Final answer:
Phosphorylase a is more active when the cell requires energy, as signaled by hormones like adrenaline and glucagon, leading to its phosphorylation. It is part of the regulation of energy production in the cell, with various enzymes like phosphofructokinase playing roles in upregulating or downregulating metabolic pathways based on the cell's current energy status.
Step-by-step explanation:
The conditions when phosphorylase a is more active than phosphorylase b are typically related to the energy needs of a cell. Phosphorylase a and b are part of the glycogenolysis pathway, which is the breakdown of glycogen into glucose to be used for energy. Phosphorylase a is the phosphorylated, and thus more active, form of the enzyme. Its activity is upregulated in response to hormonal signals like adrenaline and glucagon, which indicate that the body needs more glucose for energy. The presence of these hormones triggers a cascade that results in the phosphorylation of phosphorylase b, converting it into phosphorylase a. Conversely, phosphorylase b, the less active form, is predominant when the cell is in a state of low energy demand.
In the context of glycolysis, enzymes like phosphofructokinase are regulated to ensure efficiency in energy production. Phosphofructokinase is inhibited by high levels of ATP and citrate, indicating that the cell has ample energy, and thus slowing down glycolysis is beneficial. This is a form of feedback inhibition, where the products of a pathway can regulate their own production through allosteric effects.