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Biochemical Pathways: A Comparative Analysis of Energy Transfer in Photosynthesis and Cellular Respiration

An essay comparing the biochemical processes of photosynthesis and cellular respiration in energy transfer.

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    Biochemical Pathways: A Comparative Analysis of Energy Transfer in Photosynthesis and Cellular Respiration Essay Questions: 1. Define ΔG and describe how it relates to changes in entropy and enthalpy. H ow ΔG is related to the equilibrium constant of a reversible reaction and explain why cells maintain product/substrate concentrations below the equilibrium constant in metabolic pathways? Answer: ΔG (Gibbs free energy) represents the energy available to do work in a system at constant temperature and pressure. It relates to changes in entropy (ΔS) and enthalpy (ΔH) by the equation: • ΔH is the change in enthalpy (heat content), • T is the temperature in Kelvin, • ΔS is the change in entropy (disorder). If ΔG is negative, the reaction is spontaneous. If ΔG is positive, the reaction is non - spontaneous. Equilibrium and ΔG : At equilibrium, ΔG = 0. The relationship between ΔG and the equilibrium constant (K) is given by: where R is the gas constant and T is the temperature. A large K (favorable reaction) means a negative ΔG, and a small K means a positive ΔG. Cells maintain product/substrate concentrations below equilibrium to ensure reactions proceed in the direction that supplies energy (negative ΔG), preventing equilibrium from being reached and sustaining metabolic processes.

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    2. Why ATP is considered as an energy currency of the cells? B y giving examples describe how ATP provides energy for driving endergonic reactions. G iving an example show how ATP is produced by substrate level phosphorylation in glycolysis. Answer: ATP is considered the energy currency of the cell because it stores and transfers energy for biochemical reactions. It is a high - energy molecule due to the phosphate bonds, which, when broken (hydrolyzed), release energy that can be used by the cell. ATP and Endergonic Reactions: Endergonic reactions require an input of energy. ATP provides this energy through coupling . When ATP is hydrolyzed (ATP → ADP + Pi), it releases energy that is used to drive the endergonic reaction. For example: • Muscle contraction : ATP provides energy to myosin for muscle movement. • Active transport : ATP powers pumps like the sodium - potassium pump to move ions against their concentration gradient. ATP Production by Substrate - Level Phosphorylation: In glycolysis , ATP is produced by substrate - level phosphorylation, where a phosphate group is directly transferred from a substrate to ADP to form ATP. Example : During glycolysis, 1,3 - bisphosphoglycerate transfers a phosphate group to ADP, forming ATP and 3 - phosphoglycerate . The reaction: This process occurs twice in glycolysis, producing 2 ATP molecules per glucose molecule.

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    3. Briefly describe various ways enzymes are regulated by inhibitors. Answer: Enzymes are regulated by inhibitors in several ways, which can either decrease or stop enzyme activity. These include: 1. Competitive Inhibition: • Mechanism : An inhibitor resembles the substrate and competes for the enzyme’s active site. • Effect : The inhibitor blocks the substrate from binding, reducing the reaction rate. • Example : Methotrexate inhibits the enzyme dihydrofolate reductase by competing with folate. 2. Non - Competitive Inhibition: • Mechanism : The inhibitor binds to a site other than the active site (allosteric site), causing a conformational change in the enzyme that reduces its activity. • Effect : The enzyme’s function is altered, even if the substrate can still bind to the active site. • Example : Cyanide inhibits cytochrome c oxidase by binding to an allosteric site. 3. Uncompetitive Inhibition: • Mechanism : The inhibitor binds only to the enzyme - substrate complex, preventing the reaction from proceeding. • Effect : Reduces both enzyme activity and the amount of product formed. • Example : Lithium inhibits certain enzymes in neurotransmitter metabolism through uncompetitive inhibition. 4. Allosteric Inhibition: • Mechanism : Inhibitors bind to an allosteric site (distinct from the active site),

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