Understanding Metabolism: Catabolic and Anabolic Pathways

Posted on Mar 22, 2025 in Biochemistry

Metabolism:

Catabolic Reactions:

  • Degradation of macromolecules to monomers, metabolic intermediates, and simple final products
  • Oxidation
  • Gain energy (ATP, NADH)

Anabolic Reactions:

  • Synthesis of complex molecules from simple molecules
  • Reduction
  • Energy expenditure

This route has three levels of complexity:

  1. Interconversion of polymers and lipid complexes
  2. Interconversion of sugars, amino acids, and lipids
  3. Degradation ends up as inorganic compounds

Nucleotide Catabolism in Nicotinamide Biosynthesis:

NAD+ acts as a cofactor in the direction of oxidation of the substrates, and NADPH reductases.

NADPH is synthesized from NADP+.

NADP+ is synthesized from NAD+ by the action of ATP-dependent kinase.

Mechanisms of ATP Synthesis

Oxidative Phosphorylation:

Performed in the electron transport chain in mitochondria. NADH and FADH2 produced in glycolysis and the citric acid cycle are oxidized to provide energy for ATP synthesis.

Substrate-Level Phosphorylation:

Phosphate groups with high-energy bonds are transferred directly from one substrate to ADP. ATP is synthesized by this mechanism in glycolysis and the citric acid cycle.

Glycogenolysis:

Glycogen degradation in response to low blood glucose.

Glycogenesis:

Formation of glycogen when the available glucose exceeds the needs of ATP.

Glycolysis:

  • Glucose is oxidized to pyruvate
  • NAD+ is reduced to NADH
  • ATP is synthesized by substrate-level phosphorylation
  • Series of 10 consecutive reactions
  • It occurs in the cytoplasm and does not require the presence of O2

Glucose + 2 NAD+ + 2ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2H+ 2 ATP + 2H2O

The continued use of glucose in glycolysis leads to accumulation of NADH and NAD+ depletion.

This must be replenished by reoxidation of NADH in:

  • Electron transport chain

Fermentation:

Lactic Fermentation: An anaerobic cellular process which uses glucose for energy, and the waste product is lactic acid. The acellular generates molecules that NAD+ has been consumed him proiceso of glycolysis, the cell is transformed and becomes oxidized, the ac. Obtained from 2 ATP, but in this process using 2 NAD+ as electron acceptor and reduced to NADH, giving 2 H+ to ac. Pyruvic which is reduced to lactic acid.

Ethanol Fermentation: Process in the absence of O2. Exothermic reactions release CO2 reduction reaction 2NAD+ to NADH, with a bottom line that turn 2 ADP into ATP. Decarboxylated by the action of pyruvate decarboxylase pyruvate to give a final product acetaldehyde, thus liberated apartir CO2 H+ and NADH. The synthesized NADH reoxidized by OH dehydrogenase, NAD+ and synthesizing Regera while ethanol.

Conversion of Pyruvate to Acetyl-CoA by Pyruvate Dehydrogenase (Multienzyme Complex)

  • Decarboxylation
  • Oxidation: Production of NADH
  • Formation of acetyl-CoA: acetyl group binds to the coenzyme A, through-S to form acetyl-CoA

If oxygen is present, pyruvate is decarboxylated in the mitochondria, producing acetyl-CoA, NADH, and pyruvate CO2 + NAD+ acetyl-CoA + NADH + CO2