Chapter 8 An Introduction to Metabolism Power Point

Chapter 8 An Introduction to Metabolism Power. Point Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Overview: The Energy of Life • The living cell – Is a miniature factory where thousands of reactions occur – Converts energy in many ways Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Some organisms – Convert energy to light, as in bioluminescence Figure 8.

• Concept 8. 1: An organism’s metabolism transforms matter and energy, subject to

Metabolism – Is the totality of an organism’s chemical reactions – Arises from interactions between molecules • Catabolic pathways – Break down complex molecules into simpler compounds – Release energy • Anabolic pathways – Build complicated molecules from simpler ones – Consume energy Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Organization of the Chemistry of Life into Metabolic Pathways • A metabolic pathway has many steps – That begin with a specific molecule and end with a product – That are each catalyzed by a specific enzyme Enzyme 1 A Enzyme 2 D C B Reaction 1 Enzyme 3 Reaction 2 Starting molecule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reaction 3 Product

Forms of Energy • Energy – Is the capacity to cause change – Exists in various forms, of which some can perform work Radiant/light Thermal/Heat Electrical Mechanical (kinetic) Chemical Nuclear Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Kinetic energy – Is the energy associated with motion • Potential energy – Is stored in the location of matter – Includes chemical energy stored in molecular structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Energy can be converted – From one form to another On the platform, a diver has more potential energy. Figure 8. 2 Climbing up converts kinetic energy of muscle movement to potential energy. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diving converts potential energy to kinetic energy. In the water, a diver has less potential energy.

The Laws of Energy Transformation • Thermodynamics – Is the study of energy transformations

The First Law of Thermodynamics • According to the first law of thermodynamics, – Energy can be changed from one form to another, but it cannot be created or destroyed. Chemical energy Figure 8. 3 (a) First law of thermodynamics: Energy can be transferred or transformed but Neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b). Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Implication: The total amount of energy and matter in the Universe remains constant, merely changing from one form to another.

The Second Law of Thermodynamics • In all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state. " • This is also commonly referred to as entropy. • Examples: – A watchspring-driven watch will run until the potential energy in the spring is converted, and not again until energy is reapplied to the spring to rewind it. – A car that has run out of gas will not run again until you walk 10 miles to a gas station and refuel the car. – Once the potential energy locked in carbohydrates is converted into kinetic energy (energy in use or motion), the organism will get no more until energy is input again. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Biological Order and Disorder • Living systems increase the entropy (S) of the universe – Energy must be input to maintain order Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Second Law of Thermodynamics • Energy IN = Energy OUT + dissipates • In the process of energy transfer, some energy will dissipate as heat. Term: dissipates = “lost” energy (ex: body heat). No longer ‘available’ to do work Figure 8. 3 Heat co 2 + H 2 O (b) Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Entropy • Entropy is a measure of disorder: cells are NOT disordered and so have low entropy. • The flow of energy maintains order and life. • Entropy wins when organisms cease to take in energy and die. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Free-Energy Change, G • A living system’s free energy – Is energy that can do work under cellular conditions • The free-energy change of a reaction tells us whether the reaction occurs spontaneously Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The change in free energy, ∆G during a biological process – Is related directly to the enthalpy change (∆H) and the change in entropy ∆G = ∆H – T∆S In chemical reactions, the total enthalpy (H) is the amount of energy stored in all of the bonds; that is, the amount of energy it would require to break all of the bonds. Generally this is expressed as heatreleasing (exothermic) or heat-absorbing (endothermic) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Free Energy, Stability, and Equilibrium • Organisms live at the expense of free energy • During a spontaneous change – Free energy decreases and the stability of a system increases If the amount of energy released from breaking bonds is more than the energy required to make bonds, then overall, the reaction will release energy. = negative free energy change (exergonic) - ∆G Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Exergonic Reactions in Metabolism • An exergonic reaction (- ∆G ) – Proceeds with a net release of free energy and is spontaneous Reactants Free energy Amount of energy released (∆G <0) Energy Products Progress of the reaction Figure 8. 6 (a) Exergonic reaction: energy released Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Endergonic Reactions in Metabolism • An endergonic reaction (+ ∆G ) – Is one that absorbs free energy from its surroundings and is non spontaneous (requires energy input) Free energy Products Energy Reactants Progress of the reaction Figure 8. 6 (b) Endergonic reaction: energy required Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amount of energy released (∆G>0)

Equilibrium and Metabolism • Reactions in a closed system – Eventually reach equilibrium ∆G < 0 Figure 8. 7 A ∆G = 0 (a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Cells in our body exist in an OPEN system – Experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium (b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium. Figure 8. 7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ∆G < 0 A cell does three main kinds of work: • Mechanical • Transport • Chemical

Coupling reactions • Concept 8. 3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions In other words, in a series of linked reactions, the steps that have -∆G (exergonic) can “pull” along those steps that require energy (endergonic, +∆G ) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• An analogy for cellular respiration, a biochemical pathway of linked chemical reactions ∆G < 0 Figure 8. 7 (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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Energy coupling Is a key feature in the way cells manage their energy resources to do this work In other words, in a series of linked reactions, the steps that have -∆G (exergonic) can “pull” along those steps that require energy (endergonic, +∆G ) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Structure and Hydrolysis of ATP • ATP (adenosine triphosphate) – Is the cell’s energy shuttle – Provides energy for cellular functions Adenine N O O - O - O O C C N HC O O O NH 2 - Phosphate groups Figure 8. 8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings N CH 2 O H N H H H OH CH C OH Ribose

• Energy is released from ATP – When the terminal phosphate bond is broken P P P Adenosine triphosphate (ATP) H 2 O P i + Figure 8. 9 Inorganic phosphate P P Adenosine diphosphate (ADP) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy

Energy coupling – Can be coupled to other reactions Endergonic reaction: ∆G is positive, reaction is not spontaneous NH 2 Glu + Glutamic acid NH 3 Glu Ammonia Glutamine ∆G = +3. 4 kcal/mol Exergonic reaction: ∆ G is negative, reaction is spontaneous ATP + H 2 O ADP + Coupled reactions: Overall ∆G is negative; Figure 8. 10 together, reactions are spontaneous Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings P ∆G = - 7. 3 kcal/mol ∆G = – 3. 9 kcal/mol

How ATP Performs Work • ATP drives endergonic reactions – By phosphorylation, transferring a

The Regeneration of ATP • Catabolic pathways – Drive the regeneration of ATP from ADP and phosphate ATP hydrolysis to ADP + P i yields energy ATP synthesis from ADP + P i requires energy ATP Energy from catabolism (exergonic, energy yielding processes) Figure 8. 12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy for cellular work (endergonic, energyconsuming processes) ADP + P i

The Role of Enzymes in Energetics • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Activation Barrier • Every chemical reaction between molecules – Involves both bond breaking and forming bonds. • The hydrolysis of a disaccharide is an example: CH 2 OH O O H H OH H HO O + CH 2 OH H Sucrase H 2 O OH H OH CH 2 OH O H H H OH HO H OH CH 2 OH O HO H CH 2 OH OH H Sucrose Glucose Fructose C 12 H 22 O 11 C 6 H 12 O 6 Figure 8. 13 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Chemical Reactions • The activation energy, EA – Is the initial amount of energy needed to start a chemical reaction – Is often supplied in the form of heat from the surroundings in a system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The effect of enzymes on reaction rate • An enzyme catalyzes reactions – By lowering the EA barrier Free energy Course of reaction without enzyme EA with enzyme is lower Reactants Course of reaction with enzyme ∆G is unaffected by enzyme Products Figure 8. 15 Progress of the reaction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Substrate Specificity of Enzymes • The substrate (A) – Is the reactant an enzyme acts on • The enzyme – Binds to its substrate, forming an enzymesubstrate complex (C) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The active site – Is the region on the enzyme where the substrate binds • Their shape (conformation) makes each enzyme substratespecific • “Lock-and-key” fit enables reaction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• The active site can lower an EA barrier by – Orienting substrates correctly – Straining substrate bonds – Providing a favorable microenvironment – Covalently bonding to the substrate Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Effects of Local Conditions on Enzyme Activity • The activity of an enzyme – Is affected by general environmental factors • temperature • p. H • salinity • enzyme concentration • substrate concentration • presence of any inhibitors or activators. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Denaturation is a process in which proteins or nucleic acids lose their tertiary structure and secondary structure by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent (e. g. , alcohol or chloroform), or heat. • If proteins in a living cell are denatured, this results in disruption of cell activity and possibly cell death. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Effects of Temperature and p. H • Each enzyme – Has an optimal temperature in which it can function Optimal temperature for typical human enzyme Optimal temperature for enzyme of thermophilic Rate of reaction (heat-tolerant) bacteria 0 20 40 Temperature (Cº) (a) Optimal temperature for two enzymes Figure 8. 18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 80 100

– Has an optimal p. H in which it can function Optimal p. H for pepsin (stomach enzyme) Rate of reaction Optimal p. H for trypsin (intestinal enzyme) 3 4 0 2 1 (b) Optimal p. H for two enzymes Figure 8. 18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5 6 7 8 9

Cofactors & Coenzymes • Cofactors – Are nonprotein enzyme helpers – Most often minerals (metal ions) – Zn 2+, Mg 2+ • Coenzymes – Are organic cofactors – Usually vitamins – B 2, B 6, B 12, etc Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Enzymes Regulate reactions • Concept 8. 5: Regulation of enzyme activity helps control metabolism • A cell’s metabolic pathways – Must be tightly regulated Enzyme 1 A Enzyme 2 D C B Reaction 1 Enzyme 3 Reaction 2 Starting molecule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reaction 3 Product

Allosteric Activation and Inhibition • Many enzymes are allosterically regulated • Allosteric regulation – Is the term used to describe any case in which a protein’s function at one site is affected by binding of a regulatory molecule at another site – Enzymes can be “turned on” or “turned off” this way Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Enzyme Inhibitors • Competitive inhibitors – Bind to the active site of an enzyme, competing with the substrate A substrate can bind normally to the active site of an enzyme. Substrate Active site Enzyme (a) Normal binding A competitive inhibitor mimics the substrate, competing for the active site. Figure 8. 19 (b) Competitive inhibition Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Competitive inhibitor

Noncompetitive inhibitors • Noncompetitive inhibitors – Bind to another part of an enzyme, changing the function A noncompetitive inhibitor binds to the enzyme away from the active site, altering the conformation of the enzyme so that its active site no longer functions. Noncompetitive inhibitor Figure 8. 19 (c) Noncompetitive inhibition Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Feedback inhibition • In feedback inhibition Active site available – The end product of a metabolic pathway shuts down the pathway Isoleucine used up by cell Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Intermediate A Feedback inhibition Active site of Enzyme 2 enzyme 1 no longer binds Intermediate B threonine; pathway is Enzyme 3 switched off Intermediate C Isoleucine binds to allosteric site Enzyme 4 Intermediate D Enzyme 5 Figure 8. 21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings End product (isoleucine)

– Eukaryotic cells improve effectiveness by “compartmentalizing” their enzymatic processes – Contained inside organelles Mitochondria, sites of cellular respiraion Figure 8. 22 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1 µm