blood cells from the culture fluid. 2 The fluid is discarded, and a hypotonic solution is mixed with the cells. This makes the red blood cells burst. The white blood cells swell but do not burst, and their chromosomes spread out. 3 Another centrifugation step separates the swollen white blood cells. The fluid containing the remnants of the red blood cells is poured off. A fixative (preservative) is mixed with the white blood cells. A drop of the cell suspension is spread on a microscope slide, dried, and stained. Centromere Sister chromosomes 2, 600 X Pair of homologous chromosomes 4 The slide is viewed with a microscope equipped with a digital camera. A photograph of the chromosomes is entered into a computer, which electronically arranges them by size and shape. Figure 8. 19 Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 5 The resulting display is the karyotype. The 46 chromosomes here include 22 pair of autosomes and 2 sex chromosomes, X and Y. Although difficult to discern in the karyotype, each of the chromosomes consists of two sister chromatids lying very close together (see diagram).
CONNECTION 9. 20 An extra copy of chromosome 21 causes Down syndrome • A person may have an abnormal number of chromosomes – Which causes problems Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Down syndrome is caused by trisomy 21 5, 000 – An extra copy of chromosome 21 Figure 8. 20 A Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings Figure 8. 20 B
• The chance of having a Down syndrome child – Goes up with maternal age Infants with Down syndrome (per 1, 000 births) 90 80 70 60 50 40 30 20 10 0 20 25 Figure 8. 20 C Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings 30 35 40 Age of mother 45 50
9. 21 Accidents during meiosis can alter chromosome number • Abnormal chromosome count is a result of nondisjunction – The failure of homologous pairs to separate during meiosis I – The failure of sister chromatids to separate during meiosis II Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
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