Cell Metabolism and Fermentation Quiz

Lactic Acid Fermentation

• Involves the conversion of carbohydrates into lactic acid, primarily by certain bacteria and fungi.
• Plays a critical role in energy production under anaerobic conditions.

Cori Cycle

• A metabolic pathway that recycles lactate produced during anaerobic glycolysis back to glucose in the liver.

Pentose Phosphate Pathway (PPP)

• Functions as an alternative to glycolysis, generating NADPH and ribose-5-phosphate for nucleotide synthesis.
• Two main phases:
  • Oxidative phase produces NADPH and a pentose sugar.
  • Non-oxidative phase regenerates glucose-6-phosphate from ribose-5-phosphate.
• Significant connection to NADPH in combating oxidative stress.
• Clinical relevance highlighted by glucose-6-phosphate dehydrogenase (G6PD) deficiency.

Glycolysis Review

• Central metabolic pathway for glucose oxidation across all tissues, yielding approximately -2840 kJ/mol of energy.
• Glucose is essential for energy production and serves as a precursor for various metabolic pathways.
• Results in the production of pyruvate as the end product.
• Key outputs include:
  • 4 ATP, needed for energy-requiring cellular processes.
  • 2 NADH, which must be reoxidized to continue glycolysis.

Regulation of Glycolysis

• Heavily regulated to ensure effective nutrient use and ATP production.
• Hexokinase is characterized by higher affinity for glucose; high Km values indicate low affinity.

Gluconeogenesis

• Synthesizes glucose from non-carbohydrate precursors to supply glucose-dependent cells (e.g., RBCs).
• Vital during prolonged fasting, particularly for brain function which relies predominantly on glucose.
• Energetically expensive, operating primarily in the liver.

Pyruvate Fates

• Under anaerobic conditions, pyruvate can convert to either lactate or ethanol (not in humans).
• Transformation of pyruvate is contingent on environmental oxygen levels.

Gluconeogenesis Precursors

• Uses lactate, pyruvate, and oxaloacetate as substrates.
• Glucogenic amino acids contribute by entering the citric acid cycle.
• Fatty acids cannot be converted into glucose due to their metabolism producing acetyl-CoA, which cannot yield oxaloacetate.

Differences Between Glycolysis and Gluconeogenesis

• Their pathways are thermodynamically favorable, but they operate in reverse directions.
• Involves several key enzymes that facilitate irreversible steps of glycolysis to form glucose.

Enzymes in Gluconeogenesis

• Notable enzymes include:
  • Pyruvate carboxylase converts pyruvate to oxaloacetate.
  • Phosphoenolpyruvate carboxykinase (PEPCK) further converts oxaloacetate to phosphoenolpyruvate.
  • Fructose-1,6-bisphosphatase regulates the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate.

Reciprocal Regulation

• Generally regulated by fluctuations in metabolites; increases in reactants stimulate product formation, while increases in products can inhibit further synthesis.
• Key regulatory elements include citrate (activating gluconeogenesis) and AMP (inhibiting it), reflecting energy status in the cell.

Additional Gluconeogenesis Sources

• Glycerol, released from adipose tissue, can be converted to glucose; the process includes enzymes like glycerokinase and glycerol-3-phosphate dehydrogenase.
• Propionate from odd-chain fatty acids and certain amino acids can also enter gluconeogenesis through conversion to succinyl-CoA before producing glucose.

Test your knowledge on lactic acid fermentation, the Cori Cycle, and the Pentose Phosphate Pathway. This quiz covers the major metabolic pathways of glucose and their importance in organisms. Dive into the details of oxidative and nonoxidative phases, including their roles in generating NADPH.