MCB 2000 Exam 4

• Fundamental needs that require energy in a cell

  • Mechanical work of movement
  • Active transport of molecules across membranes
  • Biosynthesis of biomolecules and new cells
• Metabolism


  Series of linked reactions that convert a specific reactant into a specific product
• Intermediary metabolism


  Entire set of cellular metabolic reactions
• ATP

  Adenosine triphosphate
• ATP


  • Energy is derived from fuels or light and converted into ATP
  • Contains 2 phosphoanhydride linkages
  • Kinetically stable, thermodynamically unstable
• Kinetically stable

  ATP does not spontaneously hydrolyze or break down quickly
• Thermodynamically unstable


  ATP has a high potential energy that can be released through hydrolysis
• Energy released via ATP hydrolysis is -30.5 kJ/mol
• ATP formation

  1. Chemotrophs: ADP and Pi form ATP when fuel molecules are oxidized

  2. Autotrophs: ATP is formed when light is trapped
• Phosphoryl-transfer potential


  • Tracks the ability of different organic molecules to transfer a phosphoryl group to water
  • High in ATP
  • Charge repulsions
  • Resonance stabilization
  • Increase in entropy
  • Stabilization of ADP and Pi by hydration
• Catabolic pathways


  • Synthesize ATP or ion gradients
  • Combust carbon fuels
  • Break down molecules
• Anabolic pathways


  • Use ATP and reducing power to synthesize large biomolecules
  • Create molecules
• Amphibolic pathways


  • When a pathway is both catabolic or anabolic
  • Example: TCA Cycle
• For a thermodynamically unfavorable reaction to occur in a metabolic pathway, it can be coupled with a more favorable reaction
• The oxidation of carbon fuels is an important source of cellular energy
• Oxidation state of a carbon atom

  The more reduced a carbon atom is, the more free energy is released upon oxidation
• Activated carriers

  • A small number of recurring activated carriers transfer activated groups in many metabolic pathways
  • Transfer is highly exergonic
  • Very kinetically stable and can be regulated by enzymes
  • Often derived from vitamins
• Energy charge


  • Depends on the relative amounts of ATP, ADP, AMP
  • Fluctuates over time
  • Can range from 0 to 1
  • High energy charge inhibits catabolic (ATP-generating) pathways and stimulates anabolic (ATP utilizing) pathways
• Glycolysis


  1. Investment phase: Steps 1-5

  2. Yield phase: Steps 6-10
• Glycolysis steps


  • Substrates
  • Enzymes
  • Products
• Fermentation


  • ATP generating pathways in which electrons are removed from one organic compound and passed to another organic compound
  • Allows NAD+ to be regenerated (oxidized) and reused from NADH
• Alcoholic (ethanol) fermentation


  1. Glucose forms 2 molecules of ethanol

  2. Enzyme: alcohol dehydrogenase
• Lactic acid fermentation


  1. NADH is oxidized by converting pyruvate to lactate

  2. Conversion of glucose into 2 molecules of lactate

  3. Enzyme: lactate dehydrogenase
• Glucose + 2 Pi + 2 ADP → 2 lactate + 2 ATP + 2H20
• Control sites in glycolytic pathway

  • Step 1: Hexokinase
  • Step 3: PFK (phosphofructokinase)
  • Step 10: Pyruvate kinase
• Glycolysis regulation in muscle

  • Primarily regulated by energy charge of the cell
  • Hexokinase, PFK, and pyruvate kinase are allosterically regulated
• Glycolysis regulation in liver

  • Hexokinase regulated by glucose 6-phosphate
  • PFK regulated by citrate and fructose 2,6-bisphosphate
  • Pyruvate kinase regulated by allosteric and covalent modification
• Glycolysis in muscle is primarily regulated by energy charge
• Liver's role in glycolysis regulation

  • Liver is a primary site for biosynthesis
  • Regulated by need to maintain blood glucose levels
  • Hexokinase vs glucokinase
  • PFK regulated by citrate and fructose 2,6-bisphosphate
  • Pyruvate kinase regulated by phosphorylation
• Conversion of fructose and galactose into glycolytic intermediates

  1. Galactose enters as glucose 6-phosphate

  2. Fructose: Most tissues - directly phosphorylated by ketohexokinase

  3. Liver - metabolized by the fructose 1-phosphate pathway
• Gluconeogenesis


  • The synthesis of glucose from pyruvate
  • Major site: Liver
  • Also occurs in the kidney
• Gluconeogenesis is especially important during fasting or starvation
• Noncarbohydrate precursors for gluconeogenesis

  • Pyruvate
  • Carbon skeletons of some amino acids
  • Glycerol (derived from the hydrolysis of triacylglycerols)
• Gluconeogenesis vs glycolysis


  • Not a simple reversal of glycolysis
  • 3 irreversible steps of glycolysis must be bypassed
  • Unique reactions: Conversion of pyruvate to phosphoenolpyruvate, Conversion of fructose 1,6-bisphosphate to fructose 6-phosphate, Conversion of glucose 6-phosphate to glucose
• Liver's role in gluconeogenesis

  • The final step of gluconeogenesis only occurs in the liver
  • Generation of free glucose is an important control point
  • The liver is able to perform gluconeogenesis at a significant rate
• 6 high-transfer-potential phosphoryl groups are spent in synthesizing glucose from pyruvate in gluconeogenesis
• Reciprocal regulation of glycolysis and gluconeogenesis

  • Within a cell, one pathway is relatively inactive while the other is highly active
  • Glycolysis will predominate when glucose is abundant and gluconeogenesis will be highly active when glucose is scarce
  • Energy charge determines which pathway will be more active
• Role of fructose 2,6-bisphosphate in glycolysis/gluconeogenesis regulation

  • Fructose 2,6-bisphosphate stimulates phosphofructokinase (PFK), inhibits fructose bisphosphatase
  • Activity is modulated by glucagon
  • Fructose 2,6-bisphosphate is made when glucose is abundant, broken down when glucose is low
• Cori cycle


  • Series of reactions between muscle and liver that display interorgan cooperation
  • Lactate is produced by muscle and released into blood
  • Lactate enters liver, undergoes gluconeogenesis to form glucose
  • Glucose enters blood and travels back to muscle, undergoes glycolysis