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Michèle Shuster • Janet Vigna • Gunjan Sinha • Matthew Tontonoz Biology for a Changing World FIRST EDITION Intro to Biology Dr. Steve Schwendemann CHAPTER 9 Cell Division and Mitosis Copyright © 2012 by W. H. Freeman and Company Chapter 9 Paramedic Plants Copyright © 2012 by W. H. Freeman and Company Conventional drugs vs. herbal supplements • In conventional drugs, a specific active ingredient is purified from a plant or fungus or synthesized in a laboratory and concentrated into pill, capsule, or injectable form. Conventional drugs vs. herbal supplements • Conventional drugs have been tested in clinical trials and shown to be safe and effective. Conventional drugs vs. herbal supplements • In herbal supplements, plants, algae, fungi, and combinations of these, are used as a tea, an extract, or ground into power and sold in capsule form. – They contain complex mixtures of different unpurified plant molecules. Conventional drugs vs. herbal supplements • Unlike drugs, herbal supplements typically contain several compounds, and they can target diverse biochemical pathways. Conventional drugs vs. herbal supplements • Herbal supplements do not have to be tested in clinical trials. Conventional drugs vs. herbal supplements • There is a lack of consistency in herbal supplements. – Many supplements are contaminated with dangerous heavy metals or bacteria. – The active ingredient in many supplements commonly varies from pill to pill and bottle to bottle. Conventional drugs vs. herbal supplements • The FDA now allows companies to apply to the agency to market an herbal supplement almost like a pharmaceutical drug. – This process requires clinical trial data showing that a supplement works and proof that the company can produce the supplement with consistent quality and quantity from batch to batch. – This is not a mandatory process, but financial incentives are offered. Cell division • Cell division is the process by which a cell reproduces itself. Why do normal, healthy cells divide? • Cell division is important for normal growth, development, and repair of an organism. Why do normal, healthy cells divide? • Cells divide for growth and development. Why do normal, healthy cells divide? • Cells divide for cell replacement. Why do normal, healthy cells divide? • Cells divide to heal wounds. How do cells divide? • A cell doesn’t simply split in half to form two new cells. – If it did, each new cell would be smaller than the original cell, and each cell would lose half of its contents with each division. How do cells divide? • Before a cell divides, it makes a copy of its contents so that each new cell has the same amount of organelles, DNA, and cytoplasm as the original cell. How do cells divide? • Through cell division, one parent cell divides into two new daughter cells, each of which is identical to the parent cell. The cell cycle • The cell cycle is an ordered sequence of stages through which a cell progresses in order to divide during its life. • The purpose of the cell cycle is to replicate cells. Stages of the cell cycle • The cell cycle consists of preparatory phases (collectively know as interphase) and division phases (mitosis and cytokinesis). Stages of the cell cycle: Interphase • Interphase is the stage of the cell cycle in which cells spend most of their time, preparing for cell division. Stages of the cell cycle: Interphase • Interphase is divided into three stages: G1, S, and G2. Stages of the cell cycle: Interphase • During the G1 Phase of interphase, the cell grows and prepares to divide both its DNA and its organelles. Stages of the cell cycle: Interphase • During the S Phase of interphase, DNA replication occurs. Stages of the cell cycle: Interphase • During the G2 Phase of interphase, the cell prepares for division. Stages of the cell cycle: Mitosis • During mitosis, the sister chromatids of each chromosome are separated from one another, setting up the two identical nuclei of the daughter cells. Cell division: The chromosome perspective • Chromosomes are duplicated during the S Phase of interphase. Cell division: The chromosome perspective • A sister chromatid is one of the two identical DNA molecules that make up a duplicated chromosome following DNA replication. Cell division: The chromosome perspective • The sister chromatids are joined together at a region of the chromosome known as the centromere. Cell division: The chromosome perspective • During mitosis and cytokinesis, the sister chromatids pull apart and move into separate daughter cells. Stages of the cell cycle: Cytokinesis • During cytokinesis, the cytoplasm divides into two cells, each containing a full complement of organelles and DNA. Up Close: The phases of mitosis • Mitosis occurs in a series of phases that are part of the cell cycle. Up Close: The phases of mitosis • In interphase, the chromosomes are loosely gathered in the nucleus. Up Close: The phases of mitosis • In prophase, replicated chromosomes begin to coil up, the nuclear membrane begins to disassemble, and the protein fibers of the mitotic spindle begin to form. Up Close: The phases of mitosis • In prometaphase, the chromosomes condense to shorten them, and spindle fibers attach to the chromosomes on both sides at the centromere region. Up Close: The phases of mitosis • In metaphase, spindle fibers from opposite ends of the cell pull on chromosomes, aligning them along the middle of the cell. Up Close: The phases of mitosis • In anaphase, spindle fibers shorten and pull sister chromatids to opposite ends of the cell. Up Close: The phases of mitosis • In telephase, an identical set of chromosomes reaches each pole, the spindle fibers dissemble, and a nuclear membrane forms around each set of chromosomes to form the daughter cell nuclei. Up Close: The phases of mitosis • During cytokinesis, the cell membrane pinches in to completely surround each new daughter cell. • The cell cycle starts over with two newly formed identical daughter cells in interphase. Each daughter cell has the same number of chromosomes as the parent cell. Cell division is tightly regulated • Cell cycle checkpoints ensure that each stage of the cell cycle is completed accurately by preventing a cell from progressing to the next stage until it accurately finishes the current stage. Cell division is tightly regulated • When a normal cell has irreparable damage, it undergoes apoptosis, or programmed cell death to prevent cells from producing more damaged daughter cells. What is cancer? • Cancer is a disease of unregulated cell division. Cells divide inappropriately and accumulate, in some instances forming a tumor. Comparing cancer cells to normal cells • Cancer cells have damaged checkpoint mechanisms, allowing them to divide when they should not. The damaged cells also bypass apoptosis, passing the damaged DNA to each daughter cell. Fighting cancer: Surgery • Surgery to remove the cancerous tumor is effective for certain solid tumors, but it is not an effective treatment for blood cancers or cancers that have undergone metastasis – the spread of cancer cells from one location in the body to another. Fighting cancer: Chemotherapy • Chemotherapy uses drugs to interfere with cell division to treat cancer. Fighting cancer: Radiation therapy • In radiation therapy, high-energy radiation beams are used to kill dividing cells, severely damaging molecules and DNA to trigger apoptosis. Fighting cancer: Side-effects • The side-effects of chemotherapy and radiation therapy can be quite severe. • Herbal supplements may complement cancer treatment by reducing the severity of traditional sideeffects and enhancing the effect of chemotherapy.