Test: Principles of Bioenergetics - 2 - MCAT MCQ

A negative ΔG value indicates that the reaction is exergonic, meaning it releases energy. In this case, the ΔG value of -686 kcal/mol suggests that the reaction is exergonic, releasing 686 kilocalories of energy per mole of reaction.

The addition of a catalyst does not change the overall free energy change (ΔG) of a reaction. A catalyst speeds up the rate of the reaction by lowering the activation energy required for the reaction to occur. However, it does not affect the thermodynamics or the overall energy change associated with the reaction. Therefore, the addition of a catalyst would not reduce the ΔG value of -686 kcal/mol.

The ATP/ADP cycle couples endergonic and exergonic reactions in human physiology. ATP (adenosine triphosphate) is a molecule that stores and releases energy in cells. When ATP is hydrolyzed (broken down) into ADP (adenosine diphosphate) and inorganic phosphate (Pi), it releases energy. This hydrolysis of ATP is an exergonic reaction because it results in the release of energy.

The released energy from ATP hydrolysis can be used to drive endergonic reactions, which require an input of energy to occur. In these reactions, ADP and Pi can be coupled together through a process called phosphorylation, resulting in the formation of ATP. This phosphorylation reaction is an endergonic reaction because it requires an input of energy.

Overall, the ATP/ADP cycle couples endergonic reactions (phosphorylation of ADP) with the exergonic reaction (hydrolysis of ATP). Energy released from the exergonic reaction of ATP hydrolysis is utilized to drive the endergonic reaction of ATP synthesis, allowing cells to continuously regenerate ATP and maintain their energy supply.

According to Le Chatelier's principle, an increase in the concentration of one of the reactants or products in a reversible reaction will shift the equilibrium in the direction that consumes or reduces the concentration of that substance. In the case of the ATP/ADP cycle, an increase in ADP levels would favor the conversion of ADP to ATP.

The reaction ADP + Pi ⇌ ATP involves the addition of inorganic phosphate (Pi) to ADP to form ATP. If ADP levels increase, the equilibrium will shift towards the formation of ATP, consuming the excess ADP and inorganic phosphate to produce more ATP molecules. As a result, the levels of inorganic phosphate would decrease.

If an antibiotic fails to distort the binding site of bacterial enzymes, it means that the antibiotic is unable to effectively interact with and inhibit the enzymes. This can lead to increased bacterial resistance to the antibiotic. Bacteria may have mechanisms, such as mutations or changes in enzyme structure, that prevent the antibiotic from binding to the target enzyme and interfering with its activity. As a result, the bacteria are able to continue their enzymatic activities and survive the antibiotic treatment, leading to increased resistance.

In competitive enzymatic inhibition, the symptoms of a disease are a result of an inhibitor molecule competing with the substrate for the active site of the enzyme. By increasing the levels of substrate, the aim is to overcome the inhibitory effect of the inhibitor and restore enzyme activity. With higher substrate concentrations, there will be a greater chance for substrate molecules to bind to the active site of the enzyme and outcompete the inhibitor. This can help minimize the symptoms associated with the disease by promoting the enzymatic reactions and restoring normal cellular functions.

In anaerobic conditions where oxygen is not present, the electron transport chain cannot proceed as usual. Without oxygen as the final electron acceptor, the electron transport chain is disrupted, leading to a buildup of electron carriers (such as NADH) and a limitation in the regeneration of electron carrier molecules.

Under anaerobic conditions, alternative pathways, such as fermentation, may be utilized to regenerate NAD+ from NADH, allowing for continued glycolysis and ATP production. However, these anaerobic pathways are generally less efficient in terms of ATP production compared to aerobic respiration.

To specifically address the question, in the absence of oxygen, the anaerobic reaction in the electron transport chain would be less exergonic compared to the reaction in the presence of oxygen.

During muscle contraction, ATP is hydrolyzed to ADP and inorganic phosphate (Pi) to provide the energy needed for the contraction process. ATP hydrolysis is an exergonic reaction, meaning it releases energy. This energy is utilized by the muscles to generate force and perform work.

Some of the energy released from ATP hydrolysis is used for muscle contraction, but not all of it is converted into mechanical work. A significant portion of the energy is dissipated as heat. This increase in heat production during muscle contraction contributes to the rise in body temperature.

In the process of oxygen binding and release in hemoglobin (Hb) molecules, oxygen acts as an allosteric activator. Allosteric regulation refers to the binding of a molecule to a site on the protein that affects the protein's activity at a different site.

When oxygen binds to one of the oxygen binding sites in Hb, it induces a conformational change in the protein structure, making it easier for subsequent oxygen molecules to bind to the remaining sites. This positive-feedback mechanism enhances the affinity of Hb for oxygen and promotes the loading of oxygen onto Hb in the lungs or oxygen-rich environment.

Conversely, in oxygen-deprived tissues, the binding of oxygen to Hb is weakened, leading to the release of oxygen from the remaining binding sites. This facilitates the unloading of oxygen to the tissues that are in need of oxygen for metabolic processes.

During aerobic respiration, glucose is oxidized through glycolysis, the citric acid cycle (Krebs cycle), and the electron transport chain. These processes generate energy in the form of ATP and reduced electron carriers (NADH and FADH2). The complete oxidation of one molecule of glucose results in the production of approximately 36-38 ATP molecules through oxidative phosphorylation in the electron transport chain. Additionally, 2 FADH2 molecules are generated in the citric acid cycle.

During photosynthesis, light-dependent reactions occur in the thylakoid membranes of chloroplasts and involve the absorption of light energy by chlorophyll. In these reactions, water is split, generating oxygen, ATP, and NADPH. The ATP and NADPH produced in the light-dependent reactions are then used as energy and reducing power in the light-independent reactions (Calvin cycle), which occur in the stroma of chloroplasts. In the light-independent reactions, carbon dioxide is fixed and converted into glucose using the energy and reducing power provided by ATP and NADPH from the light-dependent reactions.