Bio 1A Lect 4

Bio 1A Lect 4 - Doudna Office Hours Changed to T/W 9-10am...

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Unformatted text preview: Doudna Office Hours Changed to: T/W 9-10am 482 Stanley Hall Biology 1A Spring 2010 01/27/20 8:00am 1 Pimentel Dr. Doudna Lecture #4: Biological polymers •  Reading: Chapter 6, pp. 112‐124 •  Lecture outline: ‐Cytoskeleton ‐Extracellular matrix ‐Intercellular connecBons Network of fibers that gives the cell shape and allows it to move if needed The cytoskeleton is a network of fibers that organizes structures and ac?vi?es in the cell •  The cytoskeleton extends throughout the cytoplasm •  It organizes the cell’s structures and acBviBes, anchoring many organelles •  It is composed of three types of molecular structures: –  Microtubules –  Microfilaments –  Intermediate filaments Microtubule organized in a very intricate way, microscopy advances allow us to see this 0.25 µm Microfilaments Roles of the Cytoskeleton: Support, Mo?lity, and Regula?on •  The cytoskeleton helps to support the cell and maintain its shape •  It interacts with motor proteins to produce moBlity •  Inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton •  Recent evidence suggests that the cytoskeleton may help regulate biochemical acBviBes Moves the cell's fibers to allow the cell to change shape and movement. Fig. 6‐21 Membrane-enclosed sacs with cargo inside, moving along the microtubule ATP Motor proteins move using the energy from hydrolysis of ATP Vesicle Receptor for motor protein (a) Microtubule Motor protein (ATP powered) Vesicles Microtubule of cytoskeleton 0.25 µm (b) Components of the Cytoskeleton •  Three main types of fibers make up the cytoskeleton: –  Microtubules are the thickest of the three components of the cytoskeleton –  Microfilaments, also called acBn filaments, are the thinnest components –  Intermediate filaments are fibers with diameters in a middle range - all are composed of protein Table 6‐1 10 µm 10 µm 10 µm Column of tubulin dimers Ac?n subunit 25 nm 7 nm Kera?n proteins Fibrous subunit (kera?ns coiled together) 8–12 nm α β Tubulin dimer Microtubules •  Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns long •  FuncBons of microtubules: –  Shaping the cell –  Guiding movement of organelles –  SeparaBng chromosomes during cell division - microtubules are made from 2 subunits: alpha-tubulin and beta-t tubulin - DIRECTIONALITY: have a positive end and a negative end - positive end is very active - rapid addition or removal of tubulin - negative end is less active - slow addition or removal of tubulin Centrosomes and Centrioles •  In many cells, microtubules grow out from a centrosome near the nucleus •  The centrosome is a “microtubule‐organizing center” •  In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring IN ANIMAL CELLS Fig. 6‐22 Centrosome always perpendicular to one another Microtubule Centrioles 0.25 µm Longitudinal sec?on of Microtubules one centriole Cross sec?on of the other centriole allows cells to be motile Cilia and Flagella allows cells to move materials across their surface •  Microtubules control the beaBng of cilia and flagella, locomotor appendages of some cells •  Cilia and flagella share a common ultrastructure: –  A core of microtubules sheathed by the plasma membrane –  A basal body that anchors the cilium or flagellum –  A motor protein called dynein, which drives the bending movements of a cilium or flagellum secures to surface of the cell Fig. 6‐23 Sperm cells: the flagella resembles a motor, with a "crankshaft" that moves the sperm by creating force Direc?on of swimming (a) Mo?on of flagella 5 µm Direc?on of organism’s movement Epithelial Cells: the cilia resemble oars Power stroke Recovery stroke (b) Mo?on of cilia 15 µm Fig. 6‐25 Microtubule doublets ATP •  How dynein “walking” moves flagella and cilia: −  Dynein arms alternately grab, move, and release the outer microtubules –  Protein cross‐links limit sliding –  Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum cross-linking proteins hold the adjacent microtubules together, creating a bend Dynein protein (a) Effect of unrestrained dynein movement Cross‐linking proteins inside outer doublets ATP Anchorage in cell (b) Effect of cross‐linking proteins 1 2 3 dynein: spiral protein that has a fork; literally "walks" up the tubule (c) Wavelike mo?on Microvillus •  Plasma membrane •  Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of ac?n subunits The structural role of microfilaments is to bear tension, resisBng pulling forces within the cell They form a 3‐D network called the cortex just inside the plasma membrane to help support the cell’s shape Bundles of microfilaments make up the core of microvilli of intesBnal cells Microfilaments (ac?n filaments) •  •  Intermediate filaments 0.25 µm •  Microfilaments that funcBon in cellular moBlity contain the protein myosin in addiBon to acBn •  In muscle cells, thousands of acBn filaments are arranged parallel to one another •  Thicker filaments composed of myosin interdigitate with the thinner acBn fibers Fig, 6‐27a Muscle cell Ac?n filament Myosin filament Myosin arm (a) Myosin motors in muscle cell contrac?on Intermediate Filaments •  Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules •  They support cell shape and fix organelles in place •  Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes Tubulin is very dynamic - can shrink and grow quickly in the cell while flagella and cilia do not. Intermediate filaments are very permanent, sticking around in the cell even after the cell dies. Extracellular components help coordinate cellular acBviBes •  Most cells synthesize and secrete materials that are external to the plasma membrane •  These extracellular structures include: –  Cell walls of plants –  The extracellular matrix (ECM) of animal cells –  Intercellular juncBons Cell Walls of Plants •  The cell wall is an extracellular structure that disBnguishes plant cells from animal cells •  Prokaryotes, fungi, and some proBsts also have cell walls •  The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water •  Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein Sugar polymers: startch. Cellulose is very resistant to being broken down, even by enzymes. This brings up the issue about cellulose and biofuels •  Plant cell walls may have mulBple layers: bark •  Plasmodesmata are channels between adjacent plant cells –  Primary cell wall: relaBvely thin and flexible –  Middle lamella: thin layer between primary walls of adjacent cells –  Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata The Extracellular Matrix (ECM) of Animal Cells •  Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) •  The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronec?n •  ECM proteins bind to receptor proteins in the plasma membrane called integrins Proteins with long starch chains Connects the inside of the cell with the outside environment Proteins with sugars or sometimes long carbohydrates attached to them that act as identifiers. In cancer, the tumor cells express glycoproteins that are not typically there and this is used to identify tumor cells •  FuncBons of the ECM: –  Support –  Adhesion –  Movement –  RegulaBon Tumor cells seem to prefer stiffer extracellular matrix structure. Collagen EXTRACELLULAR FLUID Proteoglycan complex Polysaccharide molecule Carbo‐ hydrates Fibronec?n Core protein Integrins Plasma membrane Proteoglycan molecule Proteoglycan complex Micro‐ filaments CYTOPLASM Intercellular JuncBons •  Neighboring cells in Bssues, organs, or organ systems ocen adhere, interact, and communicate through direct physical contact •  Intercellular juncBons facilitate this contact •  There are several types of intercellular juncBons plant cells –  Plasmodesmata –  Tight juncBons –  Desmosomes –  Gap juncBons Plasmodesmata in Plant Cells •  Plasmodesmata are channels that perforate plant cell walls •  Through plasmodesmata, water and small solutes (and someBmes proteins and RNA) can pass from cell to cell Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes Tight seal between cells Tight junc?on Tight junc?ons prevent fluid from moving across a layer of cells Tight Junc:ons, Desmosomes, and Gap Junc:ons in Animal Cells 0.5 µm Tight junc?on Intermediate filaments Desmosome Desmosome Gap junc?ons 1 µm Space between cells Plasma membranes of adjacent cells Extracellular matrix Gap junc?on •  At ?ght junc?ons, membranes of neighboring cells are pressed together, prevenBng leakage of extracellular fluid •  Desmosomes (anchoring juncBons) fasten cells together into strong sheets •  Gap junc?ons (communicaBng juncBons) provide cytoplasmic channels between adjacent cells provide channels that allow molecules between cells (cell-cell communication) 0.1 µm The Cell: A Living Unit Greater Than the Sum of Its Parts Cells rely on the integraBon of structures and organelles in order to funcBon 5 µm •  For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinaBng components such as the cytoskeleton, lysosomes, and plasma membrane SUMMARY Cell Component Concept 6.3 The eukaryo?c cell’s gene?c instruc?ons are housed in the nucleus and carried out by the ribosomes Nucleus Structure Surrounded by nuclear envelope (double membrane) perforated by nuclear pores. The nuclear envelope is con?nuous with the endoplasmic re?culum (ER). Func?on Houses chromosomes, made of chroma?n (DNA, the gene?c material, and proteins); contains nucleoli, where ribosomal subunits are made. Pores regulate entry and exit of materials. (ER) Ribosome Two subunits made of ribo‐ somal RNA and proteins; can be free in cytosol or bound to ER Extensive network of membrane‐bound tubules and sacs; membrane separates lumen from cytosol; con?nuous with the nuclear envelope. Protein synthesis Concept 6.4 The endomembrane system regulates protein traffic and performs metabolic func?ons in the cell Endoplasmic re?culum (Nuclear envelope) Smooth ER: synthesis of lipids, metabolism of carbohy‐ drates, Ca2+ storage, detoxifica‐?on of drugs and poisons Rough ER: Aids in synthesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Modifica?on of proteins, carbo‐ hydrates on proteins, and phos‐ pholipids; synthesis of many polysaccharides; sor?ng of Golgi products, which are then released in vesicles. Golgi apparatus Stacks of flalened membranous sacs; has polarity (cis and trans faces) Lysosome Membranous sac of hydroly?c enzymes (in animal cells) Breakdown of ingested substances, cell macromolecules, and damaged organelles for recycling Diges?on, storage, waste disposal, water balance, cell growth, and protec?on Vacuole Large membrane‐bounded vesicle in plants Concept 6.5 Mitochondria and chloro‐ plasts change energy from one form to another Mitochondrion Bounded by double membrane; inner membrane has infoldings (cristae) Cellular respira?on Chloroplast Typically two membranes around fluid stroma, which contains membranous thylakoids stacked into grana (in plants) Specialized metabolic compartment bounded by a single membrane Photosynthesis Peroxisome Contains enzymes that transfer hydrogen to water, producing hydrogen peroxide (H2O2) as a by‐product, which is converted to water by other enzymes in the peroxisome SUMMARY Cell Component Concept 6.3 The eukaryo?c cell’s gene?c instruc?ons are housed in the nucleus and carried out by the ribosomes Nucleus Structure Surrounded by nuclear envelope (double membrane) perforated by nuclear pores. The nuclear envelope is con?nuous with the endoplasmic re?culum (ER). Func?on Houses chromosomes, made of chroma?n (DNA, the gene?c material, and proteins); contains nucleoli, where ribosomal subunits are made. Pores regulate entry and exit os materials. (ER) Ribosome Two subunits made of ribo‐ somal RNA and proteins; can be free in cytosol or bound to ER Protein synthesis SUMMARY Cell Component Concept 6.4 The endomembrane system regulates protein traffic and performs metabolic func?ons in the cell Endoplasmic re?culum Structure Func?on Smooth ER: synthesis of lipids, metabolism of carbohy‐ drates, Ca2+ storage, detoxifica‐ ?on of drugs and poisons Rough ER: Aids in sythesis of secretory and other proteins from bound ribosomes; adds carbohydrates to glycoproteins; produces new membrane Modifica?on of proteins, carbo‐ hydrates on proteins, and phos‐ pholipids; synthesis of many polysaccharides; sor?ng of Golgi products, which are then released in vesicles. Breakdown of ingested sub‐ stances cell macromolecules, and damaged organelles for recycling Diges?on, storage, waste disposal, water balance, cell growth, and protec?on Extensive network of membrane‐bound tubules and (Nuclear sacs; membrane separates envelope) lumen from cytosol; con?nuous with the nuclear envelope. Golgi apparatus Stacks of flalened membranous sacs; has polarity (cis and trans faces) Lysosome Membranous sac of hydroly?c enzymes (in animal cells) Large membrane‐bounded vesicle in plants Vacuole SUMMARY Cell Component Concept 6.5 Mitochondria and chloro‐ plasts change energy from one form to another Mitochondrion Structure Bounded by double membrane; inner membrane has infoldings (cristae) Func?on Cellular respira?on Chloroplast Typically two membranes around fluid stroma, which contains membranous thylakoids stacked into grana (in plants) Specialized metabolic compartment bounded by a single membrane Photosynthesis Peroxisome Contains enzymes that transfer hydrogen to water, producing hydrogen peroxide (H2O2) as a by‐product, which is converted to water by other enzymes in the peroxisome Based on lectures 3 & 4, you should now be able to: 1.  DisBnguish between the following pairs of terms: prokaryoBc and eukaryoBc cell; free and bound ribosomes; smooth and rough ER 2.  Describe the structure and funcBon of the components of the endomembrane system 3.  Briefly explain the role of mitochondria, chloroplasts, and peroxisomes 4.  Describe the funcBons of the cytoskeleton 5.  Compare the structure and funcBons of microtubules, microfilaments, and intermediate filaments 6.  Explain how the ultrastructure of cilia and flagella relate to their funcBons 7.  Describe the structure of a plant cell wall 8.  Describe the structure and roles of the extracellular matrix in animal cells 9.  Describe four different intercellular juncBons ...
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This note was uploaded on 02/26/2010 for the course BIO biology taught by Professor Meighan during the Spring '09 term at Berkeley.

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