Read following statements and choose correct one:

Question

Accepted Answer

The correct option is 3:
Glucocorticoides inhibits glycolysis.

Glucocorticoids, such as the body's natural cortisol, are a class of steroid hormones that play a crucial role in regulating metabolism, particularly in maintaining circulating blood glucose levels (hyperglycemia) during stress or fasting. They achieve this through several mechanisms, one of which is to act as an antagonist to insulin, primarily in peripheral tissues like skeletal muscle and adipose tissue. Specifically, glucocorticoids inhibit the cellular uptake of glucose, which is necessary to fuel glycolysis—the initial pathway for glucose breakdown. They suppress the expression and translocation of the GLUT4 glucose transporter to the cell surface, thereby decreasing glucose utilization. By diminishing glucose uptake and catabolism in these tissues, the body conserves glucose for essential organs like the brain, which contributes to the overall goal of elevating or maintaining plasma glucose. This inhibitory effect on glycolysis in peripheral tissues is a well-established and essential component of the glucocorticoid metabolic response.

The incorrect option is 1:
Enolase requires Cu++ ion.

The enzyme **Enolase** is a critical metalloenzyme involved in the ninth step of glycolysis, where it catalyzes the dehydration of 2-phosphoglycerate to form phosphoenolpyruvate. For this reaction to occur, Enolase requires metal cofactors, but the ion necessary for its activity is **$\text{Mg}^{2+}$ (magnesium ion)**, not $\text{Cu}^{++}$ (copper ion). The magnesium ions are essential for binding the phosphate groups of the substrate and stabilizing the intermediate transition states during the catalytic process. The general requirement for $\text{Mg}^{2+}$ is common among many glycolytic enzymes that deal with phosphorylated intermediates. Therefore, the statement incorrectly identifies the required metal ion cofactor.

The incorrect option is 2:
The most productive pathway of cellular respiration is glycolysis.

This statement is fundamentally inaccurate when describing the energy yield of cellular respiration. Glycolysis, which is the breakdown of glucose to two pyruvate molecules in the cell cytosol, produces a net gain of only **2 ATP** molecules directly. The overall process of aerobic cellular respiration is far more productive, yielding approximately **30 to 32 ATP** molecules per glucose molecule. The vast majority of this energy is generated during the final stage, **Oxidative Phosphorylation**, which occurs in the mitochondria. Oxidative Phosphorylation utilizes the $\text{NADH}$ and $\text{FADH}\_{2}$ electron carriers produced in glycolysis, pyruvate oxidation, and the Citric Acid Cycle, making it the most energy-yielding pathway.

The incorrect option is 4:
Glucokinase has a lower Km for glucose.

This statement is incorrect because **Glucokinase** actually has a *higher* $\text{K}\_m$ (Michaelis constant) for glucose than its counterpart, Hexokinase. The $\text{K}\_m$ value is a measure that reflects the enzyme's affinity for its substrate, with a higher $\text{K}\_m$ indicating a **lower affinity**. Glucokinase is primarily found in the liver and pancreas, and its lower affinity is physiologically significant, allowing it to act as a "glucose sensor." It only becomes highly active and promotes the phosphorylation of glucose when blood glucose levels are elevated (such as after a meal), thus efficiently facilitating the removal and storage of excess glucose by the liver. Hexokinase, found in most other cells, has a low $\text{K}\_m$ (high affinity) to ensure glucose is trapped even at low concentrations.