Comprehensive Study Guidance for BMS247 Human Biochemistry Exam

Q1. Reciprocal regulation refers to:

Background

Topic: Regulation of Metabolic Pathways

This question tests your understanding of how cells control opposing metabolic pathways, such as glycolysis and gluconeogenesis, to avoid futile cycles and maintain metabolic balance.

Key Terms:

• Reciprocal regulation: The process by which one pathway is activated while the opposing pathway is suppressed.

• Anabolic pathway: Builds molecules and usually requires energy.

• Catabolic pathway: Breaks down molecules and usually releases energy.

Step-by-Step Guidance

1. Consider how cells prevent simultaneous activation of opposing pathways (e.g., glycolysis vs. gluconeogenesis).

2. Think about the role of allosteric regulation and hormonal signals in controlling these pathways.

3. Identify which answer choices describe activation of one pathway and suppression of the other.

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Q2. If a 0.1 M solution of glucose 1-phosphate at 25°C is incubated with a catalytic amount of phosphoglucomutase, the glucose 1-phosphate is transformed to glucose 6-phosphate. At equilibrium, the concentrations are: Glucose 1-phosphate: $4.5 \times 10^{-3}$ M, Glucose 6-phosphate: $9.6 \times 10^{-2}$ M. Which statement is correct? (R = 8.315 J/mol•K; T = 298 K)

Background

Topic: Thermodynamics of Biochemical Reactions

This question tests your ability to calculate the standard free energy change ($\Delta G'^{\circ}$) using equilibrium concentrations.

Key formula:

$\Delta G'^{\circ} = -RT \ln K'_{eq}$

• $R$ = gas constant ($8.315$ J/mol·K)

• $T$ = temperature in Kelvin ($298$ K)

• $K'_{eq}$ = equilibrium constant ($\frac{[\text{glucose 6-phosphate}]}{[\text{glucose 1-phosphate}]}$)

Step-by-Step Guidance

1. Calculate the equilibrium constant: $K'_{eq} = \frac{9.6 \times 10^{-2}}{4.5 \times 10^{-3}}$

2. Plug $K'_{eq}$, $R$, and $T$ into the formula $\Delta G'^{\circ} = -RT \ln K'_{eq}$

3. Evaluate the sign and magnitude of $\Delta G'^{\circ}$ to determine which answer is correct.

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Q3. The reaction A + B → C has a ΔG'° of -20 KJ/mol at 25°C. Starting under standard conditions, one can predict that:

Background

Topic: Free Energy and Reaction Direction

This question tests your understanding of how the sign and magnitude of $\Delta G'^{\circ}$ relate to equilibrium and product formation.

Key Terms:

• $\Delta G'^{\circ}$: Standard free energy change

• Equilibrium: The point at which the forward and reverse reaction rates are equal

Step-by-Step Guidance

1. Recall that a negative $\Delta G'^{\circ}$ means the reaction is thermodynamically favorable.

2. Consider what happens to the concentrations of reactants and products at equilibrium.

3. Compare the concentration of C to those of A and B based on the direction of the reaction.

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Q4. Which is NOT true about the following reactions? A → B ΔG = +20 kJ/mol (reaction 1), C → D ΔG = –30 kJ/mol (reaction 2), A + C → B + D (reaction 3)

Background

Topic: Coupled Reactions and Free Energy

This question tests your understanding of how reactions can be coupled and how their free energy changes combine.

Key formula:

$\Delta G_{\text{overall}} = \Delta G_1 + \Delta G_2$

• Spontaneity: Negative $\Delta G$ means spontaneous

• Enzyme effect: Enzymes change reaction rate, not equilibrium

Step-by-Step Guidance

1. Calculate the overall $\Delta G$ for reaction 3 by adding the values for reactions 1 and 2.

2. Determine which direction each reaction proceeds spontaneously based on $\Delta G$.

3. Consider the effect of enzymes on equilibrium and reaction rate.

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Q5. Which statement about anabolic reactions is true?

Background

Topic: Anabolic vs. Catabolic Reactions

This question tests your understanding of the characteristics of anabolic reactions, including their energy requirements and role in metabolism.

Key Terms:

• Anabolic reactions: Build complex molecules from simpler ones, usually require energy (endergonic)

• Catabolic reactions: Break down molecules, usually release energy (exergonic)

Step-by-Step Guidance

1. Recall the main features of anabolic reactions (energy requirement, direction, organism type).

2. Compare each answer choice to these features.

3. Identify which statement accurately describes anabolic reactions.

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Q6. What is the standard free energy change (ΔG°) for the hydrolysis of ATP to ADP?

Background

Topic: ATP Hydrolysis and Energy Release

This question tests your knowledge of the energetics of ATP hydrolysis, a fundamental reaction in biochemistry.

Key formula:

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i$

$\Delta G^{\circ}$ for ATP hydrolysis is typically negative, indicating energy release.

Step-by-Step Guidance

1. Recall the typical value for $\Delta G^{\circ}$ of ATP hydrolysis (in kJ/mol).

2. Compare the answer choices to the expected value and sign.

3. Identify which value matches the standard free energy change for ATP hydrolysis.

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Q7. The standard free-energy changes for the reactions below are given: Phosphocreatine → creatine + Pi ΔG'° = –43.0 kJ/mol; ATP → ADP + Pi ΔG'° = –30.5 kJ/mol. What is the overall ΔG'° for the following reaction, which occurs when muscle cells deplete their ATP reserves? Phosphocreatine + ADP → creatine + ATP

Background

Topic: Coupled Reactions and Free Energy Calculations

This question tests your ability to combine standard free energy changes for coupled reactions.

Key formula:

$\Delta G'^{\circ}_{\text{overall}} = \Delta G'^{\circ}_1 + (-\Delta G'^{\circ}_2)$

• Reverse the direction of ATP hydrolysis to ATP synthesis.

Step-by-Step Guidance

1. Write the two reactions and their $\Delta G'^{\circ}$ values.

2. Reverse the ATP hydrolysis reaction to represent ATP synthesis (change the sign).

3. Add the $\Delta G'^{\circ}$ values to find the overall change for the coupled reaction.

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