Following a meal, the pancreas releases insulin to manage elevated blood sugar levels by altering how various tissues process nutrients. This hormone primarily targets the liver, muscles, and fat cells to encourage the storage of energy while preventing the release of internal fuel reserves. Specifically, insulin facilitates the movement of glucose from the bloodstream into cells via specialized transporters and promotes the synthesis of glycogen and fats. Simultaneously, it halts processes like gluconeogenesis and lipolysis, ensuring that the body stops producing sugar and breaking down fat when food is available. By coordinating these stimulatory and inhibitory actions, insulin effectively maintains metabolic balance and nutrient distribution. The overall process shifts the body into an anabolic state, focusing on cellular uptake and long-term energy conservation.

Metabolism involves a structured three-stage breakdown of nutrients to provide the body with energy. The initial phase takes place in the digestive tract, where complex foods like proteins and fats are reduced to their basic building blocks before entering the blood. During the second stage, these smaller units travel into cells to be processed within the cytoplasm and mitochondria, creating high-energy molecules through pathways like glycolysis and the TCA cycle. The final phase occurs deep inside the mitochondrial membrane, focusing on converting those molecules into ATP. This essential end product serves as the primary fuel source for all cellular activities. By following this sequence, the body efficiently transforms dietary intake into usable biological power.

Triacylglycerol, the major (90%) dietary fat is processed specifically by 3 distinct lipases with 3 distinct compartments, resulting in digestion, absorption, reassembly, transport and uptake by tissues. During fasting, lipoprotein lipase mobilizes stored triacylglycerol in adipose tissue, releasing fatty acids to the bloodstream and providing an alternative energy source for several tissues.

The body cannot store excess amino acids, so they are used for protein synthesis or energy. During catabolism, nitrogen is converted into toxic ammonia, which the urea cycle safely removes. Remaining carbon skeletons are repurposed for fuel by producing glucose or acetyl CoA which are both catabolized to produce energy.

This podcast summarizes 5 key features of glycolysis: 1. Purpose of glycolysis ; 2. Tissues and Cellular compartments; 3. Energy output; 4. Regulation of rate-limiting enzymes; and 5. Clinical correlates (pyruvate kinase are deficiency).

This podcast explains how the human body adapts its metabolic pathways to manage pyruvate based on its nutritional status. In the well-fed state, high glucose levels allow pyruvate to fuel the TCA cycle for energy or assist in creating nonessential amino acids. Conversely, during fasting or physical exertion, the body shifts toward gluconeogenesis to synthesize new glucose from available resources. This process involves converting substances like lactate and alanine from the muscles back into pyruvate within the liver. Ultimately, the source highlights the body’s metabolic flexibility in maintaining energy balance through varying physiological conditions.

Insulin binding to its receptor initiates a cascade of intracellular events that lead to the activation of a phosphoprotein phosphatase. This phosphatase will dephosphorylate 8 distinct enzymes involved in carbohydrate and lipid metabolism and change their activity, thus changing the overall metabolism of carbohydrates and lipids.

In this short, the effect of allosteric effectors on enzyme kinetics is covered in some detail including the effect of allosteric effectors on either Vmax or the the enzyme's affinity for its substrate.