Download AP Biology – PowerPoint Notes – Chapter 9

AP Biology – PowerPoint Notes – Chapter 9 ‐ Cellular Reproduction and the Cell Cycle Chromosomes 
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Humans have 46 chromosomes in their somatic cells (2n = diploid) but have haploid (n) in sex cells. Histones Mitosis 
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Cell division is called mitosis. For single celled organisms, mitosis increases the number of individuals. For multi‐celled organisms, mitosis adds to growth, differentiation and repair. Approximately 10 trillion cells in the human body all arose from a single cell by mitosis. o E.g., red blood cells are made at the rate of one million per second Mitosis has two basic functions 
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Duplicate the parent cell Ensure that each daughter cell has a complete copy of the DNA The basic steps are: o Duplicate the DNA o Divide the chromosomes into two complete sets o Divide the cell into two daughter cells The Cell Cycle 
The cell cycle consists of mitosis (10%) and interphase (90%) Stages of mitosis o
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Interphase Prophase Metaphase Anaphase Telophase Cytokenisis Interphase 
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Includes all cell activity between mitotic divisions such as cell growth and normal cell activity Cells prepare for mitosis by synthesizing enough cytoplasm for the daughter cells Centrioles are duplicated DNA replicated Prophase 
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The chromosomes shorten and thicken Centrioles move to opposite poles of the cell Spindle fibers are constructed to extend from the centrioles toward each chromosome Each chromosome is duplicated and the resulting copies are called sister chromatids. They remain attached to one another at a region called the centromere via their kinetochore The nuclear membrane is dissolved Nucleolus disappears Metaphase 
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During late prophase chromatids begin to move toward the cell equator (metaphase plate) At metaphase the chromatids are aligned at the equator Anaphase 
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Chromatids begin to move apart, toward opposite poles Once separated, the chromatids are again called chromosomes Telophase 
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The chromosomes reach opposite poles of the cell Spindle fibers dissolve Nuclear membrane reforms at each end of the cell Nucleolus reappears Centrioles disappear Cytokinesis 
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The division of cytoplasm after separation of the chromosomes In plant cells, a new cell wall forms to divide the two daughter cells In animal cells the cleavage furrow forms as the cell membrane is pinched inward to divide the cell into two daughter cells Differentiation 
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Cell differentiation allows specialization and division of labor. o E.g., a skin cell never becomes any other type of cell Each cell has all the instructions to produce a whole human A cell remains a specific type because of the information it receives from nearby cells and/or the external environment. The signals that trigger cell differentiation are not yet understand Differentiated cells perform selected tasks for the organism and ensure that a multicellular organism is as efficient as a unicellular one 
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For multicellular organisms, development occurs as the number and variety of differentiated cells increases As the number of cells increases, groups of cells differentiate to form tissues and organs At birth, most cells are already differentiated and simply grow and divide to adulthood Most animal cells lose totipotency; most plant cells do not Regulation of the Cell Cycle 
Cell‐cycle control systems and checkpoints Cell Cycle Clock 
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Cyclin‐dependant kinases (CDKs) – kinases present throughout the cell cycle but must be attached to a cyclin (protein whose concentration cycles) to be active. Kinases ‐ is a type of enzyme that transfers phosphate groups from high‐energy donor molecules, such as ATP, to specific target molecules (substrates) Triggers the cell’s passage from G2 to mitosis. Regulation of the Cell Cycle 
Cell‐cycle control systems and checkpoints Cancer ‐ Neoplasm 
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Cancer is uncontrolled, rapid cell division – mutation of the gene that regulates the cell cycle Normal cells grow, divide and stop dividing in response to signals from other cells Cancer cells grow faster and ignore these signals Normal cells tend to stick to similar cells while cancer cells do not. They tend to break away and settle in other parts of the body, a process called metastasis Cancer cells do not maintain their function but behave as unspecialized abnormal cells. They consume large amounts of resources to grow and divide but do not contribute to the functioning of the organism Mutations in these Cell Cycle regulatory genes cause cancer: 
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Proto‐Oncogenes – proteins that directly or indirectly promote the cell cycle (stimulatory pathway) Tumor suppressor genes – proteins that directly or indirectly inhibit the cell cycle (inhibitory pathway) Telomerase – inhibits the degradation of telomeres which signal cell senescence (biological aging) o Telomeres – DNA segments at ends of chromosome to protect strands; shorten after every cell division; when they get too small the cell stops dividing. Cancer 
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Often, segments of DNA are transposed from one location to another in the genome. Also, many mutagens are known to cause cancer. This suggests that changes to DNA can cause cancer Oncogenes ‐ Certain genes turn on cell division but are silent in their normal location. If they get transposed to another location they become active and cause cells to: o continue dividing o protect them from programmed cell death (apoptosis). o lose respect for normal tissue boundaries. o Have the ability to become established in diverse tissue environments o Most cells die after 20‐50 cell divisions but cancer cells are believed to be immortal.  E.g., a line of cancer cells called HeLa cells have been dividing in vitro since 1951 Aggressive, Invasive, Metastasis 
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These three malignant properties of cancers differentiate them from benign tumors, which are encapsulated and self‐limited in their growth and do not invade or metastasize (although some benign tumor types are capable of becoming malignant). Tumors require oxygen and nutrients, a process called Angiogenesis forms new blood vessels to the cancer cells. Cancer is usually classified according to the tissue from which the cancerous cells originate, as well as the normal cell type they most resemble. Most cancers can be treated and some cured, depending on the specific type, location, and stage of development. Cancer Treatment Once diagnosed, cancer is usually treated with a combination of surgery, chemotherapy and radiotherapy (not curative just relieves symptoms or prolongs or improves quality of life). Cloning 
Creating an organism that is an exact copy of a parent Three types of cloning technologies: 
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Recombinant DNA technology or DNA cloning Reproductive cloning Therapeutic cloning. Recombinant DNA technology or DNA cloning 
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Producing genetically identical organisms which carry a useful gene Construct a piece of DNA carrying a gene of interest and a gene for antibiotic resistance. 
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Insert this DNA into fetal cells. Grow the cells on a medium containing the antibiotic so that only the cells with the inserted DNA will survive. Insert the nuclei from surviving cells into enucleated egg cells. Implant the egg cells into the surrogate mother Clones are born which all carry the useful gene Reproductive Cloning 
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Dolly, the first mammal to be cloned from adult DNA Technology used to generate an animal that has the same nuclear DNA as another currently or previously existing animal. Genetic material is transferred from the nucleus of a donor adult cell to an egg whose nucleus, and thus its genetic material, has been removed. Fetal cow cells or cells from the ovary are harvested because they are still totipotent An electrical jolt triggers cell division The growing embryo is then implanted into the uterus of the surrogate mother The offspring is genetically identical to the original donor Therapeutic Cloning 
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“Embryo cloning" is the production of human embryos for use in research. The goal of this process is not to create cloned human beings, but rather to harvest stem cells that can be used to study human development and to treat disease. Stem cells are important to biomedical researchers because they can be used to generate virtually any type of specialized cell in the human body (totipotent). Stem cells are extracted from the egg after it has divided for 5 days (blastocyst). The extraction process destroys the embryo, which raises a variety of ethical concerns. Cloning Applications 
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Can produce cows which produce a useful protein in their milk Produce genetically identical organs for transplantation Repopulate endangered species Produce human tissue