Biochemistry Standard Reduction Potentials Quiz

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Questions and Answers

Which half-reaction has the highest standard reduction potential among the given reactions?

Fe3+ + e-  Fe2+

Cytochrome a3 (Fe3+) + e-  Cyt a3 (Fe2+)

NADP+ + 2H+ + 2e-  NADPH + H+

1/2O2 + 2H+ + 2e-  H2O (correct)

What is the standard reduction potential of the reaction involving fumarate and succinate?

0.031 V (correct)

0.295 V

-0.220 V

-0.031 V

If a reaction has a ΔG°′ of +3.0 Kcal/mole, what can be inferred about its spontaneity under standard conditions?

The reaction is at equilibrium.

The reaction will proceed to completion.

The reaction is non-spontaneous. (correct)

The reaction is spontaneous.

In the reaction ATP + Pyruvate ⇌ Phosphoenolpyruvate + ADP, if the ratio of ATP to ADP is 10, what does that suggest about the equilibrium concentration of pyruvate relative to PEP?

Greater concentration of PEP than pyruvate. Signup and view all the answers

Which of the following half-reactions shows the most negative standard reduction potential?

Ferrodoxin (Fe3+) + e-  Ferdx (Fe2+) Signup and view all the answers

What is the standard reduction potential for the half-reaction involving cytochrome c1?

0.220 V Signup and view all the answers

What is the ΔG' for the reaction ATP + Cr ⇌ CrP + ADP based on the given data?

+3.0 Kcal/mole Signup and view all the answers

What does Eo' represent in relation to a half-cell reaction?

The potential at which the oxidized and reduced forms are equal Signup and view all the answers

Which of the following correctly describes the relationship between Eo' and the spontaneity of a redox reaction?

A reaction is spontaneous if Eo' of the donor is more negative than that of the acceptor Signup and view all the answers

In the context of electron transfer reactions, what does the term 'reducing agent' refer to?

The species that loses electrons Signup and view all the answers

Which equation correctly represents the relationship between free energy change and electrode potential?

ΔG' = -nFΔE' Signup and view all the answers

What indicates a spontaneous electron transfer reaction according to the Nernst equation?

ΔE' > 0 Signup and view all the answers

What occurs during the reaction Aox + Bred ⇌ Ared + Box?

Box acts as the oxidizing agent Signup and view all the answers

Which term best describes the reaction, where E' = Eo' when [Ared] = [Aox]?

Equilibrium condition Signup and view all the answers

What is the significance of the variable 'n' in the equation E' = Eo' - RT/nF Ln([reduced]/[oxidized])?

It denotes the number of electrons transferred Signup and view all the answers

What is true about the relationship between the reduced and oxidized forms in a redox reaction?

Both forms can coexist at equal concentrations under standard conditions Signup and view all the answers

What is the primary significance of a kilocalorie (Kcal) in energy measurements?

It is equal to 1000 calories and represents a larger unit of energy. Signup and view all the answers

How is the relationship between $ riangle G'o$ and $K'e$ characterized?

They are inversely related. Signup and view all the answers

What is the calculated free energy change ($ riangle G'$) in the second example when given specific concentrations of DHAP and GAL-3-P?

-0.7 Kcal/mole Signup and view all the answers

At standard conditions, what is the value of $ riangle G'o$ when $K'e = 1$?

0 Kcal/mole Signup and view all the answers

Which of the following statements best describes coupled reactions in biochemistry?

A spontaneous reaction can drive a non-spontaneous reaction, making the overall process favorable. Signup and view all the answers

What temperature and pH conditions were used in the first example for considering the equilibrium constant $K'e$?

25°C and pH 7 Signup and view all the answers

How does the term 'kinetically facilitated' apply to enzyme-catalyzed coupled reactions?

It indicates that the individual reactions are accelerated while ensuring they remain separate. Signup and view all the answers

What is the logarithmic relationship used to compute $ riangle G'o$ with $K'e$?

$ riangle G'o = -2.303 RT ext{Log}(K'e)$ Signup and view all the answers

When the concentrations of [DHAP] and [GAL-3-P] are adjusted, how does this affect spontaneity?

Adjustments of these concentrations can influence whether the reaction becomes spontaneous. Signup and view all the answers

What is bioenergetics primarily concerned with?

The quantitative study of energy transductions in living cells Signup and view all the answers

Which of the following energy transformations is NOT typically associated with living organisms?

Converting sound energy into kinetic energy Signup and view all the answers

How do living organisms utilize the energy they extract?

For biosynthesis, transport, and motility Signup and view all the answers

What fundamental ability is essential for living organisms in relation to energy?

To harness and channel energy for biological work Signup and view all the answers

What are the two crucial questions in biochemistry regarding energy?

How do organisms extract energy from their surroundings? How do they use this energy for survival? Signup and view all the answers

Which of the following best describes an energy transduction process in living systems?

Conversion of energy stored in nutrients to mechanical work Signup and view all the answers

Which type of organisms primarily transduce light energy into other forms of energy?

Photosynthetic organisms Signup and view all the answers

What is a key aspect of the thermodynamics of biological reactions?

They obey the laws of thermodynamics while converting energy forms Signup and view all the answers

What does a negative value of ΔG indicate about a biochemical reaction?

The reaction is spontaneous. Signup and view all the answers

In the equation ΔG = ΔE - TΔS, what role does TΔS play?

It represents the change in entropy. Signup and view all the answers

What is the relationship between standard free-energy change and the equilibrium constant?

They are inversely proportional. Signup and view all the answers

What value does ΔG have at equilibrium for a reversible biochemical reaction?

ΔG = 0 Signup and view all the answers

What is indicated by a ΔG° value of -686 Kcal/mol for the reaction of glucose and oxygen?

The reaction is exergonic and releases energy. Signup and view all the answers

Which condition is usually assumed for deriving thermodynamic terms in chemistry?

A pH of 0.0. Signup and view all the answers

What does Ke represent in the equation ΔG° = -RT Ln Ke?

The equilibrium constant. Signup and view all the answers

Which of the following statements about free energy is true?

ΔG° represents changes under standard conditions. Signup and view all the answers

What is the primary significance of ΔG′ and ΔG′° in biochemical contexts?

To differentiate biochemical reactions from chemical ones under physiological conditions. Signup and view all the answers

How are the values of R and T applied in the equation for ΔG°?

R is the gas constant, and T is absolute temperature. Signup and view all the answers

Study Notes

Principles of Bioenergetics

Living cells and organisms must perform work to stay alive, grow, and reproduce.
The ability to harness and channel energy into biological work is a fundamental property of all living organisms. This ability evolved early in cellular development.
Modern organisms exhibit a wide variety of energy conversions and transductions.
Organisms use the chemical energy in fuels to synthesize complex macromolecules from simple precursors.
Organisms can convert fuel chemical energy into concentration gradients, electrical gradients, motion, heat, and, in some cases, light.
Photosynthetic organisms convert light energy into other energy forms.

Lecture Considerations

The nature of biological energy transformations
Thermodynamics of biological reactions
How living organisms extract energy from their surroundings
How organisms use this energy for biosynthesis, transport, and motility (survival).

Bioenergetics Definition

Bioenergetics is the quantitative study of energy transductions in living cells. This includes changes in one form of energy into another.
Bioenergetics also focuses on the chemical processes underlying these transductions.
Biological energy transformations adhere to thermodynamic laws.

First Law of Thermodynamics

The principle of energy conservation states the total energy of a closed system remains constant.
Energy can change form or be moved from one region to another but can't be created or destroyed.
Energy changes are independent of the path of transformation. The difference in energy between initial and final states is constant.

Second Law of Thermodynamics

The universe tends towards increasing disorder in all natural processes, meaning entropy increases.
The sum of the entropy differences of the system and surroundings is greater than zero for a spontaneous reaction.

Reacting Systems and the Universe

The reacting system is the collection of matter undergoing a chemical or physical process (cell, organism, reactants).
The system and its surroundings together constitute the universe.
In a laboratory, some reactions occur in isolated or closed systems (no material or energy exchange with surroundings).
Living organisms have open systems, constantly exchanging matter and energy with their surroundings. However, they never reach equilibrium. These constant transactions allow organisms to create order while following the second law of thermodynamics.

Two Groups of Organisms

Chemotrophs: Use fuel molecules (carbohydrates, fats, proteins) to obtain chemical energy
Phototrophs: Convert radiant energy (photons) from sunlight into chemically useful energy.

Free Energy

Gibbs free energy (G) quantifies the amount of energy for work during a constant temperature and pressure reaction.
Enthalpy (H) is the heat content of a reacting system, reflecting the chemical bonds in reactants and products. Exothermic reactions release heat; endothermic reactions absorb heat, with enthalpy changes having conventional negative or positive values, respectively.
Entropy (S) is the quantitative measure of a system's order or disorder.

Free Energy & Equilibrium Constant

Free energy (ΔG) is related to the equilibrium constant (K). A negative ΔG indicates a spontaneous reaction (exergonic).
Positive ΔG signifies a non-spontaneous one (endergonic).
At equilibrium, ΔG = 0
Standard free energy changes (ΔG°) are directly connected to equilibrium constants (K₂) under standard conditions (298K or 25°C)

Relationship between ΔG° and Ke

ΔGº and Ke are inversely related. If ΔGº' is negative, then K' e is positive

Coupled Reactions

Unfavorable reactions can become favourable when coupled to a more favorable one.
Free energy changes of coupled reactions are additive.
Enzymes can facilitate coupled reaction by bringing reactants close together in their active site, which prevents individual reactions.

Redox Reactions

Organisms acquire energy from redox reactions.
Redox happens when one reactant gets oxidized and one gets reduced. This involves electron transfer.
Oxidized and reduced forms of molecules have specified half-reactions and potentials.
The standard reduction potential (E°) is the potential for each half-reaction that is measured against the hydrogen half-reaction.

Problems

Example problems and solutions on determining ∆G
- Calculation of ΔG (and K), using data given. These problems may involve isomerization and ATP coupling.

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Description

Test your knowledge on standard reduction potentials and Gibbs free energy relationships in biochemical reactions. This quiz covers half-reactions, equilibrium concentrations, and the role of reducing agents. Perfect for students studying biochemistry and cellular metabolism.