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CHAPTER 14 Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway…

- - - - First: Activate it by phosphorylation.
      - Second: Collect energy from the high-energy metabolites.
  - - - understanding the role of coenzymes
      - discovery of the pivotal role of ATP
      - development of methods for enzyme purification
      - inspiration for the next generations of biochemists
  - - - 4 ATP - used for energy-requiring processes within the cell
      - 2 NADH - must be reoxidized to NAD+ in order for glycolysis to continue
      - 2 pyruvate - various different fates
    - - ensure proper use of nutrients
      - ensure production of ATP only when needed
  - - - lactose: glucose and galactose
      - sucrose: glucose and fructose
      - Monosaccharides fructose, galactose, and mannose enter glycolysis at different points.
  - - - high amount of oxygen consumption to fuel gluconeogenesis
      - restores muscle glycogen stores
  - - - pyruvate decarboxylase: Mg++ and thiamine pyrophosphate
      - alcohol dehydrogenase: Zn++ and NAD+
- - - - generates energy via oxidation of glucose
      - short-term energy needs
    - - generates NADPH for use in relieving oxidative stress and synthesizing fatty acids
      - generates pentose phosphates for use in DNA/RNA biosynthesis
    - - can be stored in the polymeric form (starch, glycogen)
      - used for later energy needs
    - - used for generation of alternate carbohydrates used in cell walls of bacteria, fungi, and plants
  - - - yields good amount of energy upon oxidation• −2840 kJ/mol glucose
      - can be efficiently stored in the polymeric form
      - Many organisms and tissues can meet their energy needs on glucose only.
    - - all the amino acids
      - membrane lipids
      - nucleotides in DNA and RNA
      - cofactors needed for the metabolism
- - - - by fructose bisphosphatase-1
      - coordinately/oppositely regulated with PFK
      - cleaves phosphate with water
      - DOES NOT generate ATP
    - - by glucose 6-phosphatase
      - segregated in the endoplasmic reticulum
      - cleaves phosphate with water
      - DOES NOT generate ATP
  - - - during starvation
      - during vigorous exercise
      - can generate glucose from amino acids, but not fatty acids
  - - - sugars: pyruvate, lactate, or oxaloacetate
      - protein: from amino acids that can be converted to citric acid cycle intermediates (or glucogenic amino acids)
    - - product of fatty acid degradation is acetyl-CoA
      - cannot have a net converstion of acetyl-CoA to oxaloacetate
  - - - no ATP generated during gluconeogenesis
      - different enzymes in the different pathways
      - differentially regulated to prevent a futile cycle
- - - - reductive biosynthesis of fatty acids and steroids
      - repair of oxidative damage
    - - used in DNA and RNA synthesis
      - or synthesis of some coenzymes