L29: Metabolic Pathways and Glycolysis

• What was the start of biochemistry?

  The study of metabolism
• What essential process ceases at death?

  Respiration
• What can some cells, like yeast, ferment in the absence of oxygen?

  Sugar to ethanol and CO₂
• What did Manàsseina observe about fermentation?

  It was an enzymatic process
• What is glycolysis also known as?

  Embden-Meyerhof pathway
• What is the process of dialysis in studying yeast extracts?

  • Yeast lysate is placed in a cellophane bag and stirred in buffer.
  • Big molecules remain in the bag while small molecules diffuse into the buffer.
  • "Zymase" and "Cozymase" are inactive in the dialysate.
  • Activity is restored by adding dialysate, indicating both small and large molecules are involved.
• What is the definition of enzymic cofactors and coenzymes?

  A non-protein substance required for catalytic activity of some enzymes
• What are examples of inorganic cofactors?

  Metal ions such as Mg²⁺, Zn²⁺, and Mn²⁺
• What did Harden and Young conclude about inorganic phosphate in glycolysis?

  It is a limiting factor
• What are the advantages of homogenizing cells for studying enzymes?

  It allows study of a purified enzyme in isolation under defined conditions
• What is the in vivo approach in studying metabolism?

  It looks at cells or organisms to reflect the whole system
• Why do we focus on glucose metabolism?

  It is central to our energy metabolism and creates building blocks for other molecules
• What are the three stages of energy metabolism?

  1. Stage I: Large to smaller molecules, no useful energy production
  2. Stage II: Conversion of products to Acetyl-CoA, small amount of ATP produced
  3. Stage III: Acetyl-CoA to CO₂, majority of ATP produced
• Which statement about metabolic pathways is FALSE?

  Anabolic pathways are simply a reversal of catabolic pathways
• How does respiration differ from combustion?

  Respiration is a multistep pathway that conserves energy
• What are the six key types of reactions in metabolic pathways?

  1. Redox reactions: Transfer of electrons (e.g., formation of NADH)
  2. Group transfer: Transfer of functional groups (e.g., ATP production)
  3. Hydrolysis: Cleavage of bonds using water (e.g., peptide bonds)
  4. Addition/removal of functional groups: (e.g., fumarate to malate)
  5. Isomerisation: Rearrangement of atoms (e.g., G-6-P to F-6-P)
  6. Ligations: Formation of covalent bonds (e.g., CO₂ and pyruvate to oxaloacetate)
• What are metabolic crossroads and their significance?

  • Common intermediates like Glucose-6-P and Pyruvate.
  • Key steps are often irreversible and serve as control points.
  • Anabolic reactions cannot simply reverse catabolic reactions.
• What is the role of key cofactors in energy metabolism?

  They carry out a wide range of metabolic tasks
• What is NAD⁺ derived from?

  Niacin/vitamin B₃
• What key questions should be asked about metabolic pathways?

  Where it occurs, its structure, entry points, end products, and regulation
• What is glycolysis?

  A series of reactions starting with glucose and ending with pyruvate, resulting in a small gain of ATP
• What are the key features of glycolysis?

  It is anaerobic, splits glucose to pyruvate, and occurs in the cytosol
• What are the key steps in glycolysis?

  1. Investment stage: 2 ATP used, phosphorylation keeps intermediates in the cell.
  2. Payout stage: 4 ATP produced, 2 NADH produced, requires NAD⁺ and Pi.
  3. Net gain of 2 ATP per glucose.
• What determines the control of glycolysis?

  Steps with large negative ΔG are often regulatory points
• Which statement about large negative ΔG in glycolysis is false?

  Large negative ΔG means the reaction is slow
• What is the significance of strongly negative ΔG for steps 1, 3, and 10 in glycolysis?

  It pushes glycolysis forward
• Why is step 3 considered the main regulatory point for glycolysis?

  It is a key control point in the pathway
• What are the control mechanisms in glycolysis?

  • HK: Feedback inhibition
  • PFK: Regulated by energy levels (AMP/ATP) and metabolic intermediates
  • PK: Feedforward activation
• Why is glycolysis important for muscle cells?

  It generates energy (ATP) for muscle use
• How does glycolysis function in the liver?

  It generates intermediates for biosynthesis and regulates blood glucose levels
• How do other dietary sugars fit into glycolysis?

  • Galactose: Converted to glucose-1-P and enters glycolysis.
  • Fructose: Cleaved and enters glycolysis after the main regulatory step.
• What is galactosemia?


  It is a condition where the body cannot break down galactose
• How does fructose enter glycolysis?

  Fructose enters at the second stage of glycolysis after the main regulatory step
• What unique ability does the naked mole-rat have regarding fructose?

  It can survive on fructose
• What is the overview of glycolysis and its intermediates?

  • Glucose → Glucose-6-P → Pyruvate → Lactate → Acetyl-CoA
  • Involves other sugars like Galactose and Fructose.
• What are the key points to remember about glycolysis?

  • Occurs in the cytosol.
  • It is a linear pathway.
  • Main entry points: Glucose and G-6-P.
  • End product: Pyruvate.
  • Linked to citric acid cycle and fermentation.
  • Key control points: Steps 1, 3, and 10.
  • Regulation mainly by PFK.