MODULE 8: Chapter 9.1 Flashcards
What are catabolic pathways?
The collection of enzymatic reactions in the cell that lead to the degradation of macromolecules and nutrients for energy capture, usually in the form of ATP and reducing power (NADH and FADH2).
What are anabolic pathways?
Pathways that use energy from ATP hydrolysis and the oxidation of reducing equivalents (primarily NADPH) to synthesize biomolecules for the cell.
What two primary factors determine the flux of metabolites through pathways?
- Level of enzyme activity * Level of substrates
How does enzyme activity affect metabolic pathways?
Enzyme activity is controlled by enzyme levels, catalytic activity, and cellular location.
What is the role of enzymes in metabolic reactions?
Enzymes provide a suitable reaction environment that lowers the energy of activation for a given reaction and function as catalysts that increase reaction rates.
What happens to blood glucose levels before breakfast?
Blood glucose levels begin to decline after a night of fasting, triggering glucagon release from the pancreas.
What effect does glucagon signaling have in liver cells?
It activates glycogen degradation (catabolic pathway) and gluconeogenesis (anabolic pathway) while inhibiting glycolysis.
What occurs after breakfast in terms of insulin levels?
Insulin levels increase due to elevated blood glucose, stimulating glucose uptake, glycogen synthesis, and glycolytic pathway activity.
What is the significance of metabolic pathways in relation to nutrition, exercise, and disease?
Metabolic pathways are highly interdependent and controlled by enzyme activity levels and substrate concentration.
What are the four classes of macromolecules in metabolism?
- Proteins * Nucleic acids * Carbohydrates * Lipids
What are the six primary metabolites encountered in metabolism?
- Amino acids * Nucleotides * Fatty acids * Glucose * Pyruvate * Acetyl-CoA
What are the seven small biomolecules frequently encountered in metabolism?
- NH4+ * CO2 * NADH * FADH2 * O2 * ATP * H2O
What are the ten major metabolic pathways in plants and animals?
- Glycolysis * Citrate cycle * Oxidative phosphorylation * Photosynthesis and carbon fixation * Pentose phosphate pathway * Gluconeogenesis * Glycogen degradation and synthesis * Fatty acid degradation and synthesis * Nitrogen fixation and assimilation * Urea cycle
What is the definition of flux in a metabolic pathway?
The rate at which substrates and products (metabolites) are interconverted.
How is the overall change in free energy (ΔG) calculated for a defined metabolic pathway?
ΔG = ΔG°′ + RT ln Q
What does a large negative ΔG°′ indicate?
That the reaction proceeds favorably from left to right.
What does a large positive ΔG°′ indicate?
That the reaction proceeds from right to left.
What is the significance of coupled reactions in metabolism?
They allow unfavorable reactions to occur by coupling them with favorable ones.
What is the ΔG°′ value for ATP hydrolysis?
−30.5 kJ/mol
What is the mass action ratio (Q) in metabolic pathways?
The ratio of the product and substrate concentrations under actual conditions in the cell.
What is the overall ΔG for a metabolic pathway indicative of?
The driving force to reach equilibrium under cellular conditions.
What drives ATP synthesis in metabolism?
Pyruvate formation is high enough to drive ATP synthesis.
How is metabolic flux calculated?
By calculating the overall change in free energy (ΔG) using the mass action ratio (Q).
What is the mass action ratio (Q)?
The ratio of the product and substrate concentrations under actual conditions in the cell.
What does the overall ΔG for a metabolic pathway indicate?
The driving force to reach equilibrium under cellular conditions.
Are metabolic reactions at equilibrium in a living organism?
No, they are not at equilibrium; equilibrium occurs only when the organism dies.
What is the biochemical standard free energy change (ΔG°′) for the phosphoglucoisomerase reaction?
+1.7 kJ/mol
What is the ΔG for the phosphoglucoisomerase reaction when fructose-6-P concentration is low?
-2.9 kJ/mol
How can an unfavorable reaction be driven forward?
By coupling it with a favorable reaction.
What is a shared intermediate in coupled reactions?
Fructose-6-P in the glycolytic pathway.
What role do multiprotein complexes play in metabolism?
They increase the efficiency of coupled reactions through substrate channeling.
What types of complexes promote substrate channeling between metabolic enzymes?
- Cytosolic protein complexes
- Membrane-bound protein complexes
- Protein complexes formed by binding to a shared scaffold protein
What evidence supports the concept of metabolite channeling?
- High-affinity noncovalent interactions between glycolytic enzymes
- Kinetic data showing faster reaction rates in protein aggregates compared to dilute solutions
What is the equation for the actual change in free energy (ΔG) for a reaction?
ΔG = ΔG°′ + RT ln Q
What happens to ΔG when a large amount of substrate enters the cell?
It results in a more negative ΔG.
What is KEGG?
A set of databases that map the integrated systems of molecular interactions within a cell or organism.
What is the definition of the mass action ratio (Q)?
The ratio of the concentration of product over the concentration of substrate, under actual conditions in a cell.
Is the reaction catalyzed by enolase in glycolysis more or less favorable under actual conditions if ΔG°′ = +1.7 kJ/mol and 2-phosphoglycerate concentration is 10 times higher than phosphoenolpyruvate?
More favorable under actual conditions.
