Biomedical Sciences – Comprehensive Metabolism Notes with In-Depth
Explanations
Amino Acids: Classification and Metabolic Origins
Amino acids (AAs) are fundamental to protein synthesis and numerous metabolic functions.
They are categorized as essential or non-essential based on the body's ability to synthesize
them.
Essential amino acids cannot be synthesized by humans and must be obtained through diet,
reflecting evolutionary adaptation to dietary availability.
Non-essential amino acids can be synthesized internally, often from intermediates of central
metabolic pathways. For example, serine is synthesized from 3-phosphoglycerate, an
intermediate in glycolysis, linking carbohydrate metabolism directly to amino acid
biosynthesis.
Furthermore, dihydroxyacetone phosphate (DHAP), another glycolytic intermediate, can be
converted into alpha-glycerol phosphate, which forms the backbone for triglycerides and
phospholipids, bridging carbohydrate and lipid metabolism.
Detailed Glycolysis: Steps 8 to 10 and Biochemical Significance
Step 8: The enzyme phosphoglycerate mutase catalyzes the reversible conversion of 3-
phosphoglycerate (3PG) to 2-phosphoglycerate (2PG). This is a mutase reaction, which
transfers a phosphate group within the molecule to reposition it, optimizing it for
subsequent energy-releasing steps. The reversibility allows the pathway to adapt to cellular
metabolic demands.
Step 9: Enolase dehydrates 2PG to form phosphoenolpyruvate (PEP), a compound with one
of the highest-energy phosphate bonds in metabolism. The removal of water is essential for
creating this high-energy intermediate, which is crucial for the subsequent substrate-level
phosphorylation.
Enolase is notably sensitive to fluoride ion inhibition. Fluoride binds to enolase, preventing
PEP formation and thus inhibiting the production of ATP in the final steps of glycolysis. This
mechanism explains fluoride's toxic effects on energy metabolism, especially in cells relying
heavily on glycolysis like red blood cells.
Step 10: Pyruvate kinase catalyzes the irreversible transfer of the phosphate group from
PEP to ADP, forming ATP and pyruvate. This reaction represents the second substrate-level
phosphorylation in glycolysis and is tightly regulated as a key control point for glycolytic
flux.
Explanations
Amino Acids: Classification and Metabolic Origins
Amino acids (AAs) are fundamental to protein synthesis and numerous metabolic functions.
They are categorized as essential or non-essential based on the body's ability to synthesize
them.
Essential amino acids cannot be synthesized by humans and must be obtained through diet,
reflecting evolutionary adaptation to dietary availability.
Non-essential amino acids can be synthesized internally, often from intermediates of central
metabolic pathways. For example, serine is synthesized from 3-phosphoglycerate, an
intermediate in glycolysis, linking carbohydrate metabolism directly to amino acid
biosynthesis.
Furthermore, dihydroxyacetone phosphate (DHAP), another glycolytic intermediate, can be
converted into alpha-glycerol phosphate, which forms the backbone for triglycerides and
phospholipids, bridging carbohydrate and lipid metabolism.
Detailed Glycolysis: Steps 8 to 10 and Biochemical Significance
Step 8: The enzyme phosphoglycerate mutase catalyzes the reversible conversion of 3-
phosphoglycerate (3PG) to 2-phosphoglycerate (2PG). This is a mutase reaction, which
transfers a phosphate group within the molecule to reposition it, optimizing it for
subsequent energy-releasing steps. The reversibility allows the pathway to adapt to cellular
metabolic demands.
Step 9: Enolase dehydrates 2PG to form phosphoenolpyruvate (PEP), a compound with one
of the highest-energy phosphate bonds in metabolism. The removal of water is essential for
creating this high-energy intermediate, which is crucial for the subsequent substrate-level
phosphorylation.
Enolase is notably sensitive to fluoride ion inhibition. Fluoride binds to enolase, preventing
PEP formation and thus inhibiting the production of ATP in the final steps of glycolysis. This
mechanism explains fluoride's toxic effects on energy metabolism, especially in cells relying
heavily on glycolysis like red blood cells.
Step 10: Pyruvate kinase catalyzes the irreversible transfer of the phosphate group from
PEP to ADP, forming ATP and pyruvate. This reaction represents the second substrate-level
phosphorylation in glycolysis and is tightly regulated as a key control point for glycolytic
flux.
