Glycolysis I

This course is part of a series taught by Kevin Ahern at Oregon State University on General Biochemistry. For more information about online courses go to http://ecampus.oregonstate.edu/

1. Glycolysis, the breakdown of glucose, is a catabolic pathway involving oxidation and yields ATP energy. Gluconeogenesis, the synthesis of glucose, is an anabolic pathway that involves reduction and requires ATP and ATP.. There are 10 reactions in glycolysis. Students should know structures of fructose and glucose compounds, glyceraldehyde-3-phosphate, 1,3 BPG, all enzyme names, all molecule names, and reactions I described where the Delta G zero prime is strongly positive, or strongly negative.

2. Note that glycolysis has three phases - an energy investment phase, a molecular rearrangement phase, and an energy realization phase where ATP is made.

3. In reaction #1 of glycolysis, hexokinase catalyzes transfer of phosphate to glucose from ATP, forming G6P. Thus, this step uses ATP, which provides the energy necessary for the reaction to proceed. It is an example of an energy-coupled reaction and the Delta G zero prime is strongly negative, thanks to the ATP hydrolysis.

4. Hexokinase changes shape as it binds to glucose. This property is consistent with that of an induced fit of an enzyme in the process of catalysis.

5. Reaction #2 of glycolysis is catalyzed by phosphoglucoisomerase. In it, G6P is converted to F6P. The Delta G zero prime for the reaction is close to zero. Note than a linear intermediate is formed in the process.

6. Reaction #3 is the primary regulatory reaction of glycolysis. It is catalyzed by phosphofructokinase (PFK). Note that this reaction also requires ATP. PFK is the most important regulatory enzyme for glycolysis. The molecule made in the process, F1,6BP, is a high energy molecule and the energy in the molecule is needed in the next reaction. The reaction is another example of an energy-coupled reaction and the Delta G zero prime is strongly negative, thanks to the ATP hydrolysis.

7. Reaction #4 is catalyzed by aldolase. It has a strongly positive Delta G zero prime. In the cell, however, the reaction is pulled by reactions ahead of it (which remove products) and pushed by reactions behind it (which increase amounts of reactants), making the Delta G favorable (negative). The products of this reaction are G3P and DHAP.

8. The energy barrier of reaction 4 is overcome by 'pushing' (increasing concentration of reactatnts) and 'pulling' (decreasing concentration of products) of the reaction.

9. Reaction #5 is catalyzed by the 'perfect' enzyme known as triose phosphate isomerase. The reason the enzyme operates so fast is to prevent accumulation of a toxic intermediate. The product of the reaction is G3P. The Delta G zero prime is close to zero, so this reaction is readily reversible. Everything after this step has two molecules of each.

10. Reaction 6 is the only oxidation in glycolysis. It is catalyzed by glyceraldehyde-3-phosphate dehyrogenase. The energy of the oxidation is used to put phosphate onto the acid produced by the oxidation. The products are NADH and 1,3 BPG. The latter has high energy (higher than ATP).

11. Reaction 7 produces 3PG and ATP, since the phosphate on 1,3BPG is transferred onto ADP. This enzyme is phosphoglycerate kinase.

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