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Overview: The Energy of Life

y The living cell is a miniature factory where thousands of reactions occur and convertsenergy in many ways

An organisms metabolism transforms matter and energy, subject to the laws of

thermodynamics

y Metabolism- all of an organisms chemical reactionsOrganization of the Chemistry of Life into Metabolic Pathways

y Metabolic pathway- begins w/ a specific molecule which is then altered in a series ofdefined steps, resulting in a product.

y Catabolic pathways- break down pathway,release energyy Anabolic pathways- consume energy to build complicated molecules from simpler ones

Forms of Energy

y Energy- the capacity to cause changey Kinetic energy- energy associated w/ the relative motion of objectsy Heat or thermal energy is kinetic energy associated w/ the random movement of atoms

or molecules

y Potential energy- is energy that matter possesses b/c of its location or structurey Chemical energy- the potential energy available for release in a chemical reactiony Energy can be converted from one form to another:

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The Laws of Energy Transformation

y Thermodynamics- the study of energy transformations that occur in a collection ofmatter

y According to the first law of thermodynamics- energy can be transferred andtransformed, but it cannot be created or destroyed(principle of conservation of energy)

y According to the second law of thermodynamics- every energy transfer oftransformation increases the entropy of the universe

y Entropy- a measure of disorder, or randomnessy For a process to occur spontaneously, it must increase the entropy of the universe

Biological Order and Disorder

y Universe- the system plus its surroundingsThe free-energy change of a reaction tells us whether the reaction occurs spontaneously

Free- Energy Change, (G

y Free energy- measures the portion of a systems energy that can perform work whentemp and press. are uniform, as in a cell

y The change in free energy, Gduring a biological process, can be calculated for anyspecific chemical reaction w/ this formula:

G = H TS

y H symbolizes the change in the systems enthalpy(= total energy), S is the change inthe systems entropy, and T is the absolute temp on Kelvin(K)

Free Energy, Stability, and Equilibrium

y Organisms live at the expense offree energyy During a spontaneous change free energy decreases and the stability of a system

increases

y Equilibrium- term for a state of maximum stability

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Free Energy and Metabolism

Exergonic andEndergonic ReactionsinMetabolism

y Exergonic reaction- proceeds with a net release of free energy and is spontaneous

y Endergonic reaction- absorbs free energy from its surroundings and is nonspontaneous

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Equilibrium and Metabolism

y Reactions in a closed system eventually reach equilibrium and can then do work

y Cells in our body- experience a constant flow of materials in and out, preventingmetabolic pathways from reaching equilibrium

y An analogy for cellularrespiration:

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ATP powers cellular work by coupling exergonic reactions to endergonic reactions

y A cell does three main kinds of work Mechanical- such as the beating of cilia Transport- pumping of substances across membranes C

hemical-

the pushing of endergonic reactionsy Energy coupling- the use of an exergonic reaction to drive an endergonic oneThe Structure and Hydrolysis ofATP

y ATP (adenosine triphosphate)- cells energy shuttle, provides energy for cellularfunctions

y Energy is released from ATP when the terminal phosphate bond is broken:

y ATP hydrolysis can be coupled to other reactions:

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How ATP Performs Work

y ATP drives endergonic reactions by phosphorylation, transferring a phosphate to othermolecules

y The three types of cellular work are powered by the hydrolysis of ATP:

The Regeneration ofATP

y Catabolic pathways drive the regeneration of ATP from ADP and phosphate:

Enzymes speed up metabolic reactions by lowering energy barriers

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y A catalyst is a chemical agent that speeds up a reaction without being consumed by thereaction

y An enzyme is a catalytic proteinThe Activation Barrier

yEvery chemical reaction between molecules involves both bond breaking and bondforming

y The activation energy, EA, or free energy of activation- energy required to contort thereactant molecules so the bonds can change, its supplied in form of heat from

surroundings

y The energy profile for an exergonic reaction:

How Enzymes Lower the EA Barrier

y An enzyme catalyzes reactions by lowering the EA barriery The effect of enzymes on reaction rate:

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Substrate Specificity of Enzymes

y Substrate- reactant an enzyme acts ony enzyme-substrate complex formed when the enzyme binds to its substratey A

ctive site-

region on the enzyme where the substrate binds(a)

y Induced fit of a substrate- brings chemical groups of the active site into positions thatenhance their ability to catalyze the chemical reaction(b)

Catalysis in the Enzymes Active Site

y The catalytic cycle of an enzyme:

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y The active site can lower an EA barrier by:o Orienting substrates correctlyo Straining substrate bondso Providing a favorable microenvironmento C

ovalently bonding to the substrateEffects of Local Conditions on Enzyme Activity

Effects of Temperature and pH

y Each enzyme has an optimal temperature in which it can function:

y And an optimal pH in which it can function:

y Cofactors- nonprotein enzyme helpersy Coenzymes- organic cofactors

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y Competitive inhibitors bind to the active site of an enzyme, competing with thesubstrate:

y Noncompetitive inhibitors bind to another part of an enzyme, changing the function

Regulation of enzyme activity helps control metabolism

Allosteric Regulation of Enzymes

y Allosteric regulation- term used to describe any case in which a proteins function atone site is affected by binding of a regulatory molecule at another site

y Most allosterically regulated enzymes are constructed from one or more polypeptidechains

y They change shape when regulatory molecules bind to specific sites, affecting function

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y Cooperativity- a form of allosteric regulation that can amplify enzyme activity

y Feedback inhibition- The end product of a metabolic pathway shuts down the pathway