Bioenergetics

Question 1

The First Law of Thermodynamics states that energy can:

a) Be created from nothing
b) Be destroyed when needed
c) Change forms but the total amount remains constant
d) Be measured only in living systems

Answer 1

c) Change forms but the total amount remains constant

Question 2

Which of the following increases the entropy of a system?
a) Formation of ice from water
b) Dissolving salt in water
c) Solidifying wax
d) Condensation of water vapor

Answer 2

b) Dissolving salt in water

Question 3

A spontaneous biochemical reaction:
a) Has a positive ΔG
b) Has a negative ΔG
c) Always produces heat
d) Requires energy input

Answer 3

b) Has a negative ΔG

Question 4

Which of the following best describes an exergonic reaction?

a) Consumes energy and non-spontaneous
b) Releases energy and spontaneous
c) Has products with higher free energy than reactants
d) Occurs only in anabolic pathways

Answer 4

b) Releases energy and spontaneous

Question 5

The main role of ATP in cells is to:

a) Store genetic information
b) Act as an energy currency to drive endergonic reactions
c) Provide structural support to membranes
d) Function as an enzyme

Answer 5

b) Act as an energy currency to drive endergonic reactions

Question 6

ATP hydrolysis releases energy primarily due to:

a) Breaking of alpha-phosphate ester bond
b) Formation of high-energy beta and gamma phosphoanhydride bonds
c) Products (ADP + Pi) being more stable than ATP
d) Energy released during nucleotide synthesis

Answer 6

c) Products (ADP + Pi) being more stable than ATP

Question 7

Which bond in ATP is NOT considered a high-energy bond?

a) Alpha phosphate
b) Beta phosphate
c) Gamma phosphate
d) Phosphoanhydride bonds

Answer 7

a) Alpha phosphate

Question 8

According to Gibbs free energy equation, when ΔG is zero, the reaction:

a) Proceeds spontaneously forward
b) Proceeds spontaneously backward
c) Is at equilibrium
d) Releases maximal energy

Answer 8

c) Is at equilibrium

Question 9

Which of the following is TRUE regarding coupling of reactions?

a) Endergonic reactions occur independently
b) Exergonic reactions supply energy to drive endergonic ones
c) Endergonic reactions release energy to exergonic reactions
d) Coupling reactions occur only in the liver

Answer 9

b) Exergonic reactions supply energy to drive endergonic ones

Question 10

A high-energy intermediate common to energy coupling in cells is:

a) NAD+
b) ATP
c) Coenzyme A
d) Pyruvate

Answer 10

b) ATP

Question 11

The reaction converting acetyl-CoA to citrate in the Krebs cycle is:

a) Endergonic and reversible
b) Exergonic and irreversible
c) Endergonic and irreversible
d) Exergonic and reversible

Answer 11

b) Exergonic and irreversible

Question 12

The reaction converting acetyl-CoA to citrate in the Krebs cycle is:

a) Endergonic and reversible
b) Exergonic and irreversible
c) Endergonic and irreversible
d) Exergonic and reversible

Answer 12

a) Endergonic and reversible

Question 13

Which of the following statements about ΔG° (standard free energy change) is correct?

a) It varies with cellular conditions such as pH and substrate concentration
b) It is fixed for a reaction under standard conditions
c) It predicts the actual direction of a reaction inside cells
d) It is positive for all spontaneous reactions

Answer 13

b) It is fixed for a reaction under standard conditions

Question 14

The relationship between ΔG° and equilibrium constant (Keq) is:

a) ΔG° = -RT ln Keq
b) ΔG° = RT ln Keq
c) ΔG° = Keq / RT
d) ΔG° = Keq × RT

Answer 14

a) ΔG° = -RT ln Keq

Question 15

Which of the following is NOT an example of substrate-level phosphorylation?

a) ATP formation by phosphoglycerate kinase in glycolysis
b) ATP formation by succinyl-CoA synthetase in TCA cycle
c) ATP synthesis powered by ATP synthase in mitochondria
d) ATP formation by pyruvate kinase in glycolysis

Answer 15

c) ATP synthesis powered by ATP synthase in mitochondria

Question 16

Oxidative phosphorylation differs from substrate-level phosphorylation in that it:

a) Requires direct phosphate transfer from substrate to ADP
b) Utilizes an electron transport chain and proton gradient
c) Occurs only in the cytoplasm
d) Does not require oxygen

Answer 16

b) Utilizes an electron transport chain and proton gradient

Question 17

Which of the following is a major source of ATP in aerobic cells?

a) Glycolysis alone
b) Oxidative phosphorylation
c) Fermentation
d) Fatty acid synthesis

Answer 17

b) Oxidative phosphorylation

Question 18

The second law of thermodynamics states that:
a) Energy can be destroyed
b) Total entropy must decrease for a reaction to be spontaneous
c) Total entropy must increase for a reaction to proceed spontaneously
d) Energy is created in exergonic reactions

Answer 18

c) Total entropy must increase for a reaction to proceed spontaneously

Question 19

In which biochemical pathway is ATP generated by substrate-level phosphorylation?

a) Electron transport chain
b) Citric acid cycle
c) Beta-oxidation
d) Gluconeogenesis

Answer 19

b) Citric acid cycle

Question 20

Which of the following contributes to the high energy stored in ATP’s phosphoanhydride bonds?

a) Electrostatic repulsion among phosphate groups
b) Resonance stabilization of products after hydrolysis
c) Increased solvation of products
d) All of the above

Answer 20

d) All of the above

Question 21

Which thermodynamic parameter changes indicate an unfavorable reaction?

a) Negative ΔH and positive ΔS
b) Positive ΔG
c) Negative ΔG
d) None of the above

Answer 21

b) Positive ΔG

Question 22

Electron carriers in the mitochondrial electron transport chain include:

a) ATP and ADP
b) NAD+/NADH and FAD/FADH2
c) Coenzyme A only
d) Pyruvate and lactate

Answer 22

b) NAD+/NADH and FAD/FADH2

Question 23

Which of the following can increase the spontaneity of a reaction?

a) Increasing temperature for a reaction with positive ΔS
b) Increasing reactant concentrations only
c) Decreasing entropy
d) None of the above

Answer 23

a) Increasing temperature for a reaction with positive ΔS

Question 24

The term “downhill reaction” in biochemical metabolism corresponds to:

a) Endergonic reactions
b) Exergonic reactions
c) Non-spontaneous reactions
d) Energy consuming reactions

Answer 24

b) Exergonic reactions

Question 25

In ATP hydrolysis, which product is associated with pyrophosphate release? a) ADP b) AMP c) Pi d) ATP

Answer 25

b) AMP

Question 26

The hydrolysis of ATP to ADP + Pi under physiological conditions releases approximately: a) +7.3 kcal/mol b) -7.3 kcal/mol c) 0 kcal/mol d) -30 kcal/mol

Answer 26

b) -7.3 kcal/mol

Question 27

Which of the following is a function of heat released during exergonic reactions in the body? a) Maintains normal body temperature b) Drives endergonic processes directly c) Alters entropy negatively d) Destroys cellular proteins

Answer 27

a) Maintains normal body temperature

Question 28

A reaction with ΔG = +5 kcal/mol is: a) Spontaneous b) At equilibrium c) Non-spontaneous and requires energy input d) Exergonic

Answer 28

c) Non-spontaneous and requires energy input

Question 29

Which statement correctly describes the relationship of free energy change (ΔG) and reaction direction? a) When ΔG < 0, reaction proceeds towards reactants b) When ΔG > 0, reaction proceeds spontaneously forward c) When ΔG = 0, reaction is at equilibrium d) ΔG is unrelated to spontaneity

Answer 29

c) When ΔG = 0, reaction is at equilibrium

Question 30

A metabolic pathway has 3 consecutive reactions with ΔG° values of -5, +3, and -1 kcal/mol. The overall ΔG° of the pathway is: a) -3 kcal/mol b) +7 kcal/mol c) -9 kcal/mol d) +1 kcal/mol

Answer 30

a) -3 kcal/mol Sum of ΔG° = -5 + 3 + (-1) = -3 kcal/mol, overall exergonic.

Question 31

A biochemical reaction with a large negative ΔG will: A. Proceed spontaneously and be essentially irreversible B. Require input of energy to proceed C. Be at equilibrium D. Proceed but at a very slow rate

Answer 31

A. Proceed spontaneously and be essentially irreversible

Question 32

The standard free energy change (ΔG⁰′) is measured under which conditions? A. At 37°C, pH 7, and 1 M reactant concentrations B. Any temperature at pH 7 C. At 25°C, with any pH D. When product concentrations equal zero

Answer 32

A. At 37°C, pH 7, and 1 M reactant concentrations

Question 33

Enzymes affect biochemical reactions by: A. Increasing the ΔG⁰′ B. Changing the equilibrium concentrations C. Lowering the activation energy and speeding equilibrium attainment D. Consuming ATP

Answer 33

C. Lowering the activation energy and speeding equilibrium attainment

Question 34

Coupling of an endergonic (energy-consuming) reaction to an exergonic (energy-releasing) reaction in cells enables: A. Endergonic processes to proceed spontaneously B. Exergonic processes to stop completely C. All reactions to become irreversible D. Enzymes to be replaced by ATP

Answer 34

A. Endergonic processes to proceed spontaneously

Question 35

The free energy released on hydrolysis of the terminal phosphate of ATP is large because: A. The P-O bond broken releases energy directly B. ATP products are more stabilized due to resonance and reduced electrostatic repulsion C. ATP is a very unstable molecule only found in cells D. The reaction produces heat only

Answer 35

B. ATP products are more stabilized due to resonance and reduced electrostatic repulsion

Question 36

The term “~P” in biochemical compounds like ATP indicates: A. A phosphate group with low energy of hydrolysis B. A high-energy phosphate bond that transfers free energy efficiently C. A free phosphate ion D. A phosphate group not involved in energy transfer

Answer 36

B. A high-energy phosphate bond that transfers free energy efficiently

Question 37

Which of the following molecules has a higher group transfer potential (releases more free energy on hydrolysis) than ATP? A. Glucose-6-phosphate B. 1,3-Bisphosphoglycerate C. Adenosine monophosphate (AMP) D. Fructose-6-phosphate

Answer 37

B. 1,3-Bisphosphoglycerate 1,3-Bisphosphoglycerate has a more negative ΔG of hydrolysis than ATP, thus higher transfer potential.

Question 38

During muscle contraction, phosphagens like creatine phosphate serve to: A. Store high-energy phosphate groups and rapidly regenerate ATP B. Replace ATP in energy transfer permanently C. Inhibit ATPase activity D. Hydrolyze ATP slowly

Answer 38

A. Store high-energy phosphate groups and rapidly regenerate ATP

Question 39

Which process generates the greatest quantity of ATP in aerobic organisms? A. Aerobic glycolysis B. Oxidative phosphorylation C. Citrate cycle substrate-level phosphorylation D. Creatine phosphate hydrolysis

Answer 39

B. Oxidative phosphorylation

Question 40

In glycolysis, net ATP production per molecule of glucose is: A. 1 ATP B. 2 ATP C. 4 ATP D. 0 ATP

Answer 40

B. 2 ATP

Question 41

The succinate thiokinase step in the citric acid cycle produces: A. NADH B. FADH₂ C. ATP (or GTP) directly by substrate-level phosphorylation D. Carbon dioxide

Answer 41

C. ATP (or GTP) directly by substrate-level phosphorylation

Question 42

ATP hydrolysis can provide energy for several cellular processes. Which of the following is NOT typically powered by ATP hydrolysis? A. Biosynthetic reactions B. Active transport across membranes C. Heat generation during thermogenesis D. Passive diffusion through lipid bilayers

Answer 42

D. Passive diffusion through lipid bilayers

Question 43

The coupling of dehydrogenation (oxidation) and hydrogenation (reduction) reactions in metabolism occurs via: A. Direct electron transfer between substrates B. Intermediate carriers like NAD⁺/NADH C. ATP alone D. Oxygen only

Answer 43

B. Intermediate carriers like NAD⁺/NADH

Question 44

Which statement best summarizes the role of ATP in living cells? A. ATP stores energy long-term like fat reserves B. ATP is continuously recycled and links exergonic and endergonic pathways C. ATP is only produced during glycolysis D. ATP synthesis requires no enzymes

Answer 44

B. ATP is continuously recycled and links exergonic and endergonic pathways

Question 45

A cell’s ATP/ADP pool is: A. Very large, sufficient to maintain metabolic activity for hours without replenishment B. Small and rapidly turned over to maintain energy homeostasis C. Constant regardless of cellular activity D. Synthesized only in the cytoplasm

Answer 45

B. Small and rapidly turned over to maintain energy homeostasis

Question 46

The free energy of hydrolysis of ATP to AMP + PPi is: A. Lower than hydrolysis to ADP + Pi B. Equal to hydrolysis to ADP + Pi C. Greater (more negative) than hydrolysis to ADP + Pi D. Not biologically relevant

Answer 46

C. Greater (more negative) than hydrolysis to ADP + Pi

Question 47

What is the energetic consequence when NADH and FAD(2H) are oxidized by O₂ in the electron transport chain? A. Production of heat only B. Regeneration of ATP by oxidative phosphorylation C. Formation of glucose D. Degradation of proteins

Answer 47

B. Regeneration of ATP by oxidative phosphorylation

Question 48

The maximum quantity of useful energy released during fuel oxidation is called: A. Enthalpy (ΔH) B. Standard free energy change (ΔG₀′) C. Entropy (ΔS) D. Gibbs equilibrium constant

Answer 48

B. Standard free energy change (ΔG₀′)

Question 49

Which of the following reactions is endergonic under standard conditions? A. Hydrolysis of ATP B. Oxidation of glucose C. Synthesis of ATP from ADP and Pi D. Fermentation of lactate

Answer 49

C. Synthesis of ATP from ADP and Pi

Question 50

Which of the following bonds in ATP is classified as a high-energy phosphate bond? A. Adenine-ribose bond B. Phosphoester bond C. Phosphoanhydride bond D. Glycosidic bond

Answer 50

C. Phosphoanhydride bond

Question 51

The large negative ΔG₀′ of ATP hydrolysis is primarily due to: A. Direct heat release B. Higher stability of products via reduced electrostatic repulsion and resonance stabilization C. Increased concentration of ATP in mitochondria D. Decreased enthalpy

Answer 51

B. Higher stability of products via reduced electrostatic repulsion and resonance stabilization

Question 52

The phosphoanhydride bond between which phosphate groups in ATP releases ≈7.3 kcal/mol upon hydrolysis? A. γ and β phosphates B. Adenine and ribose C. First carbon of ribose and α phosphate D. Adenine and β phosphate

Answer 52

A. γ and β phosphates

Question 53

Why is ATP hydrolysis within the cell not usually performed directly to drive a process? A. Heat cannot be converted efficiently into useful work B. ATP is unstable C. Only ADP can be hydrolyzed directly D. Energy is less than required for most reactions

Answer 53

A. Heat cannot be converted efficiently into useful work

Question 54

Which component acts as the final electron acceptor in the electron transport chain? A. NAD⁺ B. Oxygen C. Carbon dioxide D. Ubiquinone

Answer 54

B. Oxygen

Question 55

In the heart, approximately what percent of its ATP content is used with each contraction? A. 10% B. 2% C. 0.1% D. 20%

Answer 55

B. 2%

Question 56

The value −7.3 kcal/mol for ATP hydrolysis represents: A. Energy required for ATP synthesis B. Standard free energy change (ΔG₀′) under defined laboratory conditions C. Actual free energy in all cellular conditions D. The caloric value of glucose oxidation

Answer 56

B. Standard free energy change (ΔG₀′) under defined laboratory conditions

Question 57

A reaction with a positive ΔG₀′: A. Is always spontaneous B. Cannot occur under any condition in the cell C. Can proceed if coupled to a reaction with large negative ΔG₀′ D. Is always an oxidation

Answer 57

C. Can proceed if coupled to a reaction with large negative ΔG₀′

Question 58

TRUE OR FALSE: Entropy becomes maximum as equilibrium is approached

Answer 58

True

Question 59

Among the alpha, beta, and gamma phosphate bond of ATP, which bonds are of higher energy?

Answer 59

Beta and Gamma Bond

Question 60

What are the three major sources of high energy phosphates in energy conservation?

Answer 60

1. Oxidative Phosphorylation 2. Kreb's Cycle (succinate thiokinase) 3. Glycolysis (pyruvate and phosphoglycerate kinase)

Question 61

What manner of ATP synthesis occurs at the phosphoglycerate kinase reaction of glycolysis?

Answer 61

substrate level phosphorylation

Question 62

TRUE OR FALSE: Both ATP synthesis that occurs in glycolysis is a form of substrate level phosphorylation

Answer 62

True

Question 63

In which tissues and organs is creatine kinase found?

Answer 63

Skeletal and cardiac muscles

Question 64

What enzyme converts GDP to ATP in the Krebs Cycle?

Answer 64

nucleotide diphosphate kinase

Question 65

TRUE OR FALSE: A catabolic reaction is an exergonic reaction

Answer 65

True

Question 66

What is the Gibbs equation formula

Answer 66

Energy = heat - temperature (entropy)