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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell.

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Presentation on theme: "Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell."— Presentation transcript:

1 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 8 An Introduction to Metabolism

2 Concept 8.1: An organisms metabolism transforms matter and energy, subject to the laws of thermodynamics Metabolism is the totality of an organisms chemical reactions Metabolism is an emergent property of life that arises from interactions between molecules within the cell Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3 Enzyme 1Enzyme 2Enzyme 3 DCB A Reaction 1Reaction 3Reaction 2 Starting molecule Product Organization of the Chemistry of Life into Metabolic Pathways A metabolic pathway begins with a specific molecule and ends with a product Each step is catalyzed by a specific enzyme Catabolic pathways release energy by breaking down complex molecules into simpler compounds Cellular respiration, the breakdown of glucose in the presence of oxygen, is an example of a pathway of catabolism Anabolic pathways consume energy to build complex molecules from simpler ones The synthesis of protein from amino acids and photosynthesis are examples of anabolism Bioenergetics is the study of how organisms manage their energy resources

4 Forms of Energy Kinetic Energy – energy of motion; heat (thermal energy) is kinetic energy associated with the random movement of atoms or molecules Potential Energy – stored energy; the energy that matter possesses because of its location or structure Chemical Energy – refers to the potential energy available for release in chemical reactions

5 Fig. 8-2 Climbing up converts the kinetic energy of muscle movement to potential energy. A diver has less potential energy in the water than on the platform. Diving converts potential energy to kinetic energy. A diver has more potential energy on the platform than in the water.

6 (a) First law of thermodynamics(b) Second law of thermodynamics Chemical energy Heat CO 2 H2OH2O + Laws of Energy Transformation Thermodynamics – Study of the energy transformations First Law of Thermodynamics – The energy of the universe is constant. Energy/Matter can be transferred and transformed, but it cannot be created of destroyed Second Law of Thermodynamics – Every energy transfer of transformation increases the entropy (disorder/randomness) of the universe. Ordered forms of energy are at least partly converted to heat. CO 2 H2OH2O

7 Biological Order and Disorder Cells create ordered structures from less ordered materials Organisms also replace ordered forms of matter and energy with less ordered forms Energy flows into most ecosystems in the form of light and exits in the form of heat (Deep sea vents provide chemical energy in some marine ecosystems) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 50 µm

8 Fig. 8-5 (a) Gravitational motion – Objects move spontaneously from a higher altitude to a lower one (b) Diffusion – Molecules in a drop of dye diffuse until the are randomly dispersed (c) Chemical reaction – In a cell, a sugar molecule is broken down into simpler molecules. More free energy (higher G) Less stable Greater work capacity In a spontaneous change The free energy of the system decreases (G < 0) The system becomes more stable The released free energy can be harnessed to do work Less free energy (lower G) More stable Less work capacity

9 Fig. 8-6a Energy (a) Exergonic reaction: proceedes with a net release of free energy and is spontaneous Progress of the reaction Free energy Products Amount of energy released (G < 0) Reactants

10 Fig. 8-6b Energy (b) Endergonic reaction: absorbs free energy from its surrounding and is not spontaneous Progress of the reaction Free energy Products Amount of energy required (G > 0) Reactants

11 Fig. 8-7a (a) An isolated hydroelectric system. Water flowing downhill turns a turbines that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium G < 0G = 0

12 Fig. 8-7b (b) An open hydroelectric system – Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equilibrium. G < 0

13 Fig. 8-7c (c) A multistep open hydroelectric system – Cellular respiration is analogous to this system: Glucose is broken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium. G < 0

14 Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions A cell does three main kinds of work: – Chemical – The pushing of endergonic reactions, such as the building of polymers from monomers. – Transport – Active transport – Mechanical – Ex. – sister chromatides moving to opposite poles during cell division To do work, cells manage energy resources by energy coupling, the use of an exergonic process to drive an endergonic one (energy released from a downhill reaction can be used to drive an uphill reaction Most energy coupling in cells is mediated by ATP ATP (adenosine triphosphate) is the cells energy shuttle ATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction Overall, the coupled reactions are exergonic Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

15 Fig. 8-8 Phosphate groups Ribose Adenine

16 Fig. 8-9 Inorganic phosphate Energy Adenosine triphosphate (ATP) Adenosine diphosphate (ADP) P P P PP P + + H2OH2O i

17 Fig (b) Coupled with ATP hydrolysis, an exergonic reaction Ammonia displaces the phosphate group, forming glutamine. (a) Endergonic reaction (c) Overall free-energy change P P Glu NH 3 NH 2 Glu i ADP + P ATP + + Glu ATP phosphorylates glutamic acid, making the amino acid less stable. Glu NH 3 NH 2 Glu + Glutamic acid Glutamine Ammonia G = +3.4 kcal/mol + 2 1

18 ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant The recipient molecule is now phosphorylated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

19 Fig (b) Mechanical work: ATP binds noncovalently to motor proteins, then is hydrolyzed Membrane protein P i ADP + P Solute Solute transported P i VesicleCytoskeletal track Motor protein Protein moved (a) Transport work: ATP phosphorylates transport proteins ATP ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant or protein The recipient molecule is now phosphorylated

20 Fig P i ADP+ Energy from catabolism (exergonic, energy-releasing processes) Energy for cellular work (endergonic, energy-consuming processes) ATP + H2OH2O The Regeneration of ATP ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP) The energy to phosphorylate ADP comes from catabolic reactions in the cell The chemical potential energy temporarily stored in ATP drives most cellular work

21 Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction An enzyme is a catalytic protein Hydrolysis of sucrose by the enzyme sucrase is an example of an enzyme-catalyzed reaction Enzymes catalyze reactions by lowering the E A barrier Enzymes do not affect the change in free energy (G); instead, they hasten reactions that would occur eventually Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

22 Fig Sucrose (C 12 H 22 O 11 ) Glucose (C 6 H 12 O 6 ) Fructose (C 6 H 12 O 6 ) Sucrase

23 Fig Progress of the reaction Products Reactants G < O Transition state Free energy EAEA DC BA D D C C B B A A

24 Fig Progress of the reaction Products Reactants G is unaffected by enzyme Course of reaction without enzyme Free energy E A without enzyme E A with enzyme is lower Course of reaction with enzyme

25 Fig Substrates Enzyme Products are released. Products Substrates are converted to products. Active site can lower E A and speed up a reaction. Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrates enter active site; enzyme changes shape such that its active site enfolds the substrates (induced fit). Active site is available for two new substrate molecules. Enzyme-substrate complex The active site can lower an EA barrier by – Orienting substrates correctly – Straining substrate bonds – Providing a favorable microenvironment – Covalently bonding to the substrate

26 Substrate Active site Enzyme Enzyme-substrate complex When the substrate enters the active site, it induces a change in the shape of the protein, allowing more weak bonds to form, causing the active site to Enfold the substrate and hold it in place. The active site of the enzyme forms a groove on its surface.

27 Fig Rate of reaction Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Optimal temperature for typical human enzyme (a) Optimal temperature for two enzymes (b) Optimal pH for two enzymes Rate of reaction Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) Temperature (ºC) pH Each enzyme has an optimal temperature in which it can function Each enzyme has an optimal pH in which it can function

28 Cofactors Cofactors are nonprotein enzyme helpers Cofactors may be inorganic (such as a metal in ionic form) or organic An organic cofactor is called a coenzyme Coenzymes include vitamins Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

29 (a) Normal binding(c) Noncompetitive inhibition(b) Competitive inhibition Noncompetitive inhibitor Active site Competitive inhibitor Substrate Enzyme Enzyme Inhibitors Competitive inhibitors bind to the active site of an enzyme, competing with the substrate Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective Examples of inhibitors include toxins, poisons, pesticides, and antibiotics

30 Concept 8.5: Regulation of enzyme activity helps control metabolism Chemical chaos would result if a cells metabolic pathways were not tightly regulated A cell does this by switching on or off the genes that encode specific enzymes or by regulating the activity of enzymes Allosteric regulation may either inhibit or stimulate an enzymes activity Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and affects the proteins function at another site Most allosterically regulated enzymes are made from polypeptide subunits Each enzyme has active and inactive forms The binding of an activator stabilizes the active form of the enzyme The binding of an inhibitor stabilizes the inactive form of the enzyme Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

31 Fig. 8-20a (a) Allosteric activators and inhibitors Inhibitor Non- functional active site Stabilized inactive form Inactive form Oscillation Activator Active formStabilized active form Regulatory site (one of four) Allosteric enzyme with four subunits Active site (one of four)

32 Fig. 8-20b (b) Cooperativity: another type of allosteric activation Stabilized active form Substrate Inactive form Cooperativity is a form of allosteric regulation that can amplify enzyme activity In cooperativity, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits

33 Feedback Inhibition In feedback inhibition, the end product of a metabolic pathway shuts down the pathway Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

34 Fig Intermediate C Feedback inhibition Isoleucine used up by cell Enzyme 1 (threonine deaminase) End product (isoleucine) Enzyme 5 Intermediate D Intermediate B Intermediate A Enzyme 4 Enzyme 2 Enzyme 3 Initial substrate (threonine) Threonine in active site Active site available Active site of enzyme 1 no longer binds threonine; pathway is switched off. Isoleucine binds to allosteric site

35 Fig µm Mitochondria Structures within the cell help bring order to metabolic pathways Some enzymes act as structural components of membranes In eukaryotic cells, some enzymes reside in specific organelles; for example, enzymes for cellular respiration are located in mitochondria Specific Localization of Enzymes Within the Cell

36 You should now be able to: 1.Distinguish between the following pairs of terms: catabolic and anabolic pathways; kinetic and potential energy; open and closed systems; exergonic and endergonic reactions 2.In your own words, explain the second law of thermodynamics and explain why it is not violated by living organisms 3.Explain in general terms how cells obtain the energy to do cellular work 4.Explain how ATP performs cellular work 5.Explain why an investment of activation energy is necessary to initiate a spontaneous reaction 6.Describe the mechanisms by which enzymes lower activation energy 7.Describe how allosteric regulators may inhibit or stimulate the activity of an enzyme Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

37 Fig. 8-UN2 Progress of the reaction Products Reactants G is unaffected by enzyme Course of reaction without enzyme Free energy E A without enzyme E A with enzyme is lower Course of reaction with enzyme

38 Fig. 8-UN3

39 Fig. 8-UN4

40 Fig. 8-UN5


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