In-Depth Metabolism Notes

Metabolism Notes

Overview of Metabolism

• Two main types of reactions:
  • Catabolic Reactions: Break down large, complex molecules to provide energy and smaller molecules.
  • Anabolic Reactions: Use ATP energy to build larger molecules.

Learning Goal (22.1)

• Understand the three stages of catabolism, the structure of ATP, and ATP's role in metabolic processes.

Stages of Catabolism

1. Stage 1 - Digestion and Hydrolysis

   • Large food molecules are broken down into smaller ones.
   • These smaller molecules enter the bloodstream.

2. Stage 2 - Degradation

   • Within cells, molecules are degraded into two- and three-carbon compounds.

3. Stage 3 - Oxidation

   • Small molecules undergo oxidation in the citric acid cycle.
   • This stage produces ATP energy via the electron transport chain.

Cell Structure for Metabolism

• Eukaryotic Cells:
  • Contain a nucleus that holds DNA.
  • Cell Components:
  • Cell Membrane: Encases the cell and facilitates communication.
  • Cytosol: Fluid part of the cytoplasm containing enzymes for chemical reactions.
  • Lysosome: Contains enzymes that digest and recycle structures within the cell.
  • Mitochondrion: Site of ATP synthesis via energy-producing reactions.
  • Nucleus: Contains DNA for replication and protein synthesis.
  • Ribosome: Site for protein synthesis using mRNA templates.

ATP (Adenosine Triphosphate)

• Structure of ATP: Composed of:

  • Base (adenine)
  • Ribose sugar
  • Three phosphate groups

• Function: ATP hydrolyzes to form ADP and AMP with a release of energy, essential for cellular processes.

Hydrolysis of ATP Yields Energy

• ATP Hydrolysis Reaction:
  • ATP → ADP + Pi + 7.3 kcal (31 kJ)
• ADP Hydrolysis Reaction:
  • ADP → AMP + Pi + 7.3 kcal (31 kJ)

Coenzymes in Metabolic Pathways (22.2)

• Learning Goal: Understand important coenzymes and their functions.

Oxidation and Reduction

• Oxidation: Loss of hydrogen or electrons, or increase in bonds to oxygen.
• Reduction: Gain of hydrogen ions and electrons, or decrease in bonds to oxygen.
• Coenzymes transport hydrogen ions and electrons in metabolic reactions.

Coenzyme NAD+ (Nicotinamide Adenine Dinucleotide)

• Structure: Derived from niacin, attached to ribose and ADP.
• Function: Integral in dehydrogenation reactions that produce carbon–oxygen double bonds.
• Reduces in reactions, gaining hydrogen ions/electrons.

Coenzyme NADP+

• Similar to NAD+ but involved in anabolic reactions (e.g., lipid synthesis).
• Reduced to form NADPH.

Coenzyme FAD (Flavin Adenine Dinucleotide)

• Structure: Contains riboflavin and ADP.
• Function: Participates in establishing carbon-carbon double bonds.
• Reduced to FADH2 during reactions that involve hydrogen.

Coenzyme A

• Structure: Derived from ADP and pantothenic acid with an -SH group.
• Function: Prepares small acyl groups for enzymatic reactions and forms acetyl-CoA, a high-energy thioester.

Practice Questions

• Match the following coenzymes to their functions:

  1. NAD+
  • A. Coenzyme used in oxidation of carbon-oxygen bonds.
  1. FAD
  • D. Contains riboflavin.
  1. NADH + H+
  • E. The coenzyme after C = O bond formation.
  1. FADH2
  • B. Reduced form of flavin adenine dinucleotide.
  1. Coenzyme A
  • C. Used to transfer acetyl groups.

• Hydrolysis and energy relationships of ATP and ADP, focusing on energy yield in kcal.