Chapter 13 Bioenergetics and Biochemical Reaction Types Flashcards
First Law of Thermodynamics
Conservation of energy: For any physical or chemical change, the total amount of energy in the universe remains constant; energy may change from one form or it may be transported from one region to another, but it cannot be created or destroyed.
Second Law of Thermodynamics
The universe always tends toward increasing disorder: in all natural processes, the entropy of the universe increases.
1) Explain how defining “System” and “Surroundings” allows living organisms to operate within the second law of thermodynamics
First, the second law of thermodynamics states that the universe is constantly moving towards disorder. Organisms (system) work within the 2nd law by exchanging matter and energy with the environment (surroundings) This exchange allows organisms to create order within themselves while also working within the 2nd law of thermodynamics.
Gibbs Free energy
G; expresses the amount of an energy capable of doing work during a reaction at constant temperature and pressure; -∆G spontaneous and exothermic; +∆G non spontaneous and endergonic.
Enthalpy
H; the heat content of the reacting system. It reflects the number and kinds of chemical bonds in the reactants and products
Entropy
S; a quantitative expression for the randomness or disorder in a system.
- From where do cells acquire their necessary free energy? Why can’t cells use heat as a free energy source?
Cells are isothermal. They work at constant, for the most part temperature. Heat cannot of itself pass from one body to a hotter body. Cells acquire their energy from nutrient molecules (heterotrophs), while others obtain energy from the sun (autotrophs)
4. What exactly does “at equilibrium” mean in terms of (a) the rate of both the forward and reverse reactions and (b) the concentrations of the reactants and products?
(a) the rates of the forward and backwards reactions are equal (b) the concentration of the reactants and products are equal and there is no net change
5. What reaction conditions are used to measure the standard free-energy change?
1M, 298˚K, 1 atm, pH 7.
- If, at equilibrium, the concentration of products is greater than reactants is ∆G positive or negative? What can you say about the value of K’eq?
∆G is positive and K’eq
Energy required to break a bond
+∆H
Energy released during bond formation
-∆H
What determines the strength of a bond?
1) Relative electronegativity 2) distance from an elecrons nuclei 3) number of electrons shared 4) nuclear charge
Standard free energy change
∆G’˚ and K’eq. Physical constraints and constants for specific reactions. ∆G’˚ = - RTlnK’eq; this is simply an alternative mathematical way of expressing its equilibrium constant. The standard free energy change tells us in which direction and how far a reaction must go to reach equilibrium at the standard condtions
When K’eq is > 1.0
∆G’˚ is negative and the reaction proceeds forward
When K’eq = 1.0
∆G’˚ is zero and the reaction is at equilibrium
When K’eq is
∆G’˚ is positive and the reaction proceeds in the reverse direction.
Calculations of new version of ∆G to describe the energy of reactions performed at standard conditions: ∆G’˚
∆G = ∆G’˚ + RT ln[products/reactants**] This is the actual conditions. NOT the K’eq!
- What effect does the presence of an enzyme have on the ∆G’˚ that is catalyzes?
Enzymes DO NOT have an effect on constants ∆G˚’. Enzymes do not alter the free energy of a reaction. Enzymes only lower the activation energy by providing an alternative reaction pathway with lower activation energy than the uncatalyzed reaction.
- Under what circumstances can ∆G be negative if ∆G’˚ is positive? Could cells use this strategy to drive thermodynamically unfavorable reactions?
If the term RT ln (p/r) is negative and has a larger absolute value than ∆G˚’. This can occur if the ratio of products to reactants is low.
- Does the value of ∆G˚’ or ∆G tell you anything about (a) the rate at which a reaction occurs or (b) the pathway by which the final product is formed?
(a) ∆G˚’ is a constant and tells us direction ∆G tells us the direction as well, but not specifically the rate. Neither tell the pathway
What is ∆G˚’?
∆G˚’ is the difference between the free-energy content of the products and the free-energy of the reactants under standard conditions. When ∆G˚’ is negative, the products contain less free energy than the reactants and the reaction will proceed spontaneously under standard conditions.
What is the difference between ∆G˚’ and ∆G?
∆G˚’ is a constant. It is unchanging for each reaction. ∆G is not a constant, and does not occur at standard conditions.
Q # 10 How can the coupling of a thermodynamically unfavorable reaction to a thermodynamically favorable reaction increase the K’eq of the overall equation?
∆G˚’ are additive. An exergonic reaction can be added to an endergonic one to produce an energetically favorable reaction. K’eq (equilibrium constants) are multiplicative.
11 Explain why relatively small changes ∆G’˚ correspond to large changes in K’eq.
Because the relationship between K’eq and ∆G˚’ are exponential.
