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From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press - 열역학 : 물질내의 물리적 화학적 변화를 동반하는 에너지변환을 연구하는 학문 - 생체에너지론 : 생물체내 에너지변환을 연구 - 생화학반응의 3 가지 중요한 인자 : 엔탈피 ( 총 열함량 ), 엔트로피 ( 무질서 ), 자유에너지 ( 화학적 일을 하는데 이용할 수 있는 에너지 ) - 자유에너지 : 화학반응의 자발성을 가름함 4.1 열역학 - 제 1 법칙 : 우주의 총 에너지는 일정, 단지 한 형태에서 다른 형태로 전환될 수 있다. - 제 2 법칙 : 우주의 무질서가 증가함, 화학반응은 무질서도가 증가하는 방향으로 -3 법칙 : 완전한 결정고체의 온도가 절대온도 영도 (0K) 에 근접할 때 무질서도는 0 에 근접하게 된다. -1,2 법칙은 생물계내의 에너지변환에 사용 - 우주 ( 시스템과 주위 ) 에서 열과 에너지변환 - 시스템 ? 열린 시스템 : 물질과 에너지는 시스템과 주위 사이에 교환됨 닫힌 시스템 : 에너지만 교환 - 글루코스분자의 에너지함량은 같다 : 일과 열로 변환
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Chapter 4 Section 4.1: Section 4.1: Thermodynamics Section 4.2: Section 4.2: Free Energy Section 4.3: Section 4.3: The Role of ATP Energy Overview From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.1: Thermodynamics Energy is the basic constituent of the universe Energy is the capacity to do work In living organisms, work is powered with the energy provided by ATP Thermodynamics is the study of energy transformations that accompany physical and chemical changes in matter Bioenergetics is the branch that deals with living organisms From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.1: Thermodynamics Three laws of thermodynamics: First Law of Thermodynamics—Energy cannot be created nor destroyed, but can be transformed Second Law of Thermodynamics—Disorder always increases Third Law of Thermodynamics—As the temperature of a perfect crystalline solid approaches absolute zero, disorder approaches zero From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.1: Thermodynamics Bioenergetics is especially important in understanding biochemical reactions These reactions are affected by three factors: Enthalpy—total heat content Entropy—state of disorder Free Energy—energy available to do chemical work From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.1: Thermodynamics First two laws are powerful biochemical tools Thermodynamic transformations take place in a universe composed of a system and its surroundings Energy exchange between a system and its surroundings can happen in two ways: heat (q) or work (w) Work is the displacement or movement of an object by force Figure 4.1 A Thermodynamic Universe From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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(1) 제 1 법칙 -ΔE = q + w ( 시스템의 에너지변화 = 주위로부터 시스템에 의해 흡수된 에너지 + 주위에 의해 시스템에 행해진 일 ) -( 화학자 ) H= E + PV ( 엔탈피 = 압력 - 부피일 ) -ΔH = ΔE ( 일정한 압력의 생화학반응에서 ): 생물계의 총에너지의 변화가 시스템에 의해 방출 혹은 흡수된 에너지와 같음 -ΔH 0, 흡열반응 -ΔH 반응 = ΣΔH 생성물 – ΣΔH 반응물 - 문제 4.1-2 -(2) 제 2 법칙 - 반응이 일어나는지의 예측, 자발적인지 ? - 모든 자발적인 반응과정은 우주의 총 질서를 증가시키는 방향으로 일어난다 ( 그림 4.2) - 휘발유연소시 탄소원자들이 무작위로 분산된다 ( 그림 4.3) - 엔트로피 (S): 자발적인 반응에 대해 양성
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Section 4.1: Thermodynamics First Law of Thermodynamics Expresses the relationship between internal energy (E) in a closed system and heat (q) and work (w) Total energy of a closed system (e.g., our universe) is constant E = q + w Unlike a human body, which is an open system Enthalpy (H) is related to internal energy by the equation: H = E + PV H is often equal to E ( H = E) From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.1: Thermodynamics First Law of Thermodynamics Continued If H is negative ( H <0) the reaction gives off heat: exothermic If is H positive ( H >0) the reaction takes in heat from its surroundings: endothermic In isothermic reactions ( H =0) no heat is exchanged Reaction enthalpy can also be calculated: H reaction = H products H reactants Standard enthalpy of formation per mole (25°C, 1 atm) is symbolized by H f ° From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.1: Thermodynamics As a result of spontaneous processes, matter and energy become more disorganized Gasoline combustion The degree of disorder is measured by the state function entropy (S) Figure 4.3 Gasoline Combustion From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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4.2 자유에너지 - 엔트로피측정의 불가능, 자유에너지를 유도 -ΔS= ΔS 주위 + ΔS 시스템 -ΔS 주위 는 특정 화학적 또는 물리적 변화가 일어나는 동안 K 온도에 대해 교환된 열의 양 : = -ΔH/T - -T ΔS 우주 = ΔH - T ΔS 시스템 --T ΔS 우주 는 깁스자유에너지변화 또는 ΔG 라 함 -ΔG= ΔH - T ΔS - 그림 4.4: 자유에너지 변화는 ΔS 우주가 양성일 때 음성인데, 이는 자발적인 반응이 자유에너지감소 (exergonic) 반응임을 나타낸다. -ΔG=0 면 그 반응은 평형상태임 (1) 표준자유에너지 - 표준자유에너지 ΔG 0 는 용질 1.0M 농도, 1.0 기압, 25 0 C 에서 일어나는 반응 - 자유에너지변화는 반응의 평형상수와 관련 ( 정반응과 역반응의 반응속도가 동일할 때 ) - 평형상태 (ΔG=0) 에서 ΔG 0 = -RTlnKeq -Keq 를 알면 ΔG 0 계산가능 -ΔG 0 ’: 대부분 생화학반응은 pH7.0 부근에서 일어나고, 생체에너지론에서 1M 용질표준에서 일어나므로 이같이 표기 - 문제 4.3
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Section 4.1: Thermodynamics Second Law of Thermodynamics Physical or chemical changes resulting in a release of energy are spontaneous Nonspontaneous reactions require constant energy input All spontaneous processes occur in the direction that increases disorder Figure 4.2 A Living Cell as a Thermodynamic System From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.1: Thermodynamics Second Law of Thermodynamics Continued Entropy change for the universe is positive for every spontaneous process S univ = S sys + S surr Living systems do not increase internal disorder; they increase the entropy of their surroundings For example, food consumed by animals to provide energy and structural materials needed are converted to disordered waste products (i.e., CO 2, H 2 O and heat) Organisms with a S univ = 0 or equilibrium are dead From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.2: Free Energy Free energy is the most definitive way to predict spontaneity Gibbs free energy change or G Negative G indicates spontaneous and exergonic Positive G indicates nonspontaneous and endergonic When G is zero, it indicates a process at equilibrium Figure 4.4 The Gibbs Free Energy Equation From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.2: Free Energy Standard Free Energy Changes Standard free energy, G°, is defined for reactions at 25°C,1 atm, and 1.0 M concentration of solutes Standard free energy change is related to the reactions equilibrium constant, K eq G° = -RT ln K eq Allows calculation of G° if K eq is known Because most biochemical reactions take place at or near pH 7.0 ([H + ] = 1.0 10 -7 M), this exception can be made in the 1.0 M solute rule in bioenergetics The free energy change is expressed as G°′ From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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(2) 짝지어진반응 ( 연관반응 ) - 화학반응에서 자유에너지 값은 연속반응에서 덧셈이 가능 ( 문제 4.4-5) - 그림 4.5 은 연관반응의 예 : 부분적으로는 가능하지 않지만 (3) 소수성효과의 재검토 4.3 ATP 의 역할 -ATP 의 가수분해로 자유에너지제공 ( 그림 4.6) -ATP 의합성 : ADP 와 Pi( 오로토인산 또는 무기인산 ) 로부터 합성 ( 그림 4.7) -ATP 는 아데닌, 리보오스, 삼인산으로 구성된 뉴클레오티드임 ( 그림 4.8) 두 개의 말단 인산기 (PO 4 2- ) 는 무수인산결합 -ATP 가수분해, 인산기 전이전위 : 생체 내 전이 ( 표 4.1) - 포스포엔올피루브산과 비슷한 전이전위 ( 그림 4.9) - 무수인산결합 : 높은 에너지 - 왜 ATP 가수분해가 자유에너지감소반응인가 ?(115 페이지 ) ( 그림 4.10) ( 읽을거리 : 심해의 산화환원 - 에너지생성메카니즘, 무기반응에 의한 에너지획득 - 리토트롭 등 - 질소화박테리아, 유황박테리아 (H 2 S 의 산화 ))
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Coupled Reactions Many reactions have a positive G°′ Free energy values are additive in a reaction sequence If a net G°′ is sufficiently negative, forming the product(s) is an exergonic process Figure 4.5 A Coupled Reaction Section 4.2: Free Energy From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Conversion of glucose-6-phosphate to fructose-1,6- bisphosphate First step is endergonic ( G°′ = +1.7 kJ/mol) so the reaction should not proceed Figure 4.5 A Coupled Reaction Section 4.2: Free Energy From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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The second reaction is exergonic ( G°′ = -14.2 kJ/mol) due to cleavage of ATP’s phosphoanhydride bond The overall G°′ for the coupled reactions is negative ( G°′ = -12.5 kJ/mol); therefore, the reaction does proceed in the direction written at standard conditions Figure 4.5 A Coupled Reaction Section 4.2: Free Energy From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.2: Free Energy The Hydrophobic Effect Revisited Understanding the spontaneous aggregation of nonpolar substances is enhanced by understanding thermodynamic principles The aggregation decreases the surface area of their contact with water, increasing its entropy The free energy of the process is negative; therefore, it proceeds spontaneously Spontaneous exclusion of water is important in membrane formation and protein folding From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Adenosine triphosphate is a nucleotide that plays an extraordinarily important role in living cells Hydrolysis of ATP ADP + P i provides free energy Figure 4.6 Hydrolysis of ATP Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Drives reactions of several types: 1. Biosynthesis of biomolecules 2. Active transport across membranes 3. Mechanical work such as muscle contraction Figure 4.7 The Role of ATP Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Structure of ATP is ideally suited for its role as universal energy currency Its two terminal phosphoryl groups are linked by phosphoanhydride bonds Specific enzymes facilitate ATP hydrolysis Figure 4.8 Structure of ATP Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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The tendency of ATP to undergo hydrolysis is an example of its phosphoryl group transfer potential ATP acts as energy currency, because it can carry phosphoryl groups from high-energy compounds to low-energy compounds Figure 4.9 Transfer of Phosphoryl Groups Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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Several factors need to be considered to understand why ATP is so exergonic: 1. At physiological pH, ATP has multiple negative charges Figure 4.10 Contributing Structure of the Resonance Hybrid of Phosphate Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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2. Because of resonance stabilization, the products of ATP hydrolysis are more stable than resonance- restricted ATP Resonance is when a molecule has two or more alternative structures that differ only in the position of their electrons Figure 4.10 Contributing Structure of the Resonance Hybrid of Phosphate Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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3. Hydrolysis products of ATP are more easily solvated 4. Increase in disorder with more molecules Section 4.3: The Role of ATP From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press
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