Biochemistry: Anabolic vs. Catabolic Pathways

Anabolic vs. Catabolic Pathways

• Anabolic pathways: Build complex molecules from simpler ones; require energy input (endergonic).
• Catabolic pathways: Break down complex molecules into simpler ones; release energy (exergonic).
• Energy Flow: Anabolic pathways require energy input while catabolic pathways release energy.

Free Energy and Spontaneity

• Free energy (G): The amount of available energy to do work.
• Change in free energy (ΔG): Determines a reactions spontaneity.
  • ΔG < 0: Spontaneous (exergonic)
  • ΔG > 0: Non-spontaneous (endergonic)
• Entropy (S): A measure of disorder, spontaneous reactions increase entropy.

Enzyme Function

• Activation energy (EA): Energy required to start a reaction.
• Enzymes lower the EA: This speeds up reactions without changing the overall free energy change (ΔG).
• Active site: Binds to substrates, stabilizing the transition state.
• Catalysis: Enzymes can orient substrates, stress bonds, or provide a microenvironment to accelerate reactions.

Secondary Molecules in Enzyme Function

• Cofactors: Non-protein molecules that help enzymes function (e.g., metal ions).
• Coenzymes: Organic molecules that aid in enzyme activity (e.g., vitamins).
• Inhibitors: Reduce enzyme activity
  • Competitive inhibitors: Bind to the active site.
  • Non-competitive inhibitors: Bind elsewhere on the enzyme.

Redox Reactions

• Oxidation: The loss of electrons from a molecule (e.g., glucose → CO₂).
• Reduction: The gain of electrons by a molecule (e.g., oxygen → H₂O).
• Coupled reactions: Oxidation and reduction always occur together.

The Four Stages of Cellular Respiration

• Glycolysis:
  • Location: Cytoplasm
  • Inputs: Glucose, 2 NAD⁺, 2 ATP
  • Outputs: 2 Pyruvate, 2 NADH, 4 ATP (net 2 ATP)
  • Key point: Breaks down glucose into pyruvate and produces a small amount of ATP.
• Oxidation of Pyruvate:
  • Location: Mitochondrial matrix
  • Inputs: 2 Pyruvate, 2 NAD⁺, 2 Coenzyme A
  • Outputs: 2 Acetyl-CoA, 2 NADH, 2 CO₂
  • Key point: Converts pyruvate into Acetyl-CoA for the citric acid cycle.
• Citric Acid Cycle (Krebs Cycle):
  • Location: Mitochondrial matrix
  • Inputs: 2 Acetyl-CoA, 6 NAD⁺, 2 FAD
  • Outputs: 6 NADH, 2 FADH₂, 2 ATP, 4 CO₂
  • Key point: Generates electron carriers (NADH and FADH₂) and ATP while releasing CO₂.
• Oxidative Phosphorylation:
  • Location: Inner mitochondrial membrane
  • Components: Electron Transport Chain (ETC) and Chemiosmosis
  • Inputs: NADH, FADH₂, O₂, ADP + Pi
  • Outputs: 34 ATP, H₂O
  • Key points:
    • Electron Transport Chain (ETC): Electrons from NADH and FADH₂ are passed down the chain to oxygen, creating a proton gradient.
    • Chemiosmosis: Protons flow through ATP synthase to generate ATP.

Fermentation (Anaerobic Respiration)

• Purpose: In the absence of oxygen, cells use fermentation to regenerate NAD⁺ for glycolysis.
• Lactic Acid Fermentation: In animals, pyruvate is reduced to lactate.
• Alcoholic Fermentation: In yeast, pyruvate is converted to ethanol and CO₂.

Key Concepts in Cellular Respiration

• Glucose and oxygen are consumed in the mitochondria.
• CO₂ and H₂O are produced.
• Cellular respiration produces a net of 38 ATP (theoretical maximum in eukaryotes).

Photosynthesis and Cellular Respiration Relationship

• Complementary processes: Photosynthesis converts light energy into glucose and oxygen, while cellular respiration converts glucose and oxygen into ATP.
• Interdependence: The products of one process serve as the reactants of the other.

The Two Major Parts of Photosynthesis

• Light Reactions:
  • Location: Thylakoid membranes
  • Inputs: Light, H₂O, NADP⁺, ADP + Pi
  • Outputs: O₂, ATP, NADPH
  • Key point: Light energy is used to split water, generating ATP and NADPH and releasing oxygen.
• Calvin Cycle (Dark Reactions):
  • Location: Stroma
  • Inputs: ATP, NADPH, CO₂
  • Outputs: Glucose (C₆H₁₂O₆)
  • Key point: CO₂ is converted into glucose using the ATP and NADPH produced in the light reactions.

This quiz explores the differences between anabolic and catabolic pathways in biochemistry. It covers topics such as energy flow, free energy, spontaneity, and enzyme function. Test your understanding of these fundamental biochemical concepts.