PowerPoint Presentation Chapter 9

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Cellular Reproduction
Chapter 9 Principles of Biology
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Why Cells Divide

• Cell size is limited
• Cells cannot keep growing indefinitely
• Replacement of damaged cells
• Growth - embryo
• Asexual reproduction
• Single celled life forms
• Plant cuttings
• Sexual reproduction - meiosis next chapter

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Binary Fission

• Division of prokaryotic cell
• No nucleus
• Bacteria and Archea
• One large circular chromosome
• Chromosome is replicated (copied)
• Both two chromosomes attached to plasma membrane
• New membrane separates chromosomes
• Cell size doubling promotes division

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Cell cycle

• Interphase 90 of dividing cells
• Makes proteins
• Grows
• Copies organelles
• Also copies chromosomes
• G1 phase, S phase, G2 phase
• S- synthesis of DNA
• Sister chromatids form
• Mitotic phase
• Mitosis - nuclear division
• Cytokinesis - division of cytoplasm

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Eukaryotic chromosomes

• Chr. Become visible before division
• Long chromatin strands coil
• How many chromosomes do humans have?
• 46 or 23 pairs
• Each new cell must have a complete set of chr.
• Chr. Must be copied

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Cell Cycle and Mitosis

• Before a cell divides it must copy DNA
• Genes are found on chromosomes
• Chroma - colored body
• Soma - body
• First noticed when staining cells
• To look at under microscope
• Only visible sometimes
• Chromatin - combo of DNA protein

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One chromosome

• Unduplicated (unreplicated)
• Replicated chromosome
• Consists of 2 sister chromatids
• Exact copies of each other
• Connected by a centromere
• Cell division separates chromatids
• Each new cell gets one copy of each chr

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Mitosis

• Prophase
• Chromosomes coil -can see them now
• Nuclear membrane and nucleolus break down
• Prometaphase
• Mitotic spindle forms
• Microtubules radiate out from centrioles
• Cellular poles form
• Microtubules capture chr at centromere
• Each chr now connected to both poles
• Microtubules begin moving chr

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Mitosis

• Metaphase (middle)
• Chromosomes lined up at equator
• Microtubules attach chromatids to opposite poles
• Anaphase (apart)
• Sister chromatids separate
• Chromatids now chromosome
• Microtublues pull chr to poles
• Other microtubules elongate cell

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• Teleophase reverses prophase events
• Begins when chr reach poles
• Nuclear envelopes form
• Chromosomes stretch out
• Nucleoli form
• Spindle breaks down
• Cytokinesis
• Division of cellular contents
• Cytoplasm
• Organelles
• Animal cells form cleavage furrow
• Plants form cell plate

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Cell cycle enzymes

• Moving from one phase to another is promoted by
  enzymes
• Kinase takes a phosphate from ATP and adds it to
  a protein molecule
• Used to kick start cellular processes
• Cyclin activate kinases
• S-cyclin (S synthesis) joins with S-kinase
• Stimulates DNA synthesis -S phase
• M-cyclin (M mitosis) joins with M-kinase
• Mitosis begins

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Cancer

• Cell cycle control system
• Enzymes in cell control when and where cells
  divide
• Malfunction in system means cells divide at
  inappropriate times and places
• Benign tumor - abnormal mass of essentially
  normal cells
• Stay at original site, dont move
• Cancer uncontrolled cell division

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Cancer

• Problem not only uncontrolled division
• Metastisis
• Cancer cells can move to other sites
• New tumor at that site
• Three treatments
• Surgery to remove tumor
• Radiation
• Chemotherapy
• Last two aimed at controlling division

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Cancer treatments

• Radiation
• Disrupts cell division
• Most actively dividing cells are tumor
• Can damage normal cells- ovaries / testes
• Chemotherapy
• Some disrupt cell division
• Taxol freezes spindle
• Vinblastine prevents spindle formation
• Cancer cells immortal in cell culture
• Normal cells stop growing after 50 cultures

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p53 gene

• Tumors often due to a mutation in p53 gene so it
  doesnt work
• Normal gene controls division
• By producing a protein that binds to cyclins so
  they cant bind to kinase
• So division is controlled (stopped)
• Occurs when DNA becomes damaged
• Protein promotes DNA repair
• If repair is not possible cell is destroyed
• Apoptosis programmed cell death

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Future treatments

• Tumor cells contain survivin
• Which blocks apoptosis
• Control of this process could lead to new
  treatments for diseases
• Parkinsons and stroke lead to cell death at
  inappropriate times
• Maybe we could turn off apoptosis
• Cancer prevents apoptosis when it should occur
• Maybe we could turn apoptosis on

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