Metabolism and Energy

Metabolism

This is all chemical reactions and pathways that occur in a living organism to maintain life. It is a highly coordinated set of events to maintain energy homeostasis.

• Demand for and intake of energy not synchronized

• Constant adjustment of metabolic pathways

• Integration achieved by having a common currency (e.g., ATP) and few intermediates (e.g., acetyl-CoA and pyruvate) tying together the different pathways

Catabolic vs. anabolic reactions

One is breaking down macros, energy is released and transformed into ATP.

The other is synthesizing complex molecules from simple precursors by using the energy from ATP.

Regulatory enzymes

The direction of metabolic pathways are regulated by energy status of the cell, which determines which directions the reactions flow. Pyruvate and acetyl-CoA tie pathways together

Balancing catabolism and anabolism

Regulatory enzymes are located at strategic points in metabolic pathways and mostly unidirectional

Malonyl-CoA

This plays a role in both FA synthesis and β-oxidation. Allosterically controls carnitine acyltransferase. Concentration is highest in fed state, declines with fasting. Malonyl-CoA in skeletal muscle increased by glucose and insulin.

Role of AMP-activated protein kinase

This is a master energy sensor. AMPK controls both catabolic and anabolic pathways involving all the macronutrients.

• Activated by low energy (increases AMP:ATP ratio)

• Promotes glucose uptake in cells for glycolysis

• Promotes FA uptake into cardiac muscle for FA oxidation

What pathways occur in the liver?

Most nutrients pass through the liver first. The liver is the location for: glycolysis, glycogenesis, gluconeogenesis, deamination: use carbons for FA synthesis and gluconeogenesis, ureagenesis, AA synthesis, protein synthesis, β-oxidation of FA, de novo lipogenesis.

CHO metabolism in liver

FA metabolism in liver

AA metabolism in liver