Biochemistry Chapter 17 - Introduction to Metabolism

General Biochemistry: Part II (CHEM 3420)

• Course focused on Chapter 17: Introduction to Metabolism
• Developed by Dr. Koen Vercruysse, Associate Professor, Chemistry Department, Tennessee State University
• Metabolic pathways are like studying the interstate system of freeways
• Movement of biochemical molecules through pathways is like cars on the interstates
• Different pathways exist for carbohydrates, lipids, and amino acids, intersecting and redirecting based on cellular needs
• Pathways are sequences of biochemical reactions transforming one biomolecule to another
• The figure on page 3 shows a complex diagram illustrating different metabolic pathways linking various molecules (glucose, amino acids, fatty acids, nucleotides, etc.)
• The endpoint of metabolism is ATP synthesis
• ATP acts as the universal carrier of chemical energy
• All organisms use ATP to build biomolecules, cells, tissues, and replicate themselves
• Aerobic metabolism uses oxygen's reduction to water to produce energy
• Anaerobic metabolism uses other reduction reactions
• The Citric acid (Krebs) cycle is the central hub of metabolism, breaking down nutrients
• Nutrients entering the cycle lead to the output of CO2 and cofactors like NADH and FADH2 which are electron carriers crucial to ATP synthesis
• The electron transport process harnesses electrons to produce ATP
• This is a fundamental aspect of life similar to DNA-to-mRNA-to-protein processes
• Lipids are the main storage form of excess calories
• Nutrients (carbohydrates, lipids, proteins, and nucleic acids), break down to acetyl-Coenzyme A (AcCoA)
• AcCoA enters the Krebs cycle or builds fatty acids
• The making of proteins from amino acids (translation) and the making of DNA or RNA from nucleotides (replication/transcription) are not covered in detail in this course
• Different metabolic strategies exist in prokaryotic organisms
  • Aerobes: Require oxygen
  • Anaerobes: Cannot tolerate oxygen
  • Facultative anaerobes: Can switch between aerobic and anaerobic based on conditions
• Different approaches exist in all living organisms to obtain energy
  • Autotrophs: Use CO2 as the main carbon source
  • Heterotrophs: Use complex organic molecules (e.g., carbohydrates) as the carbon source
  • Phototrophs: Use sunlight as the energy source
  • Chemotrophs: Use redox reactions as the energy source
• Metabolic pathways are sequences of biochemical reactions catalyzed by specific enzymes
• Enzymes work in a chain-like fashion, with the product of one enzyme acting as the substrate for the next
• Enzymes can be organized loosely or as part of a larger complex structure
• Enzymes can be found in specific locations within the cell (e.g., cytosol, mitochondria, membranes)
• Cofactors (coenzymes and cations like Fe2+, Cu2+) are necessary for enzyme function
• Some essential cofactors, lacking in human synthesis, are obtained through diet
• Metabolic pathways can be exothermic (releasing energy) or endothermic (requiring energy)
• Metabolism consists of two main branches:
  • Anabolic (creating biomolecules)
  • Catabolic (breaking down biomolecules)
• ATP is the universal carrier of chemical energy and is composed of adenine, ribose, and phosphate groups
• Phosphate groups provide high-energy bonds
• Breakdown of ATP provides energy via hydrolysis into ADP and AMP
• Other high-energy molecules like GTP exist
• The key cofactors NAD+ and NADP+ are involved in electron transfer
• NAD+ and NADP+ bind either with NAD or NADP.
• Nicotinamide is the essential portion and cannot be synthesized in humans, a vitamin B group member
• Involved in catabolic reactions, turning electrons to ATP or for anabolic reactions (energy)
• NAD+ and NADP+ are reduced to NADH and NADPH which carry high energy electrons
• FAD (Flavin adenine dinucleotide) is another important electron carrier
• FAD captures electrons in two steps (producing the two electrons)
• FAD is crucial in the energy conversion to ATP
• Redox reactions involve electron transfer between molecules
  • Oxidation: Loss of electrons or increase in oxygen or decrease in hydrogen
  • Reduction: Gain of electrons or increase in hydrogen or decrease in oxygen
• Examples of oxidation-reduction reactions are shown to help understand how these processes operate in metabolic pathways