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The Cell Cycle and Cellular Reproduction Chapter 9 Cell Cycle Cell Cycle – the orderly set of stages in life of cell between cell division and division of the daughter cells Can be separated into 2 phases: Interphase Mitosis Mader; Biology, 9th Ed. Cell Cycle Interphase Includes the normal functioning of the cell Represents the major part of the cell cycle in most normal cells Consists of 3 phases: G1 S G2 Mader; Biology, 9th Ed. Cell Cycle Mader; Biology, 9th Ed. Interphase G1 Stage Before DNA replication Protein synthesis Preparation for DNA replication Duplication of organelles S stage S – DNA synthesis Duplication of chromosomes G2 Stage Second gap phase Protein synthesis Prep for cell division (M Stage) Mader; Biology, 9th Ed. Mitosis M Stage Mitosis Nuclear division Daughter chromosomes distributed to two daughter nuclei Cytokinesis Cell division Results in two genetically identical daughter cells Mader; Biology, 9th Ed. Control of cell cycle Cell cycle controlled by internal and external signals External signals Growth factors Received at the plasma membrane Cause completion of cell cycle Internal signals Family of proteins called cyclins Increase and decrease as cell cycle continues Without them cycle stops at G1, M or G2 Allows time for any damage to be repaired Mader; Biology, 9th Ed. Control of cell cycle Mader; Biology, 9th Ed. Cell Cycle Essential part of cell life cycle cell death Cells die in 2 ways: Apoptosis Necrosis Mader; Biology, 9th Ed. Apoptosis Apoptosis – programmed cell death Necessary for normal growth and development of organism Development Damaged cells Mader; Biology, 9th Ed. Apoptosis Controlled by internal and external factor Ex. Mitochondrial damage Ex. Fas-Fas ligand interaction Caspase cascade Mader; Biology, 9th Ed. Apoptosis Mader; Biology, 9th Ed. Preparation for Mitosis DNA ordinarily exists within the nucleus as a tangled mass of chromatin DNA associated with histone proteins Prior to mitosis the DNA condenses into chromosomes Distinctly visible Mader; Biology, 9th Ed. Mader; Biology, 9th Ed. Chromosomes Each species has a characteristic number of chromosomes Diploid (2n) - Two of each kind Haploid (1n) - One of each kind Mader; Biology, 9th Ed. Chromosomes Two identical chromatids are called sister chromatids Attached to each other at centromere During nuclear division, sister chromatids separate at the centromeres, and each duplicated chromosome gives rise to two daughter Duplicated chromosome chromosomes Mader; Biology, 9th Ed. Mitosis in Animal Cells Centrosome Outside of nucleus Microtubule organizing center Organizes mitotic spindle Bundle of microtubules Contains a pair of barrel-shaped organelles - centrioles Also contains an array of short microtubules - aster Mader; Biology, 9th Ed. Mitosis in Animal Cells Prophase Chromatin has condensed Nucleolus disappears Nuclear envelope disintegrates Spindle begins to assemble Two centrosomes move away from each other Form microtubules in star-like arrays – asters Mader; Biology, 9th Ed. Mitosis in Animal Cells Prometaphase Kinetochores develop on centromere of each chromosome Specialized protein complex One over each sister chromatid Physically hook sister chromatids up with specialized microtubules (kinetochore fibers) These connect sisters to opposite poles of mother cell Mader; Biology, 9th Ed. Mitosis in Animal Cells Metaphase Chromosomes, attached to kinetochore fibers, are in alignment at center of cell – metaphase plate Mader; Biology, 9th Ed. Mitosis in Animal Cells Anaphase Centromere dissolves, releasing sister chromatids Sister chromatids split, producing daughter chromosomes Daughter chromosomes are pulled to opposite poles Mader; Biology, 9th Ed. Mitosis in Animal Cells Telophase Spindle disappears as new nuclear envelopes form around the daughter chromosomes Chromosomes become diffuse chromatin again Nucleolus appears in each daughter nucleus Mader; Biology, 9th Ed. Mader; Biology, 9th Ed. Cytokinesis Cytokinesis accompanies mitosis in most cells, but not all Mitosis without cytokinesis results in a multinucleated cell Begins in anaphase, continues in telophase, but does not reach completion until the following interphase begins Mader; Biology, 9th Ed. Cytokinesis Animal Cells Cleavage furrow, membrane indentation between daughter nuclei, begins as anaphase nears completion Deepens when a band of actin filaments (contractile ring) forms a circular constriction between the two daughter Mader; Biology, 9th Ed. cells Animal Cell Division Mader; Biology, 9th Ed. Mitosis/Cytokinesis in Plant Cell Meristematic plant tissue retains the ability to divide throughout the plant’s life Found at root and shoot tips Mader; Biology, 9th Ed. Phases of Mitosis in Plant Cells Mader; Biology, 9th Ed. Cytokinesis in Plant Cells Rigid cell wall surrounding plant cells does not permit cytokinesis by furrowing Begins with formation of a cell plate which eventually becomes new plasma membrane between the daughter cells Mader; Biology, 9th Ed. Cytokinesis in Plant Cells Mader; Biology, 9th Ed. Prokaryotic Cell Division Asexual Reproduction - offspring are genetically identical to the parent Binary fission produces two (binary) daughter cells that are identical to the original parent Prokaryotes contain a single chromosome with only a few proteins Mader; Biology, 9th Ed. Prokaryotic Cell Division Mader; Biology, 9th Ed. Cancer Cancer – cellular growth disorder that results from the mutation of genes that regulate the cell cycle Neoplasm – abnormal growth of cells Benign – non-cancerous neoplasm Encapsulated Do not invade neighboring tissue or spread Malignant – cancerous neoplasm Not encapsulated Readily invade neighboring tissues May also detach and lodge in distant places – metastasis Results from mutation of genes regulating the cell cycle Carcinogenesis – development of cancer Mader; Biology, 9th Ed. Characteristics of Cancer Cells Lack differentiation Abnormal nuclei Form tumors Undergo metastasis and angiogenesis Mader; Biology, 9th Ed. Characteristics of Cancer Cells Mader; Biology, 9th Ed. Cervical Cancer http://rds.yahoo.com/S=96062883/K=cervical+cancer+cells/v=2/SID=e/l=IVR/SIG=12aklm0go/ Mader; Biology, 9th Ed. EXP=1127260755/*-http%3A//www.tcd.ie/Histopathology/research/cervical.htm Colon Cancer http://rds.yahoo.com/S=96062883/K=colon+cancer+cells/v=2/SID=e/l=IVR/SIG=12958nea8/EXP=1127261605/*http% Mader; Biology, 9th Ed. 3A//www.bioscience.org/2004/v9/af/1311/figures.htm Origin of Cancer Mutations in DNA repair genes Mutations in proto-oncogenes and tumor-suppressor genes Proto-oncogenes promote the cell cycle in various ways Tumor suppressor genes inhibit the cell cycle in various ways Both normally regulated in coordination with organism’s growth plan If either mutates, may lose control and become oncogene Telomerase Mader; Biology, 9th Ed. Oncogenes Function Oncogenes src Tyrosine kinase ras G protein Oncogene – erb Epidermal growth factor gene that when sis Platelet-derived growth altered or mutated, its factor product is p53* Tumor suppressor responsible for myc* Cell cycle transformation of healthy cells Rb* Tumor suppressor into cancer cells DHAP* Tumor suppressor Often involved in cell cycle ProT* Blocks apoptosis control PETCAM* Tumor suppressor bcl-2* Blocks apoptosis Mader; Biology, 9th Ed. *Involved in control of cell cycle Tumor Supressor Genes Inhibitory to cell cycle Rb - retinoblastoma P53 – Li-Fraumini Mutations Mader; Biology, 9th Ed. Cell Cycle Control Cyclins and Cyclin- dependent kinases (Cdks) Function with tumor- suppressor genes to control cell cycle Mader; Biology, 9th Ed. Cell Cycle Regulation Balance between stimulatory and inhibitory pathways Stimulatory pathway results activation of proto-oncogene which stimulate cell cycle Inhibitory pathway results activation of tumor-suppressor genes which inhibit cell cycle Mader; Biology, 9th Ed. Mader; Biology, 9th Ed. Telomerase Chromosomes normally have excess DNA material at each end called telomeres These get shorter each cell division When they get very short the cell will no longer divide Telomerase is an enzyme that adds telomeres Mutations in telomerase gene: Keeps adding new telomeres Allow cancer cells to continually divide (become “immortalized”) Mader; Biology, 9th Ed. Mader; Biology, 9th Ed.
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