Glycolysis vs Gluconeogenesis
Cells take energy by the hydrolysis of ATP molecules. ATP (adenosine triphosphate) is also known as the ‘currency’ of the biological world, and it is involved in most cellular energy transactions. ATP synthesis requires cells to perform exergonic reactions. Both glycolysis and gluconeogenesis pathways have nine intermediates and seven enzyme-catalyzed reactions. The regulation of these pathways in animal cells involves one or two major control mechanisms; allosteric regulation and hormonal regulation.
What is Glycolysis?
The glycolysis or glycolytic pathway is a sequence of ten step reactions that converts one glucose molecule or any of several related sugars into two pyruvate molecules with the formation of two ATP molecules. Glycolysis pathway does not require oxygen so that it can happen in both aerobic and anaerobic conditions. All the intermediate states existent in this pathway have either 3 or 6 carbon atoms. All the reactions present in the glycolysis pathway can be put into five categories, namely, phosphoryl transfer, phosphoryl shift, isomerization, dehydration, and aldol cleavage.
The glycolysis reaction sequence can be divided into three major steps. First glucose is trapped and destabilized. Then the molecule with 6 carbon atoms is split into molecules with two or three carbon atoms. The glycolysis pathway, which does not require oxygen, is called fermentation, and it is identified in terms of the principal end-product. For example, a product of glucose fermentation in animals and many bacteria is lactate; thus called lactate fermentation. In most plant cells and yeast, the end-product is ethanol and hence called alcoholic fermentation.
What is Gluconeogenesis?
Gluconeogenesis is defined as the process of synthesizing glucose and other carbohydrates from three or four carbon precursors in living cells. Usually, these precursors are non-carbohydrate in nature; Pyruvate is the most common precursor in many living cells. Under anaerobic conditions, pyruvate is converted into lactate and it is used as the precursor in this pathway.
Mainly the gluconeogenesis is taking place in the liver and kidney. First seven reactions in the gluconeogenesis pathway occur by simple reversal of the corresponding reactions in glycolysis pathway. However, not all the reactions are reversible in the glycolysis pathway. Therefore, four bypass reactions of gluconeogenesis circumvent the irreversibility of the three glycolytic steps (Step 1, 3, and 10).
What is the difference between Glycolysis and Gluconeogenesis?
• The three essentially irreversible reactions of the glycolic pathway are circumvented in gluconeogenesis pathway by four bypass reactions.
• Gluconeogenesis is an anabolic pathway while glycolysis is a catabolic pathway.
• Glycolysis is an exergonic pathway, thus yielding two ATPs per glucose. Gluconeogenesis requires coupled hydrolysis of six phosphoanhydride bonds (four from ATP and two from GTP) in order to direct the process of glucose formation.
• Gluconeogenesis occurs mainly in the liver whereas glycolysis occurs in muscles and other various tissues.
• Glycolysis is a process of catabolizing glucose and other carbohydrates while gluconeogenesis is a process of synthesizing sugars and polysaccharides.
• First seven reactions in the gluconeogenesis pathway occur by simple reversal of the corresponding reactions in glycolysis pathway.
• Glycolysis uses two ATP molecules but generates four. Therefore, the net yielding ATPs per glucose are two. On the other hand, glyconeogenesis consumes six ATP molecules and synthesize one glucose molecule.