1. There are six classes of reactions catalyzed by enzymes. They include Oxidation-Reduction Reactions (electrons gained/lost), Ligation Reactions (two molecules put together), Isomerization Reactions (intramolecular rearrangements), Group Transfer Reactions (movement of a part of one molecule to another molecule), Hydrolytic Reactions (breakdown reactions using water), and Lyases (breakdown reactions involving a double bond, but not using water to break the molecule down)
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, 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 two phases - an energy investment phase requiring input of ATP energy 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. I will talk more about this later.
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 is catalyzed by phosphoglycerate kinase and it includes a substrate level phosphorylation (transfer of a phosphate from a molecule directly to ADP) to make ATP.
12. Reaction #8 is catalyzed by phosphoglycerate mutase and it simply involves rearrangement of the 3PG into 2PG. The Delta G zero prime is close to zero and the direction of the reaction is driven by cellular concentrations. Note that the mutase creates as an intermediate 2,3BPG, which is the molecule hemoglobin bound to and caused it to release oxygen.
End of material for exam 2 HERE