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Chapter 5 The Working Cell
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Chapter 5: Concepts Energy : Kinetic, Potential, chemical and Entropy
ATP: How we get energy out of it Enzymes: Activation energy, importance of shape Membrane function: Active and Passive transport plus cell signaling Osmosis Exocytosis and Endocytosis
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Biology and Society: Natural Nanotechnology
Cells control their chemical environment using Energy Enzymes The plasma membrane Cell-based nanotechnology may be used to power microscopic robots. © 2010 Pearson Education, Inc. All living processes depend on energy which is supplied by the cell through a process called glycolysis. The energy is released by the breakdown of food molecules using enzymes. In this chapter we will study how a cell uses energy, enzymes and PM to carry out the work of controlling its internal chemical environment.
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SOME BASIC ENERGY CONCEPT
Energy makes the world go round . All organisms require energy to stay alive Energy is defined as the capacity to perform work. Whenever something moves against an opposing force, work is performed Some forms of energy are used to perform work. Energy is the ability to rearrange a collection of matter. Energy is defined as the capacity to perform work and it makes the world go around. Work is performed whenever an object is moved against an opposing force. Work must be performed when you climb up stairs to overcome the force of gravity. Potential energy is energy that an object has because of its location or structure such as water stored in dam or in a compressed spring.
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Conservation of Energy
Energy primarily come into two different types One form is Kinetic Energy, that a body possesses by virtue of being in motion. Where as Potential (stored energy) is the opposite, an energy that an object has because of its location or structure. Machines and organisms can transform kinetic energy to potential energy and vice versa, in such transformations total energy is conserved. The conservation of energy (first law of thermodynamic) states that it is not possible to destroy or create energy. it can only be converted from one form to another. For example, the chemical energy (=potential energy) in the covalent bonds of gasoline molecules is converted to kinetic energy to move the car Energy is defined as the capacity to perform work and it makes the world go around. Work is performed whenever an object is moved against an opposing force. Work must be performed when you climb up stairs to overcome the force of gravity. Potential energy is energy that an object has because of its location or structure such as water stored in dam or in a compressed spring.
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Potential Vs. Kinetic Energy Diagram:
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Energy conversions during a dive
In living systems, energy is converted in an energy cycle from kinetic to potential energy and back Climbing the steps converts Kinetic energy of muscle movement to potential energy. On the platform, the diver has more potential energy. Diving converts potential energy to kinetic energy. In the water, the diver has less Figure 5.1Energy conversions during a dive
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Heat Every energy conversion releases some randomized energy in the form of heat. Heat is a a type of kinetic energy contained in the random motion of atoms and molecules a product of all energy conversions If energy is not destroyed where it has gone when the diver hits the water? It has been converted to heat in the air and then in water which is produced by the friction between the body and its surroundings.
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Entropy Scientists use the term entropy as a measure of disorder, or randomness in a system. All energy conversions increase the entropy of the universe This is because some energy is always “lost” as heat No energy conversion is ever perfectly 100% efficient Example: food web trophic levels This is the second law of Thermodynamic If energy is not destroyed where it has gone when the diver hits the water? It has been converted to heat in the air and then in water which is produced by the friction between the body and its surroundings.
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Chemical Energy Molecules store varying amounts of potential energy in the arrangement of their atoms. Organic compounds are relatively rich in such chemical energy Is found in food, gasoline and other fuels Living cells and automobile engines use the same basic process to make chemical energy do work They take in the energy rich molecules, then process the energy, and that gives off heat. Then the waste products are removed Cellular respiration is the energy-releasing chemical breakdown of fuel molecules that provides energy for cells to do work Humans convert about 40% of the energy in food to useful work, such as the contraction of muscles Carbs, fats and gasoline have structures that makes them especially rich in chemical energy. Whether it is a living cells or automobile engines, they use the same basic process to make chemical energy do work. They breakdown the organic fuel molecules thereby releasing the energy for cells to do work. About 60% of energy released generates the body heat.
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Energy conversions in a car and a cell
Fuel rich in chemical energy Energy conversion Waste products poor in chemical Gasoline Oxygen Carbon dioxide Water Energy conversion in a car Energy for cellular work Energy conversion in a cell Heat Food Combustion Cellular respiration Kinetic energy of movement ATP Figure 5.2 Energy conversions in a car and a cell In both car and a cell, the chemical energy of organic fuel is harvested using oxygen. This chemical breakdown releases energy stored in the fuel molecules and produces CO2 and H2O. The released energy can be used to perform work.
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Food Calories A calorie is a unit of energy
it is simply the amount of energy that can raise the temperature of 1 gram of water by 1 degree Celsius.
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Food Calories Food Calories are kilocalories, equal to 1,000 calories.
The energy of calories in food is burned off by many activities. (a) Food Calories (kilocalories) in various foods (b) Food Calories (kilocalories) we burn in various activities Cheeseburger Spaghetti with sauce (1 cup) Pizza with pepperoni (1 slice) Peanuts (1 ounce) Apple Bean burrito Fried chicken (drumstick) Garden salad (2 cups) Popcorn (plain, 1 cup) Broccoli (1 cup) Baked potato (plain, with skin) Food Calories Food 295 241 220 193 181 166 81 56 189 31 25 Activity Food Calories consumed per hour by a 150-pound person* 979 510 490 408 204 73 61 245 28 Running (7min/mi) Sitting (writing) Driving a car Playing the piano Dancing (slow) Walking (3 mph) Bicycling (10 mph) Swimming (2 mph) Dancing (fast) *Not including energy necessary for basic functions, such as breathing and heartbeat Figure 5.3 Some caloric accounting
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ATP AND CELLULAR WORK Releases it later as needed
Chemical energy of organic molecules is released by the breakdown of organic molecules during cellular respiration and used to generate molecules of ATP ATP acts like an energy shuttle stores energy obtained from food Releases it later as needed
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Blast Animation: Structure of ATP
The Structure of ATP ATP (adenosine triphosphate) Consists of adenosine plus a tail of three phosphate groups ATP is broken down to ADP and a phosphate group, releasing energy Triphosphate Diphosphate Adenosine Energy ATP ADP P Phosphate (transferred to another molecule) Blast Animation: Structure of ATP Figure 5.4 ATP power
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Phosphate Transfer ATP ADP P X Y (a) Motor protein performing mechanical work (b) Transport protein performing transport work (c) Chemical reactants performing chemical work Solute Solute transported Protein moved Product made Reactants Transport protein Motor ATP can energizes other molecules by transferring phosphate groups. This energy helps cells perform Mechanical work Transport work Chemical work Figure 5.5 How ATP drives cellular work Each type of work shown here is powered when enzymes transfer phosphate from ATP to a recipient molecule. Chemical work: the transport of ions prepares the brain cells to transmit signals to muscles and other tissues. All these types of work occur when target molecules accept a phosphate group from ATP.
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The ATP Cycle Cellular work spends ATP.
ATP is recycled from ADP and a phosphate group through cellular respiration. A working muscle cell spends and recycles about 10 million ATP molecules per second. Cellular respiration: chemical energy harvested from fuel molecules Energy for cellular work ATP ADP P Figure 5.6 The ATP cycle
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Enzymes and Activation Energy
Metabolism is defined as the total of all chemical reactions in an organism. Most metabolic reactions require the assistance of enzymes, proteins that speed up chemical reactions. Activation energy: A chemical reaction begins with chemical bonds in the reactant molecules being broken. This process requires that molecules absorb energy from their surroundings; this is called activation energy, because it activates the reactants & triggers the chemical reaction Activation energy is the energy needed to cause a reaction to occur, it activates the reactants and triggers a chemical reaction Enzymes lower the activation energy for chemical reactions For a reaction to begin the chemical bonds between the reactants must be broken which requires the molecules to absorb energy from their surroundings. This energy is caller Activation energy because it activates the reactants and triggers a chemical reaction. Enzymes lower the activation energy required to break the bonds of reactant molecules. It does so by bindng to reactant molecules and putting them under physical or chemical stress, making it easier to break their bonds and start a reaction.
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Enzymes and activation energy
energy barrier Activation energy barrier reduced by enzyme Enzyme Reactant Reactant Energy level Energy level Products Products (a) Without enzyme (b) With enzyme Figure 5.7 Enzymes and activation energy
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Induced Fit Every enzyme is very selective, catalyzing a specific reaction. Each enzyme recognizes a substrate, a specific reactant molecule. The active site fits to the substrate, and the enzyme changes shape slightly. This interaction is called induced fit because the entry of the substrate induces the enzyme to change shape slightly. Enzymes can function over and over again, a key characteristic of enzymes. Many enzymes are named for their substrates, but with an –ase ending The ability of the enzyme to recognize and bind to its specific substrate depends on the enzyme’s shape. The enzyme’s active site has a shape and chemistry that fit the substrate molecule.
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How an enzyme works How an enzyme works Substrate (sucrose)
Sucrase can accept a molecule of its substrate. Active site Substrate binds to the enzyme. Enzyme (sucrase) How an enzyme works Fructose H2O Glucose The products are released. The enzyme catalyzes the chemical reaction. Figure 5.9 How an enzyme works (Step 4)
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Enzyme Inhibitors Enzyme inhibitors can prevent metabolic reactions by binding to the active site. Inhibitor near the active site, resulting in changes to the enzyme’s shape so that the active site no longer accepts the substrate. Other enzyme inhibitors Bind at a remote site Change the enzyme’s shape Prevent the enzyme from binding to its substrate
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Enzyme inhibitors Substrate (a) Enzyme and substrate Active site
binding normally (b) Enzyme inhibition by a substrate imposter (c) Enzyme inhibition by a molecule that causes the active site to change shape Figure 5.10 Enzyme inhibitors
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Feedback regulation Some products of a reaction may inhibit the enzyme required for its production. This is called feedback regulation. It prevents the cell from wasting resources. Many antibiotics work by inhibiting enzymes of disease- causing bacteria. Penicillin blocks the active site of an enzyme that bacteria use in making cell walls. Ibuprofen inhibits an enzyme involved in sending pain signals. Many cancer drugs inhibit enzymes that promote cell division. In some cases, the binding is reversible, enabling certain inhibitors to regulate metabolism. For example, if metabolism is producing more of a certain product than a cell needs, that product may eversible inhibit an enzyme required for its production. This is called feedback regulation which prevents the cell from wasting resources. Antibiotics – penicillin Cancer drugs- cell division Nerve gas – nerve impulse pesticides
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MEMBRANE FUNCTION Working cells must control the flow of materials to and from the environment Cell membrane separates living cell from aqueous environment thin barrier = 8nm thick controls traffic in & out of the cell allows some substances to cross more easily than others hydrophobic (nonpolar) vs. hydrophilic (polar) Membrane proteins perform many functions Transport proteins are located in membranes, they regulate the passage of materials into and out of the cell So far we learned about how cells control the flow of energy and the pace of chemical ractions. They also must control the flow of materials to and from the environment
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Practice Which of the following describes the fluid-mosaic model of the plasma membrane structure? phospholipid monolayer with embedded proteins phospholipid bilayer with embedded proteins C) phospholipid trilayer with embedded proteins D) triglyceride bilayer with embedded proteins E) triglyceride monolayer with embedded proteins
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Practice Which of the following is NOT a characteristic of an animal plasma membrane? A) separates the internal environment of the cell from the external environment B) helps the cell maintain homeostasis C) responsible for the synthesis of ATP D) helps to maintain the cell's shape E) regulates passage of molecules into and out of the cell
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Permeability to polar molecules?
Phospholipid bilayer - Serves as a cellular barrier / border Transmembrane proteins embedded in phospholipid bilayer - specific channels allow specific material across cell membrane Membrane becomes semi-permeable via protein channels Fluid Mosaic model: Fluid: Phospholipids have fluid consistency like that of oil Mosaic: Proteins are scattered throughout Function: Maintains the cell’s shape, Regulates what goes into and out of cell inside cell H2O aa sugar Polar hydrophilic heads Nonpolar Hydrophobic tails Polar hydrophilic heads outside cell salt NH3
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Intercellular joining Cell-cell recognition
Cell signaling Enzymatic activity Cytoplasm Fibers of extracellular matrix Cytoskeleton Cytoplasm Intercellular joining Attachment to the cytoskeleton and extracellular matrix Transport Cell-cell recognition Figure 5.11 Figure 5.11 Primary functions of membrane proteins
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Passive Transport: Diffusion across Membranes
Molecules contain heat energy that causes them to vibrate and wander randomly. Diffusion is the tendency for molecules of any substance to spread out into the available space (example of passive transport) Passive transport is the diffusion of a substance across a membrane without the input of energy (O2 and CO2). Cell membranes are selectively permeable, allowing only certain substances to pass. Substances diffuse down their concentration gradient, a region in which the substance’s density changes.
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Passive transport: diffusion across a membrane
Molecules of dye Membrane (a) Passive transport of one type of molecule (b) Passive transport of two types of molecules Net diffusion Equilibrium Figure 5.12 Passive transport: diffusion across a membrane A substance will diffuse from where it is more concentrated to where it is less concentrated which mean substances diffuse down their concentration gradient. Passive transport of two types of molecules” each will diffuse down its own concentratrion gradient.
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Animation: How Diffusion works
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Passive transport: diffusion across a membrane
Some substances do not cross membranes spontaneously. These substances can be transported via facilitated diffusion. Specific transport proteins act as selective corridors. No energy input is needed.
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The Special Case of Water Movement of water across the cell membrane
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Osmosis and Water Balance
The diffusion of water across a selectively permeable membrane is osmosis (special kind of passive transport). The membrane allows water to pass but not the solute. the solution with the higher concentration is hypertonic and the one with lower solute is hypotonic. Hypotonic solution Hypertonic solution Sugar molecule Selectively permeable membrane Osmosis Isotonic solutions People can take the advantage of osmosis to preserve foods.
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Osmosis and Water Balance
Direction of osmosis is determined by comparing total solute concentrations Compared to another solution, A hypertonic solution has a higher concentration of solute than the cell A hypotonic solution has a lower concentration of solute than the cell An isotonic solution has an equal concentration of solute than the cell
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Animation: How Osmosis works
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Water Balance in Animal and Plant Cells
For living things to survive the different osmotic environments they need a way to balance the uptake and loss of water; the control of water balance within the cell is called osmoregulation. Most animal cells require an isotonic environment Plant have rigid cell walls. They require a hypotonic environment, which keeps these walled cells turgid. The survival of a cell depends on its ability to balance water uptake and loss. Most animal cells require an isotonic environment. For them to survive a hypotonic or hypertonic environment, they must have a way to balance an excessive uptake or excessive loss of water.
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The behavior of animal and plant cells in different osmotic environments
Animal cell Plant cell Normal Flaccid (wilts) Lysing Turgid Shriveled Plasma membrane H2O (a) Isotonic solution (b) Hypotonic solution (c) Hypertonic solution Figure 5.14 The behavior of animal and plant cells in different osmotic environments
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Water Balance in Plant Cells
As a plant cell loses water, it shrivels and its plasma membrane may pull away from the cell wall in the process of plasmolysis, which usually kills the cell. Figure 5.15 Plant turgor
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Practice Seawater is dangerous to drink because __________. ( Membrane Function) seawater is isotonic to your body fluids and you will absorb too much water, causing your cells to burst one cup of seawater contains enough sodium to poison you the salt causes hypertension and you will promptly die of a stroke seawater is hypertonic to your body tissues and drinking it will cause you to lose water by osmosis it contains toxic levels of iodine
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Practice If a red blood cell is placed in an isotonic solution,
water moves into and out of the cell at an equal rate. the cell will swell and then return to normal. the cell will shrivel the cell will swell and burst the cell will shrivel and then return to normal.
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Practice Crystals of dye, when placed in a beaker of water, eventually spread evenly throughout the water. This is an example of ______. Lipid-soluble molecules and gases enter the cell by ______. A) diffusion through the channel proteins B) osmosis through the channel proteins C) diffusion through the lipid bilayer D) osmosis through the lipid bilayer E) active transport through the lipid bilayer The diffusion of water across a differentially permeable membrane is called ______.
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Practice If two solutions have unequal concentrations of a solute, the solution with the lower concentration is called 1. hypotonic. 2. osmosis. 3. hypnotic. 4. isotonic. 5. hypertonic.
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Practice Which type of solution will cause cells to swell, or even to burst? Which type of solution has a lower percentage of solute than the cell? Which of the following processes uses a carrier protein and ATP? A) simple diffusion B) osmosis C) facilitated diffusion D) active transport E) endocytosis Which of the following comparisons is NOT correct? A) endocytosis--entering by sac B) exocytosis--leaving by sac C) active transport--against the gradient D) facilitated diffusion--with the gradient E) hypotonic solution--cells shrivel
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Practice An animal cell excretes a protein outside its membrane by the formation of a vesicle. Which process is involved in this transport? 1. endocytosis 2. osmosis 3. passive transport 4. exocytosis 5. phagocytosis
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Practice The diffusion of water across a selectively permeable membrane is called _____. ( Membrane Function) a. active transport b. osmosis c. exocytosis d. passive transport e. facilitated diffusion A plant cell placed in a hypotonic solution will not lyse because _____. ( Membrane Function) a. the cell wall prevents the plant cell from bursting b. it becomes turgid c. it shrivels d. plant plasma membranes are impermeable to water e. it is flaccid
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Practice Some liver cells ingest bacteria, a function probably accomplished by _____. ( Membrane Function) a. pinocytosis b. phagocytosis c. receptor-mediated d. endocytosis e. exocytosis f. passive transport The secretion of neurotransmitters out of the nerve cell, from small vesicles at the end of the axon, can be considered an example of _____. ( Membrane Function)
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Which beaker(s) contain(s) a solution that is hypertonic to the bag?
a. Which beaker(s) contain(s) a solution that is hypertonic to the bag? b. Which beaker(s) contain(s) a solution that is hypertonic to the bag? c. isotonic?
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Active Transport: The Pumping of Molecules Across Membranes
Active transport requires energy to move molecules across a membrane. Lower solute concentration Higher solute concentration ATP Solute Blast Animation: Active Transport: Sodium-Potassium Pump Animation: Active Transport © 2010 Pearson Education, Inc. AT enables the cells to maintain internal concentration of solutes that differ from environmental concentrations – the nerve cell has to maintain higher K conc and lower Na conc which is vital for the propagation of nerve signals. The PM helps maintain these differences by pumping Na out of the cell and K into the cell.
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Blast Animation: Active Transport: Sodium-Potassium Pump
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(requires no energy, down the concentration gradient,
MEMBRANE TRANSPORT Passive Transport (requires no energy, down the concentration gradient, movement of molecules from high to tow) Active Transport (requires energy, up against the gradient) Diffusion Facilitated diffusion Osmosis Higher solute concentration Higher water concentration (lower solute concentration) Higher solute concentration Solute Solute Solute Water Solute ATP Lower solute concentration Lower water concentration (higher solute concentration) Lower solute concentration Figure UN3 Summary: membrane transport
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Getting through cell membrane
Passive Transport Simple diffusion diffusion of nonpolar, hydrophobic molecules (lipids) HIGH LOW concentration gradient Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel Active transport diffusion against concentration gradient LOW HIGH uses a protein pump requires ATP ATP
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Practice Which one of the following is involved in facilitated diffusion? ( Membrane Function) Osmosis a concentration gradient an outside energy source a pump a nucleic acid
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Practice Which of the following is a difference between active transport and facilitated diffusion? ( Membrane Function) Facilitated diffusion requires energy from ATP, and active transport does not. Active transport requires the expenditure of cellular energy, and facilitated diffusion does not. Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. Facilitated diffusion involves transport proteins, and active transport does not. Active transport involves transport proteins, and facilitated diffusion does not.
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How about large molecules?
Moving large molecules into & out of cell through vesicles & vacuoles endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” exocytosis exocytosis
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Exocytosis and Endocytosis: Traffic of Large Molecules
Exocytosis is the secretion of large molecules within vesicles. It happens when secretory proteins exit the cell from transport vesicles that fuse with the plasma membrane, spilling the contents outside the cell. Outside of cell Cytoplasm Plasma membrane © 2010 Pearson Education, Inc. The movement of larger molecules into and out of the cell depends on the ability of the membrane to form sacs, thereby packaging the larger moleucules into sacs.
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Exocytosis and Endocytosis: Traffic of Large Molecules
Endocytosis is when cell takes material into a cell within vesicles that bud inward from the plasma membrane. So it "gulps" particle and packages it with a food vacuole.
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Summary: exocytosis and endocytosis
Figure UN4 Summary: exocytosis and endocytosis
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Exocytosis and Endocytosis: Traffic of Large Molecules
There are three types of endocytosis: Phagocytosis (“cellular eating”); a cell engulfs a particle and packages it within a food vacuole Pinocytosis (“cellular drinking”); a cell “gulps” droplets of fluid by forming tiny vesicles Receptor-mediated endocytosis; a cell takes in very specific molecules
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The Role of Membranes in Cell Signaling
The plasma membrane helps convey signals between cells and between cells and their environment Receptors on a cell surface trigger signal transduction pathways that relay the signal and convert it to chemical forms that can function within the cell
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An example of cell signaling
Outside of cell Cytoplasm Reception Transduction Response Receptor protein Epinephrine (adrenaline) from adrenal glands Plasma membrane Proteins of signal transduction pathway Hydrolysis of glycogen releases glucose for energy Figure 5.19 An example of cell signaling (detail) Communication begins when a receptor protein receives a stimulus from the outside environment or from a signaling molecule, hormone. This stimulus triggers a chain reaction in one or more molecules that function in transduction that relay the signal and convert it to chemical forms that can function within the cell. This signal leads to various response.
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Practice Which of the following is NOT an active method where molecules pass across the plasma membrane? simple diffusion active transport Endocytosis exocytosis The plasma membrane, because of the channel proteins, is said to be freely permeable. A) True B) False Macromolecules can freely cross a plasma membrane.
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Practice A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via _____. ( Membrane Function) Osmosis active transport Endocytosis Exocytosis passive transport
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Practice The secretion of neurotransmitters out of the nerve cell, from small vesicles at the end of the axon, can be considered an example of _____. ( Membrane Function) Pinocytosis Exocytosis Endocytosis Osmoregulation phagocytosis
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Practice Identify the energy needs of simple diffusion, osmosis, facilitated diffusion, active transport/solute pumping, endocytosis, and exocytosis. What type of transport uses protein carriers driven by the expenditure of chemical energy to move solute across a membrane against its concentration gradient? Osmosis active transport Exocytosis Diffusion facilitated transport
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Evolution Connection: The Origin of Membranes
Phospholipids are key ingredients of membranes, were probably among the first organic compounds that formed from chemical reactions on early Earth, and self-assemble into simple membranes. © 2013 Pearson Education, Inc. 67
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