Energetics of Life and Thermodynamics (chapter 3)

Flashcards covering the energetics of life, laws of thermodynamics, equilibrium, entropy, Gibbs free energy, ATP, and biochemical redox reactions.

What is the primary energy currency with a central role in energy transformations in living organisms?

ATP

What type of thermodynamic system are living organisms classified as?

Open systems

What is generally considered the only truly isolated system in existence?

The entire universe

What is the fundamental principle of the First Law of Thermodynamics?

Conservation of energy

According to the First Law of Thermodynamics, what does DE=q + w represent for open or closed systems?

Conservation of energy

When heat (q) is measured at constant pressure, what thermodynamic quantity is it mathematically equal to?

DH (change in total energy content of the system)

What defines a thermodynamic state function like DH or DE?

Their values depend only on the initial and final states of the system, not the path taken.

Are heat (q) and work (w) considered thermodynamic state functions individually?

No, but their sum (DE) is.

Does the First Law of Thermodynamics provide information about the direction in which energy transformations proceed?

No, it only tracks energy transformations.

What are the two major characteristics of a system at equilibrium?

Forward and reverse rates are equal, and the system is at its lowest possible energy state.

What characterizes systems that are far from equilibrium regarding driving forces?

They have a very strong driving force sending them towards equilibrium.

Where do irreversible changes begin relative to equilibrium?

Far from equilibrium

Where do most biochemical reactions operate relative to equilibrium?

Very near equilibrium

Besides the tendency for loss of energy, what is the second critical factor determining the directionality of changes?

Entropy (S)

What is one interpretation of entropy (S)?

A measure of the randomness or disorder of a system, or whether a system is in its statistically most likely state.

As sucrose diffuses through a solution, what happens to the entropy of the solution?

It increases.

What does the Second Law of Thermodynamics state about the entropy of an isolated system?

The entropy of an isolated system increases.

How is the Second Law of Thermodynamics often interpreted in terms of the universe's entropy?

The entropy of the universe (DSuniv) is greater than 0.

How can the change in entropy of the universe be expressed in terms of the system and surroundings?

DSuniv = DSsys + DSsurr > 0

How is Gibbs Free Energy Change (DG) related to the change in entropy of the universe (DSuniv)?

DG = -TDSuniv

What does a negative value for Gibbs Free Energy Change (DG < 0) indicate about a process?

The process is exergonic and spontaneous.

What does a positive value for Gibbs Free Energy Change (DG > 0) indicate about a process?

The process is endergonic and nonspontaneous.

What factors determine the sign of the Gibbs Free Energy Change (DG)?

DHsys, DSsys, and Temperature (T).

What does a Gibbs Free Energy Change (DG) of zero indicate about a system?

The system is at equilibrium.

Can the entropy of an open system be negative (DS < 0)?

Yes, as long as the entropy of the surroundings (DSsurr) is positive and larger in magnitude.

What is 'free energy' in a system?

The amount of energy available to do useful work.

Can systems at equilibrium do useful work?

No, because DG = 0 at equilibrium.

What does it mean if the reaction quotient (Q) equals the equilibrium constant (K)?

The reaction is at equilibrium.

What principle describes how a reaction will proceed if it is not at equilibrium (Q≠K)?

LeChatelier’s principle, where it will run forward or backward until it reaches equilibrium.

What is the standard free energy change (DG°)?

The change in free energy in going from a standard state (e.g., all reactants and products at 1 M concentration) to equilibrium.

Is the standard free energy change (DG°) a variable or a constant?

It is a constant.

What is the equation that relates the actual free energy change (DG) to the standard free energy change (DG°)?

DG = DG° + RTlnQ

What is the key difference between actual free energy change (DG) and standard free energy change (DG°)?

DG is a variable that depends on starting conditions, while DG° is a constant for a given reaction.

What does DG° (standard free energy change) indicate about a reaction?

The inherent tendency of a reaction to favor one side of the reaction over the other.

What is the difference between homeostasis (steady state) and equilibrium in the context of living cells?

Homeostasis means conditions are relatively constant, often near but not at equilibrium, whereas equilibrium (DG=0) means no useful work can be done, characterizing death.

How can a reaction be kept away from equilibrium in a cell?

By constantly consuming products to keep their concentrations below equilibrium, or constantly keeping reactant concentrations above their equilibrium values (keeping Q<K).

Besides maintaining Q<K, what is another way to drive thermodynamically unfavorable reactions forward?

By thermodynamically coupling them to favorable reactions.

What is an additional criterion for the standard state in biochemical systems (designated DG°’)?

pH=7 ([H+]=1x10-7 M).

How do many biochemical reactions that are endergonic when considered in isolation proceed in a cell?

Through thermodynamic coupling to other reactions.

What often serves as a common component that allows two biochemical reactions to be thermodynamically coupled?

Phosphate.

How is ATP described in the context of cellular energy transactions?

As a major form for energy transactions, or the energy 'currency'.

What characteristic of ATP's phosphoanhydride bonds makes it suitable for driving reactions?

Their hydrolysis is considerably more exergonic than hydrolysis of phosphoester bonds.

How does ATP hydrolysis make the endergonic production of glucose-6-phosphate thermodynamically favorable?

By coupling, the free energy changes are added, resulting in a net negative DG.

How do cells typically regenerate ATP after it has been used?

By coupling ATP synthesis (the reverse of ATP hydrolysis) to the hydrolysis of other compounds.

Besides chemical bonds, where else can free energy be stored in a biological system?

In concentration gradients.

How can a concentration gradient be utilized to drive an endergonic reaction like ATP synthesis?

The spontaneous diffusion of substances from high to low concentration (an exergonic physical process) can be coupled to it.

What does the standard reduction potential (E°’) measure?

The tendency for substances to undergo reduction.

What does a positive standard reduction potential (E°’) indicate about a substance?

It strongly prefers to be reduced.

What does a negative standard reduction potential (E°’) indicate about a substance?

It strongly prefers to be oxidized.

What is the relationship between the standard Gibbs free energy change (DG°’) and the standard reduction potential change (DE°’) for a redox reaction?

DG°’ = -nFDE°’.

What type of redox reactions are thermodynamically favorable based on the standard reduction potential change (DE°’)?

Reactions where DE°’ > 0.

In what form can free energy be stored, related to charge gradients?

As a charge gradient, or an electric field.

What type of gradient drives the regeneration of ATP from ADP by the ATP synthase complex?

A proton chemical gradient.