Final answer:
Covalent modifications are used in glycogen metabolism to regulate enzymes such as glycogen phosphorylase and glycogen synthase through reversible phosphorylation, controlling the storage and release of glucose as needed for energy.
Step-by-step explanation:
Covalent modifications play a key role in glycogen metabolism, which involves the processes of glycogenolysis (breakdown of glycogen) and glycogenesis (synthesis of glycogen). In glycogen metabolism, enzymes are regulated by reversible covalent modification, which includes phosphorylation or dephosphorylation, leading to either activation or inhibition of the enzyme's activity. For example, glycogen phosphorylase is the key enzyme in glycogenolysis, and its activity is regulated by phosphorylation. During glycogenolysis, this enzyme cleaves glucose units from the non-reducing ends of glycogen through a phosphorolysis reaction, producing glucose 1-phosphate
. Glycogen synthesis or glycogenesis involves a different set of enzymes, such as glycogen synthase, which is also regulated through covalent modification. Activation of glycogen synthase promotes the conversion of activated glucose (UDP-glucose) into glycogen. In response to hormonal signals, such as insulin or glucagon, these enzymes may undergo covalent modifications altering their activities, thus balancing glycogen storage and release according to the body's energy needs.