Question

How are metabolic processes regulated so that the energy and biosynthetic requirements of organisms are consistently met?

Answer 1

Metabolic processes are a balance of biosynthetic and catabolic processes.

These processes are regulated by regulatory enzymes, co-factor molecules as well as hormones.

The balance between anabolism and catabolism is maintained via insulin and glucagon in the pancreas.

Glucagon is secreted by alpha cells while insulin is secreted by beta cells in response to the amount of glucose in the blood. When the blood glucose level increases, glucose binds to the GLUT2 receptor protein present in the beta cells in order to stimulate the production of insulin. Insulin promotes anabolism by stimulating skeletal muscle cells and adipocytes to incorporate GLUT4 into the plasma membranes. This in turn increases cellular uptake and glucose utilization via cellular respiration to release ATP which is the currency of energy in cells.. Glucose is converted to ATP via glycolysis, Krebs cycle, and electron transport chain. 1 Glucose molecule produces 38 ATP molecules, 2 from glycolysis, 2 from the Krebs cycle, and 34 from the electron transport system.

Alternatively, when the blood glucose level decreases, alpha cells secrete glucagon to facilitate glycogenolysis and gluconeogenesis in order to produce more glucose from the reserves stored in muscles and liver by promoting lipolysis and ketogenesis. Other hormones that signal low blood glucose are cortisol and epinephrine. These signal molecules bind to receptors in the plasma membrane that in turn activate signal cascades via co-factors such as cAMP and messengers that promote lipolysis and gluconeogenesis.