Transcript Glycolysis - Study in Universal Science College

Glycolysis
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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.
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
Significance of Glycolysis
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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.
Glycolysis under anaerobic condition
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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
Reactions of Glycolysis (An overview)
The First Stage of Glycolysis
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Called as Preparatory phase, which involves phosphorylation of
glucose and its conversion to glyceraldehyde - 3 - phosphate
The Second Stage of Glycolysis
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Called as pay off phase which involves oxidative conversion of
glyceraldehyde - 3 - phosphate to pyruvate and coupled to the
formation of ATP and NADH
Fate of Pyruvate
Glucose
glycolysis
Anaerobic condn
2 Pyruvate
2CO2
Anaerobic condn
aerobic condn
2 Ethanol + 2 CO2
(in yeast)
2 Lactate
2 Acetyl CoA
citric acid cycle
4 CO2 + 4 H2O
(animal, plant, and mos under aerobic conditions)
(in contracting
muscle, RBCs)