Glycolysis: Glucose is converted to pyruvate through a series of enzyme-catalyzed reactions.
Krebs Cycle (Citric Acid Cycle): Pyruvate is converted to acetyl-CoA, which reacts with oxaloacetate to form citrate, entering a cycle of reactions to regenerate oxaloacetate.
Both glycolysis and the Krebs cycle are referred to as central metabolism as they are crucial for ATP production.
ATP Production
Central metabolism produces ATP, the cell's energy source.
Cofactors: NADH and FADH2 are produced, donating electrons to the electron transport chain to generate more ATP.
Variety of Metabolic Inputs
Monosaccharides: Other sugars like galactose can enter metabolism as intermediates.
Proteins and Amino Acids: Amino acids can enter metabolism after deamination (removal of nitrogen), forming alpha-keto acids.
Fatty Acids: Undergo beta-oxidation, forming NADH, FADH2, and acetyl-CoA.
Biosynthesis and Catabolism
Gluconeogenesis: Pyruvate can be converted back to glucose.
Amino Acids: Some amino acids can be converted into glucose precursors.
Fatty Acids: Generally cannot be converted into glucose but provide acetyl-CoA for other syntheses.
Energy Storage and Use
Fed State: Excess glucose and amino acids convert to triglycerides for storage.
Fasted State: Triglycerides are broken down to provide energy.
Specialized Metabolic Pathways
Ketogenesis: Acetyl-CoA in the liver forms ketone bodies as an energy source during fasting.
Cholesterol Synthesis: Acetyl-CoA can also contribute to cholesterol and steroid hormone synthesis.
Biosynthesis of Important Molecules
Amino Acids and Proteins: Central intermediates support the synthesis of non-essential amino acids.
Neurotransmitters: Dopamine, serotonin, and others are synthesized from metabolic intermediates.
Hemoglobin and Myoglobin: Formed from a porphyrin ring built from central metabolism intermediates.
Limitations of Central Metabolism
Vitamins and minerals cannot be synthesized through central metabolism and must be obtained from the diet.
Antioxidant Systems
Glutathione System: Reduces oxidative damage by neutralizing free radicals.
Complex Interconnections
Multiple pathways interconnect to sustain cell viability and function, proving central metabolism's importance.