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Transcript
Cell Structure and Function Chapter 4 Part 2 4.7 Visual Summary of Eukaryotic Cells CELL WALL Protects, structurally supports cell CYTOSKELETON Structurally supports, imparts shape to cell; moves cell and its components microtubules microfilaments intermediate filaments (not shown) MITOCHONDRION Energy powerhouse; produces many ATP by aerobic respiration PLASMODESMA Communication junction between adjoining cells PLASMA MEMBRANE Selectively controls the kinds and amounts of substances moving into and out of cell; helps maintain cytoplasmic volume, composition CHLOROPLAST CENTRAL VACUOLE Specializes in Increases cell surface area; photosynthesis stores metabolic wastes NUCLEUS Keeps DNA separated from cytoplasm; makes ribosome subunits; controls access to DNA nuclear envelope nucleolus DNA in nucleoplasm RIBOSOMES (attached to rough ER and free in cytoplasm) Sites of protein synthesis ROUGH ER Modifies proteins made by ribosomes attached to it SMOOTH ER Makes lipids, breaks down carbohydrates and fats, inactivates toxins GOLGI BODY Finishes, sorts, ships lipids, enzymes, and membrane and secreted proteins LYSOSOME-LIKE VESICLE Digests, recycles materials a Typical plant cell components. Fig. 4-15a, p. 63 4.7 Visual Summary of Eukaryotic Cells CYTOSKELETON Structurally supports, microtubules imparts shape microfilaments to cell; moves intermediate cell and its filaments components MITOCHONDRION Energy powerhouse; produces many ATP by aerobic respiration nuclear envelope nucleolus DNA in nucleoplasm NUCLEUS Keeps DNA separated from cytoplasm; makes ribosome subunits; controls access to DNA RIBOSOMES (attached to rough ER and free in cytoplasm) Sites of protein synthesis ROUGH ER Modifies proteins made by ribosomes attached to it CENTRIOLES Special centers that produce and organize microtubules SMOOTH ER Makes lipids, breaks down carbohydrates and fats, inactivates toxins PLASMA MEMBRANE Selectively controls the kinds and amounts of substances moving into and out of cell; helps maintain cytoplasmic volume, composition GOLGI BODY Finishes, sorts, ships lipids, enzymes, and membrane and secreted proteins LYSOSOME Digests, recycles materials Fig. 4-15b, p. 63 Animation: Common eukaryotic organelles 4.8 The Nucleus The nucleus keeps eukaryotic DNA away from potentially damaging reactions in the cytoplasm The nuclear envelope controls when DNA is accessed The Nuclear Envelope Nuclear envelope • Two lipid bilayers pressed together as a single membrane surrounding the nucleus • Outer bilayer is continuous with the ER • Nuclear pores allow certain substances to pass through the membrane The Nucleoplasm and Nucleolus Nucleoplasm • Viscous fluid inside the nuclear envelope, similar to cytoplasm Nucleolus • A dense region in the nucleus where subunits of ribosomes are assembled from proteins and RNA The Chromosomes Chromatin • All DNA and its associated proteins in the nucleus Chromosome • A single DNA molecule with its attached proteins • During cell division, chromosomes condense and become visible in micrographs • Human body cells have 46 chromosomes Chromosome Condensation one chromosome (one unduplicated DNA molecule) one chromosome (one duplicated DNA molecule, partially condensed) one chromosome (one duplicated DNA molecule, completely condensed) p. 65 4.9 The Endomembrane System Endomembrane system • A series of interacting organelles between the nucleus and the plasma membrane • Makes lipids, enzymes, and proteins for secretion or insertion into cell membranes • Other specialized cell functions The Endoplasmic Reticulum Endoplasmic reticulum (ER) • An extension of the nuclear envelope that forms a continuous, folded compartment Two kinds of endoplasmic reticulum • Rough ER (with ribosomes) folds polypeptides into their tertiary form • Smooth ER (no ribosomes) makes lipids, breaks down carbohydrates and lipids, detoxifies poisons Vesicles Vesicles • Small, membrane-enclosed saclike organelles that store or transport substances Peroxisomes • Vesicles containing enzymes that break down hydrogen peroxide, alcohol, and other toxins Vacuoles • Vesicles for waste disposal Golgi Bodies and Lysosomes Golgi body • A folded membrane containing enzymes that finish polypeptides and lipids delivered by the ER • Packages finished products in vesicles that carry them to the plasma membrane or to lysosomes Lysosomes • Vesicles containing enzymes that fuse with vacuoles and digest waste materials The Endomembrane System The Endomembrane System The Endomembrane System nucleus rough ER smooth ER Golgi body vesicles Fig. 4-18a, p. 66 A Nucleus Inside the nucleus, DNA instructions for making proteins are transcribed into RNA, which moves through nuclear pores into the cytoplasm. protein RNA C Vesicles B Rough ER Vesicles that bud from the Some of the RNA in rough ER carry some of the cytoplasm is the new proteins to Golgi translated into bodies. Other proteins polypeptide chains migrate through the by ribosomes interior of the rough ER, attached to the and end up in the smooth rough ER. The ER. chains enter the rough ER, where ribosome vesicle budding they are modified attached to ER from ER into final form. Fig. 4-18b, p. 66 protein in smooth ER D Smooth ER Some proteins from the rough ER are packaged into new vesicles and shipped to the Golgi. Others become enzymes of the ER, which assemble lipids or inactivate toxins. E Golgi body Proteins arriving in vesicles from the ER are modified into final form and sorted. New vesicles carry them to the plasma membrane or to lysosomes. F Plasma membrane Golgi vesicles fuse with the plasma membrane. Lipids and proteins of a vesicle’s membrane fuse with the plasma membrane, and the vesicle’s contents are released to the exterior of the cell. Fig. 4-18c, p. 67 Animation: The endomembrane system 4.10 Lysosome Malfunction When lysosomes do not work properly, some cellular materials are not properly recycled, which can have devastating results Different kinds of molecules are broken down by different lysosomal enzymes • One lysosomal enzyme breaks down gangliosides, a kind of lipid Tay Sachs Disease In Tay Sachs disease, a genetic mutation alters the lysosomal enzyme that breaks down gangliosides, which accumulate in nerve cells • Affected children usually die by age five 4.11 Other Organelles Eukaryotic cells make most of their ATP in mitochondria Plastids function in storage and photosynthesis in plants and some types of algae Mitochondria Mitochondrion • Eukaryotic organelle that makes the energy molecule ATP through aerobic respiration • Contains two membranes, forming inner and outer compartments; buildup of hydrogen ions in the outer compartment drives ATP synthesis • Has its own DNA and ribosomes • Resembles bacteria; may have evolved through endosymbiosis Mitochondrion outer membrane outer compartment inner compartment inner membrane 0.5 µm Fig. 4-20, p. 69 Plastids Plastids • Organelles that function in photosynthesis or storage in plants and algae; includes chromoplasts, amyloplasts, and chloroplasts Chloroplasts • Plastids specialized for photosynthesis • Resemble photosynthetic bacteria; may have evolved by endosymbiosis The Chloroplast two outer membranes stroma thylakoids (inner membrane system folded into flattened disks) Fig. 4-21, p. 69 Animation: Structure of a chloroplast The Central Vacuole Central vacuole • A plant organelle that occupies 50 to 90 percent of a cell’s interior • Stores amino acids, sugars, ions, wastes, toxins • Fluid pressure keeps plant cells firm 4.12 Cell Surface Specializations A wall or other protective covering often intervenes between a cell’s plasma membrane and the surroundings Eukaryotic Cell Walls Animal cells do not have walls, but plant cells and many protist and fungal cells do Primary cell wall • A thin, pliable wall formed by secretion of cellulose into the coating around young plant cells Secondary cell wall • A strong wall composed of lignin, formed in some plant stems and roots after maturity Plant Cell Walls Fig. 4-22a, p. 70 A Plant cell secretions form the middle lamella, a layer that cements adjoining cells together. middle lamella plasma membrane cytoplasm primary cell wall Fig. 4-22a, p. 70 Fig. 4-22b, p. 70 B In many plant tissues, cells also secrete materials that are deposited in layers on the inner surface of their primary wall. These layers strengthen the wall and maintain its shape. They remain after the cells die, and become part of pipelines that carry water through the plant. secondary cell wall (added in layers) primary cell wall pipeline made of abutting cell walls Fig. 4-22b, p. 70 Fig. 4-22c, p. 70 middle lamella C Plasmodesmata are channels across the cell walls and the plasma membranes of living cells that are pressed against one another in tissues. plasmodesma middle lamella Fig. 4-22c, p. 70 A Plant cell secretions form the middle lamella, a layer that cements adjoining cells together. middle lamella B In many plant tissues, cells also secrete materials that are deposited in layers on the inner surface of their primary wall. These layers strengthen the wall and maintain its shape. They remain after the cells die, and become part of pipelines that carry water through the plant. primary cell wall plasma membrane cytoplasm middle lamella C Plasmodesmata are channels across the cell walls and the plasma membranes of living cells that are pressed against one another in tissues. primary cell wall secondary cell wall (added in layers) plasmodesma middle lamella pipeline made of abutting cell walls Stepped Art Fig. 4-22, p. 70 Animation: Plant cell walls Plant Cuticle Cuticle • A waxy covering that protects exposed surfaces and limits water loss thick, waxy cuticle at leaf surface cell of leaf epidermis photosynthetic cell inside leaf Fig. 4-23, p. 71 Matrixes Between Animal Cells Extracellular matrix (ECM) • A nonliving, complex mixture of fibrous proteins and polysaccharides secreted by and surrounding cells; structure and function varies with the type of tissue • Example: Bone is mostly ECM, composed of collagen (fibrous protein) and hardened by mineral deposits ECM A bone cell surrounded by extracellular matrix Cell Junctions Cell junctions allow cells to interact with each other and the environment In plants, plasmodesmata extend through cell walls to connect the cytoplasm of two cells Animals have three types of cell junctions: tight junctions, adhering junctions, gap junctions Cell Junctions in Animal Tissues free surface of epithelial tissue different kinds of tight junctions gap junction basement membrane (extracellular matrix) adhering junction Fig. 4-25, p. 71 Animation: Animal cell junctions 4.6-4.12 Key Concepts: Eukaryotic Cells Cells of protists, plants, fungi, and animals are eukaryotic; they have a nucleus and other membrane-enclosed compartments They differ in internal parts and surface specializations 4.13 The Dynamic Cytoskeleton Eukaryotic cells have an extensive and dynamic internal framework called a cytoskeleton Cytoskeleton • An interconnected system of many protein filaments – some permanent, some temporary • Parts of the cytoskeleton reinforce, organize, and move cell structures, or even a whole cell Components of the Cytoskeleton Microtubules • Long, hollow cylinders made of tubulin • Form dynamic scaffolding for cell processes Microfilaments • Consist mainly of the globular protein actin • Make up the cell cortex Intermediate filaments • Maintain cell and tissue structures Components of the Cytoskeleton Fig. 4-26 (a-c), p. 72 Fig. 4-26a, p. 72 tubulin subunit 25 nm Microtubule Fig. 4-26a, p. 72 Fig. 4-26b, p. 72 actin subunit 6–7 nm Microfilament Fig. 4-26b, p. 72 one polypeptide chain Intermediate filament Fig. 4-26c, p. 72 Fig. 4-26d, p. 72 tubulin subunit 25 nm Microtubule actin subunit one polypeptide chain Intermediate filament 6–7 nm Microfilament Stepped Art Fig. 4-26, p. 72 Motor Proteins Motor proteins • Accessory proteins that move molecules through cells on tracks of microtubules and microfilaments • Energized by ATP • Example: kinesins Motor Proteins: Kinesin Animation: Motor proteins Cilia, Flagella, and False Feet Eukaryotic flagella and cilia • Whiplike structures formed from microtubules organized into 9 + 2 arrays • Grow from a centriole which remains in the cytoplasm as a basal body Psueudopods • “False feet” used by amoebas and other eukaryotic cells to move or engulf prey Moving Cells Flagellum of the human sperm, and pseudopods of a predatory amoeba Fig. 4-28a, p. 73 Fig. 4-28b, p. 73 Eukaryotic Flagella and Cilia Fig. 4-29a, p. 73 protein spokes pair of microtubules in a central sheath pair of microtubules plasma membrane dynein arms A Sketch and micrograph of one eukaryotic flagellum, cross-section. Like a cilium, it contains a 9+2 array: a ring of nine pairs of microtubules plus one pair at its core. Stabilizing spokes and linking elements that connect to the microtubules keep them aligned in this radial pattern. Fig. 4-29a, p. 73 Fig. 4-29b, p. 73 B Projecting from each pair of microtubules in the outer ring are “arms” of dynein, a motor protein that has ATPase activity. Phosphategroup transfers from ATP cause the dynein arms to repeatedly bind the adjacent pair of microtubules, bend, and then disengage. The dynein arms “walk” along the microtubules. Their motion causes adjacent microtubule pairs to slide past one another basal body, a microtubule organizing center that gives rise to the 9+2 array and then remains beneath it, inside the cytoplasm Fig. 4-29b, p. 73 Fig. 4-29c, p. 73 C Short, sliding strokes occur in a coordinated sequence around the ring, down the length of each microtubule pair. The flagellum bends as the array inside bends: Fig. 4-29c, p. 73 Animation: Flagella structure 4.13 Key Concepts: A Look at the Cytoskeleton Diverse protein filaments reinforce a cell’s shape and keep its parts organized As some filaments lengthen and shorten, they move cell structures or the whole cell Summary: Components of Prokaryotic and Eukaryotic Cells Animation: Nuclear envelope Video: E. coli in food Video: Cilia and flagella protozoans