MB 9.2
What happens during steps 1-4 in glycolysis?
1. Hexokinase transfers a phosphate group from ATP to glucose, making it more chemically reactive. The charge on the phosphate also traps the sugar in the cell. 2. Glucose 6 phosphate is converted to its isomer, fructose 6-phosphate. 3. Phosphofructokinase transfers a phosphate group from ATP to the opposite end of the sugar, investing a second molecule of ATP. This is a key step for regulation of glycolysis. 4. Aldolase cleaves the sugar molecule into two different three-carbon sugars (isomers)
What happens during steps 5-7 in glycolysis?
5. Isomerase catalyzes the reversible conversion between the two isomers. This reaction never reaches equilibrium. Glyceraldehyde 3 phosphate is used as a substrate of the next reaction (step 6) as fast as it forms. 6. Triose phosphate dehydrogenase catalyzes two sequential reactions. First, the sugar is oxidized by the transfer of electrons to NAD+, forming NADH. Second, the energy released from this exergonic redox reaction is used to attach a phosphate group to the oxidized substrate, making a product of very high potential energy. 7. The phosphate group added in the previous step is transferred to ADP in an exergonic reaction. The carbonyl group of a sugar has been oxidized to the carboxyl group (COO-) of an organic acid (3-phosphoglycerate).
What happens during steps 8-10 in glycolysis?
8. Phosphoglyceromutase is an enzyme that relocates the remaining phosphate group. 9. Enolase an enzyme causes a double bond to form in the substrate by extracting a water molecule, yielding phosphoenolpyruvate (PEP) , a compound with a very high PE. 10. The phosphate group is transferred from PEP to ADP (a second example of substrate-level phosphorylation), forming a pyruvate.
Does glycolysis occur in the presence of oxygen?
All of the carbon originally present in glucose is accounted for in the two molecules of pyruvate; no carbon is released as CO2 during glycolysis. Glycolysis occurs whether or not oxygen is present. However, if oxygen is present, the chemical energy stored in pyruvate and NADH can be extracted by pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation.
What two phases can glycolysis be divided into?
Glycolysis can be divided into two phases: energy investment and energy payoff. During this energy investment phase, the cell actually spends ATP. This investment is repaid with interest during the energy payoff phase, when ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by electrons released from the oxidation of glucose. The net energy yield from glycolysis, per glucose molecule is 2 ATP plus 2 NADH. There are about 10 steps in the glycolytic pathway.
What does the word glycolysis mean?
It means "sugar splitting," and that is exactly what happens during this pathway. Glucose, a six carbon sugar, is split into three-carbon sugars. These smaller sugars are then oxidized and their remaining atoms rearranged to form two molecules of pyruvate. (Pyruvate is the ionized form of pyruvic acid.)
During the redox reaction in glycolysis (step 6 in Figure 9.9), which molecule acts as the oxidizing agent? The reducing agent?
[9.2 - 1] NAD+ acts as the oxidizing agent in step 6, accepting electrons from glyceraldehyde 3-phosphate, which thus acts as the reducing agent.
Step 3 in figure 9.9 is a major point of regulation of glycolysis. The enzyme phosphofructokinase is allosterically regulated by ATP and related molecules. Considering the overall result of glycolysis, would you expect ATP to inhibit or stimulate activity of this enzyme? Hint: Make sure you consider the role of ATP as an allosteric regulator, not as a substrate of the enzyme.
[9.2 - 2] Since the overall process of glycolysis results in the net production of ATP, it would make sense for the process to slow down when ATP levels have increased substantially. Thus, we would expect ATP to allosterically inhibit phosphofructokinase.
