③ Metabolism (hard MCQ)

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Questions and Answers

How does the induced fit model refine the lock-and-key model of enzyme-substrate interactions?

It proposes that the active site changes shape slightly upon substrate binding, optimizing the interaction. (correct)
It eliminates the need for specific active sites, allowing enzymes to bind to a wider range of substrates.
It focuses solely on the hydrolysis of substrates, ignoring synthesis reactions.
It suggests that the active site is completely rigid, ensuring only perfectly matching substrates can bind.

Which of the following is the MOST direct outcome of the electron transport chain in cellular respiration?

Pumping of protons across the inner mitochondrial membrane to create an electrochemical gradient. (correct)
Direct production of ATP via substrate-level phosphorylation.
Formation of water by combining electrons with hydrogen ions and oxygen.
Regeneration of NAD+ and FAD for use in glycolysis and the Krebs cycle.

How does photorespiration affect photosynthetic efficiency in plants, and why is it more prevalent in certain environmental conditions?

It decreases efficiency by consuming ATP and oxygen while releasing carbon dioxide, and is favored when carbon dioxide levels are low and oxygen levels are high. (correct)
It increases efficiency by providing additional carbon dioxide for the Calvin cycle, especially in hot, dry conditions.
It has no significant effect on photosynthetic efficiency, as it only occurs under specific laboratory conditions.
It enhances efficiency in cold environments by protecting enzymes from temperature-induced denaturation.

How does competitive inhibition affect the kinetics of an enzyme-catalyzed reaction, and what strategies can overcome this inhibition?

It leaves the $V_{max}$ unchanged but increases the $K_m$, and can be overcome by increasing the substrate concentration. (D) Signup and view all the answers

In the context of cellular respiration, what is the primary role of coenzymes such as NAD+ and FAD, and how are they regenerated after accepting electrons?

They act as electron carriers, accepting electrons during glycolysis and the Krebs cycle, and are regenerated in the electron transport chain. (C) Signup and view all the answers

What is the significance of cyclic electron flow in photosynthesis, and under what conditions is it most likely to occur?

It produces ATP without producing NADPH or releasing oxygen, and occurs when the plant needs additional ATP. (A) Signup and view all the answers

How do allosteric enzymes differ from enzymes with simple Michaelis-Menten kinetics, and what is the physiological importance of this difference?

Allosteric enzymes follow a sigmoidal curve, while Michaelis-Menten enzymes follow a hyperbolic curve, allowing for more sensitive regulation. (A) Signup and view all the answers

What would be the consequence of a mutation that disables the enzyme responsible for converting glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate in glycolysis?

Glycolysis would halt because NAD+ would not be reduced, preventing further oxidation of glucose. (B) Signup and view all the answers

How are the light-dependent and light-independent reactions of photosynthesis interconnected, and what would be the immediate impact of a sudden shortage of water on this relationship?

The light-dependent reactions produce ATP and NADPH, which are used in the light-independent reactions, and a water shortage would limit carbon dioxide uptake, indirectly affecting both stages. (A) Signup and view all the answers

How does feedback inhibition regulate metabolic pathways, and what are the potential consequences of a malfunction in this regulatory mechanism?

It inhibits early steps in a pathway by the final product and a malfunction could lead to overproduction of the end product. (D) Signup and view all the answers

Considering the chemiosmotic theory, what is the direct energy source that drives ATP synthesis by ATP synthase in both cellular respiration and photosynthesis?

The potential energy stored in a proton gradient across a membrane. (D) Signup and view all the answers

How do CAM plants minimize photorespiration compared to C3 plants, and under what environmental conditions is this adaptation most advantageous?

CAM plants fix carbon dioxide into a four-carbon compound at night and then release it to RuBisCO during the day, which is most advantageous in hot, dry conditions. (A) Signup and view all the answers

What is the theoretical maximum ATP yield from the complete oxidation of one glucose molecule during cellular respiration, and why do actual yields often fall short of this maximum?

38 ATP, but actual yields are lower due to the energy cost of transporting pyruvate and phosphate into the mitochondria and the proton leak across the mitochondrial membrane. (C) Signup and view all the answers

How does non-competitive inhibition affect the relationship between substrate concentration and enzyme activity, and why is it considered a more complex regulatory mechanism than competitive inhibition?

It decreases the $V_{max}$ without affecting the $K_m$, and it can involve binding at a site distinct from the active site, influencing enzyme conformation. (B) Signup and view all the answers

How does the electron transport chain contribute to the generation of a proton gradient, and what structural features of the inner mitochondrial membrane are essential for this process?

It uses the energy from electron transfer to actively transport protons across the inner mitochondrial membrane, which must be impermeable to protons except through ATP synthase. (D) Signup and view all the answers

What are the key regulatory points in glycolysis, and how do specific allosteric enzymes at these points respond to changes in cellular energy charge (ATP/AMP ratio)?

Phosphofructokinase is the main regulatory enzyme, inhibited by ATP and citrate, and activated by AMP, thus matching glycolysis rate to energy demand. (B) Signup and view all the answers

How do plants balance the need to open stomata for carbon dioxide uptake with the need to conserve water, especially under arid conditions?

By producing abscisic acid (ABA), which causes stomata to close, reducing water loss and limiting carbon dioxide uptake. (B) Signup and view all the answers

What role does the Krebs cycle play in both energy production and biosynthesis, and how are its intermediates replenished if they are drawn off for anabolic reactions?

It produces both ATP (indirectly) and key intermediates for biosynthesis; intermediates are replenished through anaplerotic reactions. (A) Signup and view all the answers

How does the oxygen-evolving complex (OEC) in photosystem II contribute to the process of photosynthesis, and what is the fate of the electrons extracted from water molecules?

It catalyzes the splitting of water molecules to release electrons, protons, and oxygen, with the electrons replacing those lost by chlorophyll in photosystem II. (C) Signup and view all the answers

What is the Warburg effect in cancer cells, and how does this metabolic adaptation contribute to their uncontrolled proliferation?

Cancer cells primarily use glycolysis, even in the presence of oxygen, resulting in increased production of biosynthetic precursors and supporting rapid proliferation. (A) Signup and view all the answers

Flashcards

Enzymes

Biological catalysts that speed up chemical reactions by lowering activation energy.

Respiration

A catabolic process that breaks down glucose to produce ATP, using oxygen.

Photosynthesis

An anabolic process where plants use light energy to convert CO2 and water into glucose and oxygen.

Metabolism

All of the chemical reactions that occur within a cell or organism.

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Study Notes

Course-related resources include syllabus outlines, command terms, reporting skills, and practical work guidance.
Key topics covered are Biomolecules, Cells, Metabolism, Genetics, Heredity, Equilibrium, Body Systems, Plant Systems, Biodiversity, Nutrition, Ecology, and Human Impacts.
Themes explored are Unity and Diversity, Form and Function, Interdependencies, and Continuity/Change.
Resources for review include PowerPoints, topic notes, summaries, and worksheets.
Enzymes, Respiration, and Photosynthesis are significant areas of study.

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