糖酵解- Steps, ATP generation and Significance

• Fermentation and respiration are two major strategies for energy conservation in chemoorganotrophs.
• The glycolytic pathway is a major metabolic pathway for microbial fermentation which involves the catabolism of glucose into pyruvate.
• 也称为Embden–Meyerhof–Parnas pathwayfor its major discoverers.
• Regardless of whether glucose is fermented or respired, it travels through this pathway thus it is referred to as the universal pathway of glucose catabolism.

图像来源：Quizlet Inc.

Location

糖酵解发生在大多数人体组织的细胞细胞质中。

Steps Involved in Glycolysis

• 在糖酵解中，将葡萄糖分子降解在一系列酶催化反应中，产生两个分子的碳化合物 - 丙酮酸。
• 葡萄糖通过糖酵解途径的发酵可以分为两个阶段，每个阶段都需要几个独立的酶促反应。
• Phase I comprises of “preparatory” reactions : These are not redox reactions and do notrelease energy but instead form a key intermediate of the pathway.
• 在第二阶段，发生氧化还原反应，能量保守，并形成两个丙酮酸分子。

Phase I: Energy investment phase (Preparatory phase)

• First five reactions of the pathway.
• Converts one glucose molecule to two glyceraldehyde-3- phosphate.
• Consumes two ATP.
• Includes rate-limiting step of the conversion of fructose-6-phosphate to fructose-1,6-bisphosphonate as catalyzed by phosphofructokinase.

涉及反应

1. Glucose is phosphorylated with the use of ATP by hexokinase, yielding glucose 6-phosphate.
2. 然后将6-磷酸葡萄糖异构化为6-磷酸糖糖糖异构酶。
3. Second phosphorylation leads to the production of fructose1,6-bisphosphate by phosphofructokinase 1 (PFK-1), which is the rate-limiting enzyme of glycolysis. The reaction uses 1 ATP.
4. 然后，酶醛糖酶将1,6-双磷酸果糖分裂为两个3碳分子，即3-磷酸甘油醛及其异构体二羟基乙酮磷酸，最终将其转化为3-磷酸甘油醛。

Phase II: Energy production phase (Pay-off phase)

• Converts two G3P to two pyruvate.
• Produces four ATP and two NADH.

涉及反应

1. The first redox reaction is the oxidation of glyceraldehyde 3-phosphate to 1,3 bisphosphoglyceric acid by glyceraldehyde 3-phosphate dehydrogenase using NAD + as a cofactor.
2. 1, 3-bisphosphoglyceric acid is converted to 3-phosphoglyceric acid by phosphoglycerate kinase. This reaction generates 2 ATP per glucose molecule.
3. 通过磷酸甘油酸突变酶将3-磷酸甘油酸转化为2-磷酸甘油酸。
4. 通过烯醇酶将2-磷酸甘油酸到磷酸烯醇丙酮酸（PEP）的可逆转化。
5. Regulated, irreversible reaction involving the conversion of PEP to pyruvate by pyruvate kinase. There is a net gain of 2 ATP per glucose molecule in this reaction.

ATP generation

• 在糖酵解I和II期间，两个ATP分子被消耗，four ATP分子合成。
• 因此，糖酵解中的净能量产量为two molecules of ATP葡萄糖发酵的分子。

• However, maximal ATP yield from oxidation of glucose is36 to 38 ATP.
• 通过丙酮酸脱氢酶，每个葡萄糖分子ATP的最大产量取决于糖酵解与柠檬酸周期的偶联。

Significance of Glycolysis Pathway

1. 糖酵解途径均由所有组织用于葡萄糖分解，以以ATP形式提供能量。
2. Important pathway for the production of energy especially under anaerobic conditions.
3. It is crucial for generation of energy in cells without mitochondria.
4. 它形成了其他代谢途径中间的产品。
5. 糖酵解interfaces with glycogen metabolism, the pentose phosphate pathway, the formation of amino sugars, triglyceride synthesis (by means of glycerol 3-phosphate), the production of lactate (a dead-end reaction), and transamination with alanine.

Associated Diseases:

缺乏任何糖酵解酶的线索to hemolytic anemia because RBCs depend on glycolysis for energy production and will lyse if their energy demands are not met as a result of faulty glycolysis.

参考

1. Lehninger, A. L., Nelson, D. L., & Cox, M. M. (2000). Lehninger principles of biochemistry. New York: Worth Publishers.
2. John W. Pelley，Edward F. Goljan（2011）。生物化学。第三版。费城：美国。
3. Madigan, M. T., Martinko, J. M., Bender, K. S., Buckley, D. H., & Stahl, D. A. (2015). Brock biology of microorganisms (Fourteenth edition.). Boston: Pearson.
4. Rodwell，V。W.，Botham，K。M.，Kennelly，P。J.，Weil，P。A.，＆Bender，D。A.（2015年）。哈珀的插图生物化学（第30版）。纽约，纽约：McGraw-Hill Education LLC。