Enzymes lower the activation energy, allowing reactions to proceed faster. They are not consumed (option A is false), activity is pH and temperature-dependent (option C is false), and not all enzymes need cofactors (option D is false).
Hexokinase catalyzes the first step of glycolysis, phosphorylating glucose to glucose-6-phosphate using ATP. Phosphofructokinase acts later in glycolysis, and aldolase is involved in splitting fructose-1,6-bisphosphate.
Isocitrate dehydrogenase is a rate-limiting enzyme in the citric acid cycle, regulated by ATP, ADP, and NADH levels. Citrate synthase and succinate dehydrogenase are important but less tightly regulated.
Oxygen acts as the final electron acceptor, forming water as a by-product. NAD⁺ and FAD are electron carriers, and water is a product, not the acceptor.
Competitive inhibitors compete with the substrate for binding at the enzyme's active site. They do not affect Vmax but increase the apparent Km. Increasing substrate concentration can overcome inhibition (option C is false), and they usually form reversible, non-covalent bonds.
