Chapter 8 The Cellular Basis of Reproduction Inheritance
Chapter – 8 The Cellular Basis of Reproduction & Inheritance – Mitosis 1
Outline l The Cell Cycle l Interphase l Mitotic Stage l Cell Cycle Control l Apoptosis l Mitosis & Cytokinesis l Mitosis in Animal Cells l The Cell Cycle & Cancer l Prokaryotic Cell Division 2
The Cell Cycle l An orderly set of stages. l The two major stages of the cell cycle: a. Interphase l The cell grows larger l The number of organelles doubles l The DNA is replicated b. Mitosis and Cytokinesis 3
The Cell Cycle Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Interphase S (growth and DNA replication) as La te h op pr ase Metaph Tel o ph as e Anapha se ne ki to y C e M s si Pr G 0 G 1 (growth) G 2 (growth and final preparations for G 2 division) e G 1 o p ha s G 1 checkpoint Cell cycle main checkpoint. If DNA is damaged, apoptosis will occur. Otherwise, the cell is committed to divide when growth signals are present and nutrients are available. G 2 checkpoint Mitosis checkpoint. Mitosis will occur if DNA has replicated properly. Apoptosis will occur if the DNA is damaged and cannot be repaired. M M checkpoint Spindle assembly checkpoint. Mitosis will not continue if chromosomes are not properly aligned. 4
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Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http: //get. adobe. com/flashplayer. 6
Interphase consists of: G 1, S and G 2 phases l G 1 Phase: l l l S Phase: l l l Cell doubles its organelles Cell grows in size DNA replication Chromosomes leave with 2 identical chromatids each G 2 Phase: l l Cell grows in size and prepares for mitosis 7
Mitotic (M) Stage l Includes: l l Nuclear division (karyokinesis) l Daughter chromosomes distributed to two daughter nuclei Cytokinesis l Cytoplasm division l Results in two genetically identical daughter cells 8
Mitosis: Preparation l DNA is in very long threads l Chromosomes l Stretched out and intertangled between divisions l DNA is associated with histone proteins l Collectively called ‘chromatin’. 9
l Before mitosis begins: l Chromatin condenses (coils) into distinctly visible chromosomes l Each species has a characteristic chromosome number l l l Humans 46 Corn 20 Goldfish 94 10
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Chromosome Number Diploid (2 n) number includes two sets of chromosomes. Humans have 23 pair of chromosomes in each body cell, making a total of 46 in each nucleus. One set of 23 is coming from father (paternal) and other set of 23 Is coming from mother (maternal). Haploid (n) number include one set of chromosome. Only sperm and eggs have 23 chromosomes (haploid set). 12
A karyotype is an organized profile of a person's chromosomes. In a karyotype, chromosomes are arranged by size, from largest to smallest. An autosome is a non- sex chromosome. For example, in human, there are twenty-two pairs of autosomes, and a pair of sex chromosomes (XX or XY). 13
Chromosome Numbers of Some Eukaryotes Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 14
Chromosome Structure l At end of S phase: l Each chromosome internally duplicated l Consists of two identical DNA chains l Sister chromatids (two strands of genetically identical chromosomes) l Attached together at a single point (called centromere) 15
Mitosis in Animal Cells Just outside nucleus is the centrosome. (This is the microtubule organizing center). l In animals, it contains two barrel-shaped centrioles, oriented at right angles to each other and each composed of a bundle of microtubules. l Centrosome will be replicated in S-phase, resulting in two centrosomes. Just before mitosis, the two centrosomes move apart until they are on opposite sides of the nucleus. l 16
Mitosis in Animals and Plants 17
Mitosis in Animal Cells: Prophase l Two sister chromatids attached at centromere are clearly visible. l Nucleolus disappears l Nuclear envelope disintegrates l Centriole will produce spindle fibers or the mitotic spindles. Microtubules grow out from each centrosome with their ends growing toward the metaphase plate. These clusters of microtubules are called spindle fibers. 18
Mitosis in Animal Cells: Prometaphase Centromere of each chromosome develops two kinetochores, specialized protein complex, over each sister chromatid, they physically hook sister chromatids with microtubules. 19
Mitosis in Animal Cells: Metaphase Chromosomes, (made up of sister chromatids), are pulled around by kinetochore (spindle) fibers and forced to align across equatorial plane (metaphase plate) of cell. 20
Mitosis in Animal Cells: Anaphase Centromere breaks in the middle, releasing sister chromatids. Sister chromatids separate and are pulled to Opposite poles by the contraction of the spindle fiber. Each sister chromatid is now called daughter chromosomes. 21
Mitosis in Animal Cells: Telophase Spindle disappears. Two clusters of chromosomes are resulted. Around each cluster, nuclear envelopes form. Chromosomes uncoil and become chromatin again. Nucleolus reappears Resulting in two daughter nuclei inside a parent cell. 22
Cytokinesis: Animal Cells Division of mother cell’s cytoplasm into two. Often begins in anaphase Animal cytokinesis: l l l A cleavage furrow appears between daughter nuclei (Formed by a contractile ring of actin filaments) Eventually pinches mother cell in two 23
Cytokinesis: Plant Cells – Cell Plate formation Many small membrane-bounded vesicles are formed in the middle of the parent cell and they extend towards the periphery. Vesicles fuse to form a cell plate. The membranes of the cell plate become the plasma membrane between the daughter cells. Contents of vesicles become the middle lamella between the two daughter cells. On opposite sides of middle lamella, daughter cells later secrete primary cell walls. 24
Function of Mitosis l l Permits growth and repair. Allows a cut to heal or a broken bone to mend In plants, it helps to divide throughout the life of the plant. In mammals, mitosis is necessary for embryo becomes a fetus 25
The Cell Cycle and Cancer l Abnormal growth of cells is called a neoplasm l Benign neoplasms are not cancerous l Do not invade neighboring tissue or spread l Malignant neoplasms are cancerous l Readily invade neighboring tissues l development of cancer (carcinogenesis) is gradual, may take years before cell becomes cancerous 26
Characteristics of Cancer Cells Lack differentiation l Have abnormal nuclei l Form tumors l 27
Prokaryotic Cell Division - Binary fission (Asexual Reproduction) Prokaryotic cell contains a ring shaped DNA in nucleoid region; DNA attaches to the plasma membrane; DNA replicates into two rings; Replicated 2 DNA rings migrate towards opposite poles; Formation of septum between the 2 replicated DNA, dividing the parent cell; Produces two daughter cells identical to original cell. 28
Review l The Cell Cycle l Interphase l Mitotic Stage l Cytokinesis l Mitosis in Animal cells and Plant cells l The Cell Cycle & Cancer l Prokaryotic Cell Division 29
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