Membranes and Cells Fall 2011

Membranes and Cells Fall 2011 - Biological Membranes...

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Unformatted text preview: Biological Membranes Biological Diffusion Net movement of substance down its Net concentration gradient concentration – from region of greater concentration – to region of lower concentration Does not use direct metabolic energy 1. When lump of sugar is dropped into beaker of pure water, sugar molecules begin to dissolve and diffuse through water. 2. Sugar molecules continue to dissolve and diffuse through water. 3. Eventually sugar molecules become distributed randomly throughout water. What are the components of cell membranes? membranes? 1. Phospholipids 2. Proteins 3. Polysaccharides 4. All of the above 5. None of the above e 0 ab ov ab id e s ov e 0 e ll o of th e ft he ch ar N on ac ly s Po 0 A s ro te i P lip id sp ho ho P 0 ns 0 Phospholipid Molecules Molecules Amphipathic: Amphipathic – both hydrophobic and hydrophilic regions – hydrophilic heads at 2 surfaces of bilayer at bilayer – hydrophobic fatty acid chains interior (b) Detergent in water. Detergent molecules are roughly cone-shaped amphipathic molecules that associate in water as spherical structures. Phospholipid Molecules Molecules Amphipathic: Amphipathic – both hydrophobic and hydrophilic regions – hydrophilic heads at 2 surfaces of bilayer at bilayer – hydrophobic fatty acid chains interior Hydrophilic heads Hydrophobic tails (a) Phospholipids in water. Phospholipids associate as bilayers in water because they are roughly cylindrical amphipathic molecules. The hydrophobic fatty acid chains are not exposed to water, whereas the hydrophilic phospholipid heads are in contact with water. Which of the following is NOT a Which function of plasma membranes? function 0 0 0 in te rio m ro pa R ... eg rt m ul en at e ts w ... C ha om tg m oe un s ic i.. at A . e ll of w ith th e ot ab ... ov e ar e f.. . co th e rm 5. 0 ra te 4. Fo 3. pa 2. Separate the interior of Separate the cell from the exterior the Form compartments Form inside the cell inside Regulate what goes Regulate into/out of the cell into/out Communicate with other Communicate cells cells All of the above are All functions of plasma membranes membranes Se 1. 0 Plasma Membrane Plasma 1. Physically separates – interior of cell from external environment 2. Receives information – about changes in environment 3. Regulates 3. – passage of materials in and out of cell Plasma Membrane 4. Communicates – with other cells 5. Forms compartments – to allow separate functions 6. Participates in biochemical reactions KEY CONCEPTS KEY Biological membranes are selectively Biological permeable membranes that help maintain homeostasis in the cell homeostasis Which of the following terms/ Which phrases is used to describe the basic model of plasma membranes? basic 1. Homeostatic 2. Isotonic 3. Fluid mosaic 4. None of these 0 th es e of e on N ui d m os ot on ic Is 0 ai c 0 Fl H om eo s ta tic 0 Fluid Mosaic Model Fluid Membranes – fluid phospholipid bilayer fluid phospholipid – variety of proteins embedded Phospolipid Bilayer Cell Membrane Lipid Bilayer Bilayer Flexible and self-sealing Fuses with other membranes – allows transport of materials within cell Forms vesicles – bud from one cell membrane – fuse with another membrane Hydrophilic region of protein Hydrophobic region of protein Phospholipid bilayer Peripheral protein Integral (transmembrane) protein (b) Fluid mosaic model. According to this model, a cell membrane is a fluid lipid bilayer with a constantly changing “mosaic pattern“ of associated proteins. Membrane Proteins Membrane Integral membrane proteins – embedded in bilayer Transmembrane proteins – extend completely through membrane Peripheral membrane proteins – at surface of bilayer – bound to exposed integral proteins The Plasma Membrane Which of the following is a function of membrane proteins? of 1. Transport materials 2. Act as receptors for Act 0 ot S tr uc t rs R ec re c 0 ... he rc ur el ls al ly lin k A ce ll lls of th e ab ov e 0 fo r s 0 og ni ze at er ia l m ep to or t sp as ct 5. 0 Tr an 4. A 3. extracellular molecules molecules Recognize other Recognize cells cells Structurally link Structurally cells cells All of the above KEY CONCEPTS According to the fluid mosaic model, cell According membranes consist of a fluid bilayer composed of phospholipids in which a variety of proteins are embedded variety Selectively Permeable Membranes Membranes Allow passage of some substances but not Allow others others Controls volume and internal composition Controls of cell’s ions and molecules of Osmosis A type of diffusion H2O molecules pass through a selectively molecules permeable membrane permeable – from higher effective H2O concentration – to lower effective H2O concentration concentration Osmosis Osmosis Osmotic Pressure Determined by concentration of solutes Determined Cells regulate internal osmotic pressure osmotic – to prevent shrinking or bursting Tonicity Tonicity Isotonic solutions Isotonic solutions – equal solute concentration Hypertonic solution – in solute concentration > the cell’s – cell loses water to surroundings Hypotonic solution – in solute concentration < the cell’s – water enters, cells swell Osmotic Osmotic Pressure Pressure Plant Cells Plant Plasmolysis – in hypertonic solution, water moves out – plasma membrane splits from cell wall plasma Turgor pressure Turgor – in hypotonic solution, water moves in – cells swell, build pressure against cell walls Plasma membrane Nucleus Cytoplasm Plasma membrane Vacuole Vacuolar membrane (tonoplast) Vacuole Do you feel prepared for exam #1? 1. Yes 2. No 70% o N Y es 30% BETA BETA BETA Biological Sciences Honors Fraternity Interested in biology, networking, academic advising, research opportunities, community service and prehealth professions? apply to BETA BETA BETA today! Interest Meetings: Wednesday, September 21, 2011 at 6pm, 106 LSC Monday September 26, 2011 at 6pm, 106 LSC Rush Events: Kaplan Presentation- Thursday, September 22, 2011 at 630pm, 106 LSC Mixer- Monday September 26, 2011 at 7pm, 106 LSC email TRI BETA at: with any other questions why be an alpha when you can tri-beta? KEY CONCEPTS KEY Diffusion is passive – does not require the Diffusion does cell to expend metabolic energy cell Active transport requires direct Active expenditure of energy expenditure Simple vs Facilitated Simple diffusion – molecules or ions move directly through the molecules membrane membrane – down their concentration gradient Facilitated diffusion – specific transport proteins move solutes specific across a membrane across – down their concentration gradient Facilitated Diffusion Facilitated Does facilitated diffusion cost the Does cell energy? cell 1. Yes 199 2. No o N Y es 143 Active Transport Active Cell uses metabolic energy – to move ions or molecules – across a membrane – against a concentration gradient Example: sodium–potassium pump Example: sodium – uses ATP to pump sodium ions out and uses potassium ions in potassium Lower Lower Potassium concentration gradient Outside cell Sodium concentration gradient Higher Cytosol Higher (a) The sodium–potassium pump is a carrier protein that requires energy from ATP. In each complete pumping cycle, the energy of one molecule of ATP is used to export three sodium ions (Na+) and import two potassium ions (K+). 2. Phosphate group is transferred from ATP to transport protein. 3. Phosphorylation causes carrier protein to change shape, releasing 3 Na+ outside cell. 1. Three Na+ bind to transport protein. 4. Two K+ bind to transport protein. 6. Phosphate release causes carrier protein to return to its original shape. Two K+ ions are released inside cell. 5. Phosphate is released. Cotransport Co-transport… Co 1. Never costs the cell Never th e co Compare transport mechanisms of Compare exocytosis and endocytosis exocytosis and endocytosis on N nd ir ti ig h M Bulk Transport e ec of tly st s co el y ab ov e st t.. .. 22 th e. ll ... ce e th ia t co st s Im m ed er 4. 34 ev 3. 149 147 N 2. energy energy Immediately costs Immediately the cell energy at the point of cothe transport Might indirectly cost Might the cell energy the None of the above Exocytosis Exocytosis Materials exit cell Materials exit Membrane surface Membrane area increases increases Endocytosis Materials enter cell Materials enter Membrane surface area decreases Membrane decreases 3 types of endocytosis – phagocytosis – pinocytosis – receptor-mediated endocytosis Phagocytosis Large particles enter cell enter Pinocytosis Dissolved materials enter cell Dissolved enter Receptor-mediated Endocytosis Plasma membrane Cytosol 2 1 LDL attaches to specific receptors in coated pits on plasma membrane. 2 Endocytosis results in formation of a coated vesicle in cytosol. Seconds later coat is removed. 3 Uncoated vesicle fuses with endosome. 4 Receptors are returned to plasma membrane and recycled. 5 Vesicle containing LDL particles fuses with a lysosome, forming a secondary lysosome. Hydrolytic enzymes then digest cholesterol from LDL particles for use by cell. Coated pit 1 LDL particle LDL receptor Clathrin Uncoated vesicle Clathrin recycled Endosome 3 Primary lysosome Endosome 5 Secondary lysosome Free cholesterol 4 (a) Uptake of low-density lipoprotein (LDL) particles, which transport cholesterol in the blood. 0.25 µm (b) This series of TEMs shows the formation of a coated vesicle from a coated pit. A (Quick) Tour of Cells Cell Theory (1) Cells are basic units of organization and function in all living organisms (2) All cells come from other cells All living cells have evolved from a common ancestor Which of the following is largest? 1. Carbon atom 2. An average sized av e n A ru s vi A eu si ze d e ra g ra g av e n A k. .. ct ... .. si ze d e e ba pr o. at om n si ze d ar bo C er ag n A Biological Size 12% 11% 11% 6% av protein macromolecule 3. An average sized bacterium 4. An average sized eukaryotic cell 5. A virus 60% How do the general characteristics of prokaryotic and eukaryotic cells differ? How are plant and animal cells different? Do bacteria have organelles? 1. Yes 2. No 61% o N Y es 39% Prokaryotes Prokaryotic cells – Cytoplasm – No internal membrane organization – nuclear area (not nucleus) – cell wall – ribosomes – flagella Prokaryotes Eukaryotes Eukaryotic cells – membrane-enclosed nucleus – cytoplasm contains membrane-bound organelles – cytosol (fluid component) Animal Cells Plant Cells Plant cells – rigid cell walls – plastids – large vacuoles – no centrioles Plant Cells The Nucleus Control center of cell – genetic information coded in DNA Nuclear envelope – double membrane Nuclear pores – communicate with cytoplasm Nuclear Structures Chromatin – DNA and protein Chromosomes – DNA condensed for cell division Nucleolus – ribosomal RNA synthesis – ribosome assembly The Nucleus Endoplasmic Reticulum (ER) Network of folded membranes – in cytosol Smooth ER – lipid synthesis – calcium ion storage – detoxifying enzymes Rough ER – ribosomes on outer surface – assembles proteins ER The Golgi Complex Processes proteins synthesized by ER Manufactures lysosomes Cisternae – stacks of flattened membranous sacs Protein Production KEY CONCEPTS Proteins are – synthesized on ribosomes – processed in the endoplasmic reticulum – processed by the Golgi complex – transported by vesicles Other Organelles Lysosomes – enzymes break down structures Vacuoles – store materials in plant cells Peroxisomes – produce and degrade hydrogen peroxide (catalase) Mitochondria Site of aerobic respiration Double membrane – inner membrane folded (cristae) – matrix (cristae and inner compartment) Important in apoptosis – programmed cell death Mitochondria Plastids Plastids – organelles that produce and store food – in cells of plants and algae Chloroplasts – plastids that carry out photosynthesis Chloroplasts The Cytoskeleton Microtubules – hollow tubulin cylinders Microfilaments – actin filaments – important in cell movement Intermediate filaments – strengthen cytoskeleton – stabilize cell shape 50 µm (b) Fluorescent LM showing microtubules in green. A microtubule-organizing center (pink dot) is visible beside or over most of the cell nuclei (blue). Fig. 4-22b, p. 98 100 µm (b) Intermediate filaments are stained green in this human cell isolated from a tissue culture. Fig. 4-27b, p. 101 100 µm (b) Many bundles of microfilaments (green) are evident in this fluorescent LM of fibroblasts, cells found in connective tissue. Fig. 4-26b, p. 101 Cytoskeleton KEY CONCEPTS The cytoskeleton is a dynamic internal framework that functions in various types of cell movement Cilia and Flagella Cilia and flagella – thin, movable structures – project from cell surface – function in movement Cilia are short, flagella are long Fig. 4-25, p. 100 ...
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This note was uploaded on 10/06/2011 for the course BIOLOGY 121 taught by Professor Staff during the Fall '11 term at Syracuse.

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