Glycolysis

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Glycolysis

• Glycolysis ( Greek ? glykys sweet lysis
  splitting) involves the breakdown of glucose
  molecules through a series of reactions catalyzed
  by a set of enzymes such that a 6 C sugar forms
  a 3 C compound.

• Significance of Glucose in biological systems
• A major fuel source of the body hence occupies a
  central position in metabolism
• Most of the tissues require some amt. of glucose
  for their proper functions however in brain the
  requirement is significant and erythrocytes which
  lack mitochondria rely on glucose as their
  metabolic fuel carrying out anaerobic glycolysis.
• In higher forms of life, glucose has three
  different fates.

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Major pathway of glucose utilization in higher
forms

• Glycogen
• (or starch, sucrose)
• GLUCOSE
• Ribose sugar Pyruvate, lactate
• Fate of glucose in the body
• may be stored in a complex form as glycogen
• oxidized to pyruvate by glycolysis or
• oxidized to pentose by Pentose phosphate pathway

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Significance of Glycolysis

• It is the principal route for glucose metabolism
  and the metabolism of other hexoses (fructose,
  galactose)
• Its ability to function under anaerobic condition
  is of significance, as it allows skeletal muscle
  to function and survive under anoxic episodes by
  providing ATP
• However certain tissue like the heart muscle is
  adapted for aerobic performance, and hence
  possesses low glycolytic activity and survival
  rate under ischemic conditions
• In pathological conditions like fast growing
  cancer cells glycolysis proceeds at a higher rate
  than the requirement of TCA cycle, due which the
  large amts. of pyruvate formed gets converted to
  lactate producing a local acidic environment in
  the tumors.

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Glycolysis under anaerobic condition

• Involves anaerobic degradation of glucose and is
  also termed as Fermentation in general
• During muscle contraction in anaerobic medium,
  lactate appears as the end product
• Anaerobic glycolysis however has a price, for it
  limits the amount of ATP generated per molecule
  of glucose, due which much more glucose is
  metabolized in anaerobic medium
• During anaerobic condition, mitochondrial re
  oxidation of NADH (formed during glycolysis) is
  impaired, which is then reoxidized to NAD by
  reducing pyruvate to lactate.
• When oxygen is supplied, the lactate then
  disappears.
• However, in aerobic condition, pyruvate forms
  the end product being further oxidised to CO2 and
  water

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Reactions of Glycolysis (An overview)
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The First Stage of Glycolysis

• Called as Preparatory phase, which involves
  phosphorylation of glucose and its conversion to
  glyceraldehyde - 3 - phosphate

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The Second Stage of Glycolysis

• Called as pay off phase which involves oxidative
  conversion of glyceraldehyde - 3 - phosphate to
  pyruvate and coupled to the formation of ATP and
  NADH

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Fate of Pyruvate

• Glucose
• glycolysis
• Anaerobic condn 2 Pyruvate
  Anaerobic condn
• 2CO2
  aerobic condn
• 2 Ethanol 2 CO2 2
  Lactate
• (in yeast) 2 Acetyl CoA (in
  contracting muscle, RBCs)
• citric acid cycle
• 4 CO2 4 H2O
• (animal, plant, and mos under aerobic conditions)