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Points to ponder What is the cell cycle and what occurs during each of its stages? Explain what mitosis is used for, what cells undergo mitosis, and the four stages of mitosis.
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The cell cycle 2 parts: Interphase:
G1 stage – cell doubles its organelles; cell grows in size S stage – DNA replication occurs G2 stage – proteins needed for division are synthesized Cell division (mitosis and cytokinesis): Mitosis – nuclear division Cytokinesis – cytoplasmic division
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The cell cycle S G2 G1 Mitosis Interphase growth and DNA replication
growth and final preparations for division growth M Mitosis Cytokinesis Telophase Prophase Anaphase Metaphase
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Chromosome structure in mitosis
Chromosomes contain both DNA and proteins (collectively called chromatin) Chromosomes that are dividing are made up of 2 identical parts called sister chromatids The sister chromatids are held together at a region called the centromere sister chromatids replication centromere chromosome duplicated chromosome division
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Overview of mitosis A diploid cell makes exact copies of its DNA (chromosomes) during interphase Used for organismal growth, repair, replacement Occurs in body cells 4 phases: Prophase Metaphase Anaphase Telophase centrosome centriole chromosome 2n = 4 DNA REPLICATION DURING INTERPHASE duplicated chromosome consisting of two sister chromatids centromere 2n = 4 MITOSIS 2n = 4 2n = 4
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1. Mitosis: Prophase Chromosomes condense and become visible
Nuclear envelope fragments and disappears Centrioles move to opposite poles Spindle fibers appear and attach to the centromere Early Prophase Centrosomes have duplicated. Chromatin is condensing into chromosomes, and the nuclear envelope is fragmenting. Prophase Nucleolus has disappeared, and duplicated chromosomes are visible. Centrosomes begin moving apart, and spindle is in process of forming. nuclear envelope fragments aster 20 μm Chromatin condenses. Nucleolus disappears. spindle fibers forming duplicated chromosomes centromere
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2. Mitosis: Metaphase Chromosomes line up at the middle of the cell (equator) spindle chromosomes at equator pole centromere spindle fiber Early Metaphase Each chromatid is attached to a spindle fiber. Some spindle fibers stretch from each spindle pole and overlap. Metaphase Centromeres of duplicated chromosomes Area ligned at the equator (center of fully formed spindle). Spindle fibers attached to the sister chromatids come from opposite spindle poles.
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3. Mitosis: Anaphase Sister chromatids separate at the centromeres and move towards the poles daughter chromosome spindle fiber Anaphase Sister chromatids part and become daughter chromosomes that move toward the spindle poles. In this way, each pole receives the same number and kinds of chromosomes as the parental cell.
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4. Mitosis:Telophase and cytokinesis
Chromosomes at opposite poles and decondense (become chromatin again) Nuclear envelope reassembles Cellular material sepatates (cytokinesis) Two daughter cells are formed cleavage furrow Telophase Daughter cells are forming as nuclear envelopes and nucleoli reappear. Chromosomes will become indistinct chromatin.
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Fig. 18.4 A Normal cell cycle
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Cancerous cell cycle One or more checkpoints are inactive or ineffective.
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Characteristics of cancer cells
Lack differentiation and do not contribute to body functioning Have abnormal nuclei or abnormal number of chromosomes Unlimited ability to divide Don’t know how to perform apoptosis Form tumors Benign tumors are usually encapsulated and do not invade adjacent tissue Malignant tumor usually is not encapsulated and eventually invades surrounding tissue
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The 3 phases in the development of cancer cells
epithelial cells 1 mutation a. Cell (dark pink) acquires a mutation for repeated cell division. Initiation – a single cell undergoes a mutation that causes it to divide repeatedly Promotion – a tumor develops and cells within the tumor mutate Progression – a cell mutates in such a way that allows it to invade surrounding tissue Metastasis - cells move into the bloodstream or lymphatic vessels to make new tumors at distant sites from the primary tumor 2 mutations b. New mutations arise, and one cell (brown) has the ability to start a tumor. 3 mutations tumor c. Cancer insitu. The tumor is at its place of origin .One cell (purple) mutates further. lymphatic vessel blood vessel invasive tumor d. Cells have gained the ability to invade underlying tissues by producing a proteinase enzyme. malignant tumor e. Cancer cells now have the ability to invade lymphatic and blood vessels. distant tumor f. New metastatic tumors are found some distance from the original tumor. lymphatic vessel
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Types of cancer Causes of cancer Oncology – study of cancer
Carcinomas: cancers of the epithelial tissue Sarcomas: cancers of muscle and connective tissues Leukemias: cancers of the blood Lymphoma: cancers of lymphatic tissues Causes of cancer Genetics Radiation Environmental carcinogens (tobacco smoke and pollutants) Viruses
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Estimated cases of cancer and cancer deaths in the United States
Male Female Male Female prostate 25% breast 27% lung and bronchus 30% lung and bronchus 26% lung and bronchus 15% lung and bronchus 14% colon and rectum 9% breast 15% colon and rectum 10% colon and rectum 10% prostate 9% colon and rectum 9% urinary bladder 7% uterine corpus 6% pancreas 6% pancreas 6% melanoma of the skin 5% non-hodgkin lymphoma 4% leukemia 4% ovary 5% non-hodgkin lymphoma 5% melanoma of the skin 4% liver and intrahepatic bile duct 4% non-hodgkin lymphoma 4% kidney and renal pelvis 5% thyroid 4% esophagus 4% leukemia 3% oral cavity 3% ovary 3% non-hodgkin lymphoma 3% uterine corpus 3% leukemia 3% kidney and renal pelvis 3% urinary bladder 3% liver and intrahpatic bile duct 2% pancreas 3% pancreas 3% kidney and renal pelvis 3% all other sites 19% all other sites 22% all other sites 25% all other sites 25% all sites 766,130 all sites 713,220 all sites 292,540 all sites 269,800 a. Cancer cases by site and sex b. Cancer deaths by site and sex 17
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Treatment of cancer Surgery—removal of small cancers like skin cancers. Radiation—localized therapy causes chromosomal breakage and cell cycle disruption. Chemotherapy—treats the entire body with drugs that kill cells by damaging their DNA or interfering with DNA synthesis. Bone marrow transplants—sometimes done in conjunction with chemotherapy.
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