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Lesson 4: Cell Composition February 4, 2015

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2 Cells Cells were discovered in 1665 by Robert Hooke Early studies of cells were conducted by Mathias Schleiden (1838) Theodor Schwann (1839) Schleiden and Schwann proposed the Cell Theory

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3 Cell Theory 1.All organisms are composed of cells 2.Cells are the smallest living things 3.Cells arise only from pre-existing cells All cells today represent a continuous line of descent from the first living cells

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4 Cell Size is Limited Cells rely on material being transported through their membranes Rate of diffusion affected by Surface area available Temperature Concentration gradient Distance

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6 Similarities Between All Cells 1.Nucleic Material Nucleiod region or nucleus 2.Cytoplasm Semifluid matrix of organelles and cytosol 3.Ribosomes Synthesize proteins 4.Plasma membrane Phospholipid bilayer

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7 Prokaryotic Cells Simplest organisms Lack organelles DNA is present in the nucleoid region Cell wall Surrounds plasma membrane Two domains of prokaryotes Archaea (lacks peptidoglycan) Bacteria (contains peptidoglycan)

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Bacterial Cell Walls Most bacterial cells are encased by a strong cell wall Composed of peptidoglycan Cell walls of plants, fungi, and most protists different Protect the cell, maintain its shape, and prevent excessive uptake or loss of water Susceptibility of bacteria to antibiotics often depends on the structure of their cell walls Archaea lack peptidoglycan!!!! 9

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10 Eukaryotic Cells More complex than prokaryotic cells Hallmark is the presence of organelles Possess a cytoskeleton for support and to maintain cellular structure

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11 ANIMAL CELL

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12 PLANT CELL

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13 Nucleus Storage are of genetic information Nucleolus region where RNA synthesis takes place Nuclear envelope 2 phospholipid bilayers Nuclear pores regulates passage of material In Eukaryotes, the DNA is divided into multiple linear chromosomes Chromatinchromosomes bound by proteins 23 pairs of chromosomes in Humans

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14 NUCLEUS

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Ribosomes Place where protein synthesis occurs Found in all cells Comprised of a ribosomal RNA (rRNA) and proteins Protein synthesis also requires messenger RNA (mRNA) and transfer RNA (tRNA) Ribosomes may be free in cytoplasm or associated with endoplasmic reticulum 15

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16 Endoplasmic Reticulum Rough endoplasmic reticulum (RER) Attachment of ribosomes to the membrane gives a rough appearance Synthesis of proteins to be secreted, sent to lysosomes or plasma membrane Smooth endoplasmic reticulum (SER) Relatively few bound ribosomes Functions in fatty-acid synthesis, storage of Ca 2+, detoxification of the cell Ratio of RER to SER depends on cells function

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18 Golgi Apparatus Flattened stacks of interconnected membranes (Golgi bodies) Functions in packaging, modification, and distribution of proteins (transport to membrane or exocytosis of proteins) Cis and Trans faces Vesicles transport molecules to destination Transport vesicles vs. secretory vesicles

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21 Lysosomes Membrane-bounded digestive vesicles Arise from Golgi apparatus Enzymes catalyze breakdown of macromolecules (acidic environment) Proteases, nucleases, carbohydrases, lipases Destroy cells or foreign matter that the cell has engulfed by phagocytosis or for recycling organelles

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Microbodies Variety of enzyme- bearing, membrane- enclosed vesicles Peroxisomes Contain enzymes involved in the oxidation of fatty acids H 2 O 2 produced as by- product rendered harmless by catalase 23

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24 Vacuoles Membrane-bounded structures in PLANTS Various functions depending on the cell type There are different types of vacuoles: Central vacuoles in plant cells stores water, food, and waste Contractile vacuole of some protists function in osmoregulation

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26 Mitochondria Found in all Eukaryotic cells Bound by membranes Outer membrane Intermembrane space Inner membrane has cristae Matrix On the surface of the inner membrane, and also embedded within it, are proteins that carry out oxidative metabolism Contain their own DNA

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28 Chloroplasts Organelles present in cells of plants Contain chlorophyll (pigment used in photosynthesis) Surrounded by 2 membranes Thylakoids are membranous sacs within the inner membrane Grana are stacks of thylakoids Contain their own DNA

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30 Endosymbiosis Leads to Organelles Proposes that some of todays eukaryotic organelles evolved by a symbiosis arising between two cells that were each free-living One cell, a prokaryote, was engulfed by and became part of another cell, which was the precursor of modern eukaryotes Mitochondria and chloroplasts

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32 Cytoskeleton Network of protein fibers found in all eukaryotic cells Supports the shape of the cell Keeps organelles in fixed locations Transportation of molecules within the cell Dynamic system constantly forming and disassembling

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33 Three Types of Cytoskeleton Microfilaments (actin filaments) Two protein chains loosely twined together Movements like contraction, crawling, pinching Microtubules Largest of the cytoskeletal elements Dimers of - and -tubulin subunits Facilitate movement of cell and materials within cell Intermediate Filaments Between the size of actin filaments and microtubules Very stable usually not broken down

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Centrosomes Region surrounding centrioles in almost all animal cells Microtubule-organizing center (found in plants) Can nucleate the assembly of microtubules Animal cells and most protists have centrioles pair of organelles Plants and fungi lack centrioles!!!! 35

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Eukaryotic cell walls Plants, fungi, and many protists Different from prokaryote Plants and protists cellulose Fungi chitin Plants primary and secondary cell walls 36

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37 Extracellular matrix (ECM) Animal cells secrete an elaborate mixture of glycoproteins into the space around them Collagen, laminins, fibronectin, elastins Form a protective layer over the cell surface Integrins link ECM to cells cytoskeleton Influences cell behavior

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