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  • {"38":"Figure 5.14_s3 The catalytic cycle of an enzyme (step 3)\n","27":"Figure 5.9 Three kinds of endocytosis\n","16":"Student Misconceptions and Concerns\nStudents easily confuse the term hypertonic and hypotonic. One challenge is to get them to understand that these are relative terms, such as heavier, darker, or fewer. No single object is heavier, no single cup of coffee is darker, and no single bag of M & M’s has fewer candies. Such terms only apply when comparing two or more items. A solution with a higher concentration than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution.\nTeaching Tips\n1. The word root hypo means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s).\n2. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic)\n3. The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations.\n","5":"Figure 5.2Q Structure of membrane sacs\n","33":"Figure 5.13Q Activation energy with and without an enzyme\n","22":"Figure 5.6 Transport protein providing a channel for the diffusion of a specific solute across a membrane\n","11":"Figure 5.3A Passive transport of one type of molecule\n","39":"Figure 5.14_s4 The catalytic cycle of an enzyme (step 4)\n","28":"Student Misconceptions and Concerns\n1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples.\n2. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well.\nTeaching Tips\n1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.)\n2. When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots tri = 3 and di = 2. It might help students to keep track of the number of phosphates more easily.\n3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population).\n","6":"Teaching Tips\nYou might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.)\n","34":"Student Misconceptions and Concerns\nFor students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output is much greater than the input. \nTeaching Tips\nThe information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids.\n","23":"Teaching Tips\n1. Active transport uses energy to move a solute against its concentration gradient. Challenge your students to think of the many possible analogies to this situation, for example, bailing out a leaky boat by moving water back to a place (outside the boat) where water is more concentrated. An alternative analogy might be the herding of animals, which requires work to keep the organisms concentrated and counteract their natural tendency to spread out.\n2. Students familiar with city subway toll stations might think of some gate mechanisms that work similarly to the proteins regulating active transport. A person steps up to a barrier and inserts payment (analogous to ATP input), and the gate changes shape, permitting passage to the other side. Even a simple turnstile system that requires payment is generally similar.\n","12":"Figure 5.3B Passive transport of two types of molecules\n","40":"Student Misconceptions and Concerns\nThe specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support.\nTeaching Tips\n1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids.\n2. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments.\n","29":"Figure 5.12A_s1 The structure and hydrolysis of ATP (step 1)\n","7":"Teaching Tips\nYou might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.)\n","35":"Student Misconceptions and Concerns\nThe specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support.\nTeaching Tips\n1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids.\n2. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments.\n","24":"Figure 5.UN01 Reviewing the Concepts, 5.8\n","13":"Student Misconceptions and Concerns\nFor students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives.\nTeaching Tips\nYour students may have noticed that the skin of their fingers wrinkles after taking a long shower or bath, or after washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Through osmosis, water moves into the epidermal skin cells. Our skin is hypertonic to these solutions, producing the swelling that appears as large wrinkles. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water because the soap removes the natural layer of oil from our skin. \n","2":"Figure 5.0_1 Chapter 5: Big Ideas\n","41":"Student Misconceptions and Concerns\nThe specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support.\nTeaching Tips\n1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids.\n2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.)\n3. Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class to suggest other products of reactions that inhibit the process that made them when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced.)\n","30":"Figure 5.12A_s2 The structure and hydrolysis of ATP (step 2)\n","19":"Figure 5.5 How animal and plant cells react to changes in tonicity\n","8":"Figure 5.1 Some functions of membrane proteins\n","36":"Figure 5.14_s1 The catalytic cycle of an enzyme (step 1)\n","25":"Teaching Tips\nStudents carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Consider challenging your students to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.)\n","14":"Figure 5.4 Osmosis, the diffusion of water across a membrane\n","42":"Student Misconceptions and Concerns\nThe specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support.\nTeaching Tips\n1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids.\n2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.)\n3. Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class to suggest other products of reactions that inhibit the process that made them when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced.)\n","31":"Student Misconceptions and Concerns\n1. Students with limited exposure to physics may have never understood the concepts of energy and the conservation of energy or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples.\n2. Energy coupling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well.\nTeaching Tips\n1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon the size and activity of a person, a human might burn 2,000 dietary calories (kilocalories) a day. This is enough energy to raise the temperature of 20 liters of liquid water from 0 to 100C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.)\n2. When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots tri = 3 and di = 2. It might help students to keep track of the number of phosphates more easily.\n3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. Both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population).\n","20":"Teaching Tips\nThe text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium.\n","9":"Student Misconceptions and Concerns\nFor students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives.\nTeaching Tips \n1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of perfume or cologne from a bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away.\n2. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. The fan from an active overhead projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration.\n","37":"Figure 5.14_s2 The catalytic cycle of an enzyme (step 2)\n","26":"Teaching Tips\nStudents carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Consider challenging your students to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.)\n","15":"Student Misconceptions and Concerns\nStudents easily confuse the term hypertonic and hypotonic. One challenge is to get them to understand that these are relative terms, such as heavier, darker, or fewer. No single object is heavier, no single cup of coffee is darker, and no single bag of M & M’s has fewer candies. Such terms only apply when comparing two or more items. A solution with a higher concentration than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution.\nTeaching Tips\n1. The word root hypo means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s).\n2. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic)\n3. The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations.\n","4":"Teaching Tips\nYou might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.)\n","43":"Figure 5.15A How inhibitors interfere with substrate binding\n","32":"Student Misconceptions and Concerns\nFor students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output is much greater than the input. \nTeaching Tips\nThe information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids.\n","21":"Teaching Tips\nThe text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium.\n","10":"Student Misconceptions and Concerns\nFor students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives.\nTeaching Tips \n1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of perfume or cologne from a bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away.\n2. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. The fan from an active overhead projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration.\n"}

Biology 2 Chapter 5 notes Biology 2 Chapter 5 notes Presentation Transcript

  • Chapter 5 The Working Cell PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko
  • Figure 5.0_1 Chapter 5: Big Ideas Cellular respiration Membrane Structure and Function How Enzymes Function Energy and the Cell
  • Introduction  Many of a cell’s reactions – take place in organelles and – use enzymes embedded in the membranes of these organelles.  This chapter addresses how working cells use membranes, energy, and enzymes. © 2012 Pearson Education, Inc.
  • 5.1 Membranes are fluid mosaics of lipids and proteins with many functions  Membranes are composed of – a bilayer of phospholipids with – embedded and attached proteins, – Biologists call this structure a fluid mosaic. © 2012 Pearson Education, Inc.
  • 5.1  Remember phospholipids have two hydrophobic tails and a hydrophilic head. Water  Why do they remain fluid? Water
  • 5.1  Membrane proteins perform many functions. 1. Some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the cytoskeleton and extracellular matrix. 2. Some proteins function as receptors for chemical messengers from other cells. 3. Some membrane proteins function as enzymes. © 2012 Pearson Education, Inc.
  • 5.1 4. Some membrane glycoproteins are involved in cell-cell recognition. 5. Membrane proteins may participate in the intercellular junctions that attach adjacent cells to each other. 6. Membranes may exhibit selective permeability, allowing some substances to cross more easily than others. © 2012 Pearson Education, Inc.
  • Figure 5.1 CYTOPLASM Enzymatic activity Fibers of extracellular matrix (ECM) Phospholipid Cholesterol Cell-cell recognition Receptor Signaling molecule Transport Attachment to the cytoskeleton and extracellular matrix (ECM) Signal transduction ATP Intercellular junctions Microfilaments of cytoskeleton Glycoprotein CYTOPLASM
  • 5.3 Passive transport is diffusion across a membrane with no energy investment  Diffusion is the tendency of particles to spread out evenly in an available space. – Particles move from an area of more concentrated particles to an area where they are less concentrated. – This means that particles diffuse down their concentration gradient. – Eventually, the particles reach equilibrium where the concentration of particles is the same throughout.  Diffusion across a cell membrane does not require energy, so it is called passive transport. © 2012 Pearson Education, Inc.
  • 5.3 Animation: Diffusion Animation: Membrane Selectivity © 2012 Pearson Education, Inc.
  • Figure 5.3A Molecules of dye Membrane Pores Net diffusion Net diffusion Equilibrium
  • Figure 5.3B Net diffusion Net diffusion Equilibrium Net diffusion Net diffusion Equilibrium
  • 5.4 Osmosis is the diffusion of water across a membrane  One of the most important substances that crosses membranes is water.  The diffusion of water across a selectively permeable membrane is called osmosis. Animation: Osmosis © 2012 Pearson Education, Inc.
  • Figure 5.4 Lower Higher concentration concentration of solute of solute Solute molecule Equal concentrations of solute H2O Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Osmosis
  • 5.5 Water balance between cells and their surroundings is crucial to organisms  Tonicity is a term that describes the ability of a solution to cause a cell to gain or lose water.  Tonicity mostly depends on the concentration of a solute on both sides of the membrane. © 2012 Pearson Education, Inc.
  • How will animal cells be affected when placed into solutions of various tonicities?  When an animal cell is placed into an isotonic solution – the concentration of solute is the same on both sides of a membrane – Water will move in and out of the cell at the same rate – the cell volume will not change © 2012 Pearson Education, Inc.
  • When an animal cell is placed into a hypotonic solution  the solute concentration is lower outside the cell,  water molecules move into the cell,  the cell will expand and may burst
  • When an animal cell is placed into a hypertonic solution  the solute concentration is higher outside the cell  water molecules move out of the cell  the cell will shrink
  • Figure 5.5 Hypotonic solution H2O Isotonic solution Hypertonic solution H2O H2O H2O Animal cell Normal Lysed Plasma membrane H2O H2O Shriveled H2O Plant cell Turgid (normal) Flaccid Shriveled (plasmolyzed)
  • 5.6 Transport proteins can facilitate diffusion across membranes  Polar or charged substances do not move easily through the cell membrane – instead, they must move across membranes with the help of specific transport proteins in a process called facilitated diffusion – does not require energy and – relies on the concentration gradient. © 2012 Pearson Education, Inc.
  • 5.6  Some proteins function by becoming a tunnel for passage of ions or other molecules.  Other proteins bind their passenger, change shape, and release their passenger on the other side. – In both of these situations, the protein is specific for the substrate. © 2012 Pearson Education, Inc.
  • Figure 5.6 Solute molecule Transport protein
  • 5.8 Cells expend energy in the active transport of a solute  In active transport, a cell – must expend energy to move a solute against its concentration gradient. Animation: Active Transport © 2012 Pearson Education, Inc.
  • Figure 5.UN01 Passive transport (requires no energy) Diffusion Facilitated diffusion HIgher solute concentration Active transport (requires energy) Osmosis HIgher free water concentration HIgher solute concentration Solute Water Lower solute concentration Lower free water concentration ATP Lower solute concentration
  • 5.9 Exocytosis and endocytosis transport large molecules across membranes  A cell uses two mechanisms to move large molecules across membranes. – Exocytosis is used to export bulky molecules, such as proteins or polysaccharides. – Endocytosis is used to import substances useful to the livelihood of the cell.  In both cases, material to be transported is packaged within a vesicle that fuses with the membrane. © 2012 Pearson Education, Inc.
  • 5.9 Exocytosis and endocytosis transport large molecules across membranes  There are three kinds of endocytosis. 1. Phagocytosis is the engulfment of a particle by wrapping cell membrane around it, forming a vacuole. 2. Pinocytosis is the same thing except that fluids are taken into small vesicles. 3. Receptor-mediated endocytosis uses receptors in a receptor-coated pit to interact with a specific protein, initiating the formation of a vesicle. Animation: Exocytosis and Endocytosis © 2012 Pearson Education, Inc.
  • Figure 5.9 Phagocytosis EXTRACELLULAR FLUID Pseudopodium CYTOPLASM Food being ingested “Food” or other particle Food vacuole Pinocytosis Plasma membrane Vesicle Receptor-mediated endocytosis Coat protein Receptor Plasma membrane Coated vesicle Coated pit Specific molecule Coated pit Material bound to receptor proteins
  • 5.12 ATP drives cellular work by coupling exergonic and endergonic reactions  ATP, adenosine triphosphate, powers nearly all forms of cellular work.  ATP consists of – the nitrogenous base adenine, – the five-carbon sugar ribose, and – three phosphate groups.  Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called phosphorylation. © 2012 Pearson Education, Inc.
  • Figure 5.12A_s1 ATP: Adenosine Triphosphate Phosphate group Adenine Ribose P P P
  • Figure 5.12A_s2 ATP: Adenosine Triphosphate Phosphate group P P Adenine P Ribose Hydrolysis P ADP: H2O P Adenosine Diphosphate P Energy
  • 5.12  ATP is a renewable source of energy for the cell.  In the ATP cycle, energy released in an exergonic reaction, such as the breakdown of glucose,is used in an endergonic reaction to generate ATP. © 2012 Pearson Education, Inc.
  • 5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers  Within the cell an energy barrier must be overcome before a chemical reaction can begin. – This energy is called the activation energy (EA).  We can think of EA – as the amount of energy needed for a reactant molecule to move “uphill” to a higher energy but an unstable state – so that the “downhill” part of the reaction can begin. © 2012 Pearson Education, Inc.
  • Figure 5.13Q Energy a b Reactants c Products Progress of the reaction
  • 5.13  Enzymes – function as biological catalysts by lowering the EA needed for a reaction to begin – increase the rate of a reaction without being consumed by the reaction – are usually proteins Animation: How Enzymes Work © 2012 Pearson Education, Inc.
  • 5.14 A specific enzyme catalyzes each cellular reaction  An enzyme – is very selective in the reaction it catalyzes and – has a shape that determines the enzyme’s specificity.  The specific reactant that an enzyme acts on is called the enzyme’s substrate.  A substrate fits into a region of the enzyme called the active site.  Enzymes are specific because their active site fits only specific substrate molecules. © 2012 Pearson Education, Inc.
  • Figure 5.14_s1 1 Enzyme available with empty active site Active site Enzyme (sucrase)
  • Figure 5.14_s2 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Enzyme (sucrase) Substrate binds to enzyme with induced fit
  • Figure 5.14_s3 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme (sucrase) H2O 3 Substrate is converted to products
  • Figure 5.14_s4 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Glucose Substrate binds to enzyme with induced fit Enzyme (sucrase) Fructose H2O 4 Products are released 3 Substrate is converted to products
  • 5.14  For every enzyme, there are optimal conditions under which it is most effective.  Temperature affects molecular motion. – An enzyme’s optimal temperature produces the highest rate of contact between the reactants and the enzyme’s active site. – Most human enzymes work best at 35–40ºC.  The optimal pH for most enzymes is near neutrality. © 2012 Pearson Education, Inc.
  • 5.15 Enzyme inhibitors can regulate enzyme activity in a cell  A chemical that interferes with an enzyme’s activity is called an inhibitor.  Competitive inhibitors – block substrates from entering the active site and – reduce an enzyme’s productivity. © 2012 Pearson Education, Inc.
  • 5.15 Enzyme inhibitors can regulate enzyme activity in a cell  Noncompetitive inhibitors – bind to the enzyme somewhere other than the active site – change the shape of the active site – prevent the substrate from binding © 2012 Pearson Education, Inc.
  • Figure 5.15A Substrate Active site Enzyme Allosteric site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Enzyme inhibition
  • You should now be able to 1. Describe the fluid mosaic structure of cell membranes. 2. Describe the diverse functions of membrane proteins. 3. Relate the structure of phospholipid molecules to the structure and properties of cell membranes. 4. Define diffusion and describe the process of passive transport. © 2012 Pearson Education, Inc.
  • You should now be able to 5. Explain how osmosis can be defined as the diffusion of water across a membrane. 6. Distinguish between hypertonic, hypotonic, and isotonic solutions. 7. Explain how transport proteins facilitate diffusion. 8. Distinguish between exocytosis, endocytosis, phagocytosis, pinocytosis, and receptor-mediated endocytosis. © 2012 Pearson Education, Inc.
  • You should now be able to 9. Explain how ATP functions as an energy shuttle. 10. Explain how enzymes speed up chemical reactions. 11. Explain how competitive and noncompetitive inhibitors alter an enzyme’s activity. © 2012 Pearson Education, Inc.