Metabolic pathways

• How many reactions occur in Escherichia coli?

  Over 1000 reactions
• What does biochemical unity underlie?

  Diversity in metabolic reactions
• What is true about the number of types of reactions in metabolism?

  The number of types is small
• How are metabolic reactions generally characterized?

  Reactions are usually simple
• How many molecules play a central role in metabolism?

  About 100 molecules
• What are catabolic pathways responsible for?

  • Break down complex macromolecules
  • Produce common intermediates (e.g., acetyl-CoA)

  
• What do anabolic pathways do?

  • Use common intermediates (e.g., acetyl-CoA)
  • Synthesize diverse complex macromolecules
• What are the requirements for metabolic pathways?

  • Enzymes (e.g., hexokinase)
  • Metabolites (substrates, e.g., glucose)
  • Coenzymes (e.g., ATP)

  
• What do proteases degrade?

  Proteins/polypeptides
• What do DNAse and RNAse degrade?

  Nucleic acids
• What do dehydrogenases catalyze?

  Redox reactions
• What do lipases catalyze?

  Lipid hydrolysis
• What do oxidoreductases catalyze?

  Oxidation/reduction reactions
• What do transferases do?

  Transfer a functional group
• What do hydrolases catalyze?

  Hydrolysis of various bonds
• What do lyases do?

  Cleave bonds not by hydrolysis
• What do isomerases catalyze?

  Isomerization within a single molecule
• What do ligases do?

  Join two molecules with covalent bonds
• What are coenzymes?

  • Metabolites/enzyme substrates
  • Involved in various reactions
  • Transfer chemical groups
  • Example: ATP carries phosphate groups
• What is the coenzyme for Vitamin B1 (Thiamine)?

  Thiamine diphosphate
• What is the coenzyme for Vitamin B2 (Riboflavin)?

  FAD
• What is the coenzyme for Vitamin B6 (Pyroxidine)?

  Pyridoxal phosphate
• What is the coenzyme for Vitamin B3 (Nicotinic acid)?

  NAD, NADP
• What is the coenzyme for Vitamin B5 (Pantothenic acid)?

  Coenzyme A
• What is the coenzyme for Vitamin B7 (Biotin)?

  Biotin-lysine adduct
• What is the coenzyme for Folic acid?

  Tetrahydrofolate
• What is the coenzyme for Vitamin B12 (Cobalamin)?

  Methylmalonyl CoA mutase
• What are the key features of metabolic pathways?

  • Metabolic pathways are irreversible
  • Highly exergonic (large –ve ΔG)
  • Committed first step in each pathway
  • Regulated pathways
  • Defined locations in eukaryotic cells
• What are the benefits and disadvantages of organelles in metabolism?

  Benefits:

  • Compartmentalization of processes
  • High concentrations where needed
  • Linked reactions

  
  

  Disadvantages:

  • Need for transport
  • Levels of control
  • Energy required
• What do electron carriers do in metabolic processes?

  Transfer electrons in redox reactions
• What are the oxidized forms of NAD and FAD?

  NAD(P)+ and FAD+

  
• What are the reduced forms of NAD and FAD?

  NAD(P)H and FADH2

  
• What happens during the oxidation of lactate?

  Lactate loses 2 protons and electrons
• What happens during the reduction of NAD+?

  NAD+ gains 2 electrons and 1 proton
• What is the significance of the committed first step in metabolic pathways?

  It avoids equilibria in reactions
• Why are metabolic pathways often regulated at the first step?

  Other reactions can equilibrate
• What is a key feature of eukaryotic cells regarding metabolic pathways?

  Pathways have defined locations
• What is a disadvantage of compartmentalization in organelles?

  Need for transport of materials
• What is an advantage of compartmentalization in organelles?

  High concentrations where needed
• What is a disadvantage of needing energy for organelle function?

  Increased metabolic costs