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Glycolysis forum
Chemistry Explained :: Ge-Hy
Glycolysis
Glycolysis is the sequence of enzymatic reactions that oxidize the six-carbon sugar
glucose into two three-carbon compounds with the production of a small amount of
adenosine triphosphate (ATP). Glycolysis has two basic functions in the cell. First,
it metabolizes simple six-carbon sugars to smaller three-carbon compounds that are
then either fully metabolized by the mitochondria to produce carbon dioxide and a
large amount of ATP or used for the synthesis of fat for storage. Second, glycolysis
functions to produce
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Figure 1. The glycolytic pathway.
a small amount of ATP, which is essential for some cells solely dependent on that
pathway for the generation of energy.
The glycolytic pathway is nearly ubiquitous, being found in every cell of virtually all
living creatures. It is catalyzed by soluble enzymes located in the cytosol of cells.
Although the glycolytic pathway is most commonly thought of as metabolizing
glucose, other common monosaccharides such as fructose, galactose, and mannose
are also metabolized by it. The glycolytic pathway operates in both the presence
(aerobic) or absence of oxygen (anaerobic).
Figure 2. Structure of pyruvate.
The metabolism of fuel molecules in the cell can be thought of as an oxidation
process. In glycolysis, glucose is the fuel molecule being oxidized. As the glucose is
oxidized by the glycolytic enzymes, the coenzyme nicotinamide adenine dinucleotide
(NAD+) is converted from its oxidized to reduced form (NAD+ to NADH). When
oxygen is available (aerobic conditions), mitochondria in the cell can reoxidize to
NADH to NAD+. However, if either oxygen levels are insufficient (anaerobic
conditions) or mitochondrial activity is absent, NADH must be reoxidized by the cell
using some other mechanism. In animal cells, the reoxidation of NADH is
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accomplished by reducing pyruvate, the end-product of glycolysis, to form lactic
acid. This process is known as anaerobic glycolysis. During vigorous exercise,
skeletal muscle relies heavily on it. In yeast, anaerobic conditions result in the
production of carbon dioxide and ethanol from pyruvate rather than lactic acid. This
process, known as alcoholic fermentation, is the basis of wine production and the
reason why bread dough rises.
Although some cells are highly dependent on glycolysis for the generation of ATP,
the amount of ATP generated per glucose molecule is actually quite small. Under
anaerobic conditions, the metabolism of each glucose molecule yields only two ATPs.
In contrast, the complete aerobic metabolism of glucose to carbon dioxide by
glycolysis and the Krebs cycle yields up to thirty-eight ATPs. Therefore, in the
majority of cells the most important function of glycolysis is to metabolize glucose to
generate three-carbon compounds that can be utilized by other pathways. The final
product of aerobic glycolysis is pyruvate. Pyruvate can be metabolized by pyruvate
dehydrogenase to form acetyl coenzyme A (acetyl CoA). Under conditions where
energy is needed, acetyl CoA is metabolized by the Krebs cycle to generate carbon
dioxide and a large amount of ATP. When the cell does not need energy, acetyl CoA
can be used to synthesize fats or amino acids.
SEE ALSO INSULIN;
KREBS CYCLE.
Robert Noiva
Bibliography
Berg, Jeremy M.; Tymoczko, John L.; and Stryer, Lubert (2002). Biochemistry, 5th
edition. New York: W.H. Freeman.
Voet, Donald; Voet, Judith G.; and Pratt, Charlotte W. (2002). Fundamentals of
Biochemistry, updated edition. New York: Wiley.
User Contributions:
Edward L.Massaquoi,Jr
1
Sep 10, 2007 @ 9:09 am
This is important plesae send me a copy of it cuz i am studing on it
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