Name: glycolysis: atp and nadh output
Uploaded: 2023-04-30T10:41:21.000Z
Duration: 1 min 25 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.8

Glycolysis: Pay-off Phase

Glycolysis is divided into two phases &#8212; the energy utilizing, preparatory phase and the energy releasing, pay-off phase.
The pay-off phase begins when 3-carbon G3P molecules are catabolized by the enzyme glyceraldehyde phosphate dehydrogenase to produce two molecules of 1,3-bisphosphoglycerate, simultaneously, producing two molecules of NADH.
Enzyme phosphoglycerate kinase then dephosphorylates 1,3-bisphosphoglycerate into two molecules of 3-phosphoglycerate while yielding two ATP molecules.
Thereafter, phosphoglycerate mutase converts 3-phosphoglycerate into 2-phosphoglycerate, which is further cleaved by enolase to produce two molecules of phosphoenolpyruvate or PEP.
Finally, another enzyme pyruvate kinase dephosphorylates PEP into pyruvate, yielding two more ATP molecules. Thus, the second phase of glycolysis produces four ATP and two NADH.
As two ATP are utilized during the first phase, the net results of glycolysis are two molecules, each of ATP, pyruvate, and NADH.

glycolysis: pay-off phase

So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules. These molecules will proceed through the second half of the pathway, and sufficient energy will be extracted to pay back the two ATP molecules used as an initial investment and produce a profit for the cell of two additional ATP molecules and two even higher-energy NADH molecules.
Step 1 - 5: Glycolysis Preparatory Phase
The first phase of glycolysis has 5 steps where the glucose is broken down into two three-carbon sugar molecules. In the next five steps of the pay-off phase, these carbon molecules are further metabolized to produce ATP and NADH.
Step 6. The sixth step in glycolysis oxidizes the sugar (glyceraldehyde 3-phosphate), extracting high-energy electrons, which are picked up by the electron carrier NAD+, producing NADH. The sugar is then phosphorylated by adding a second phosphate group, producing 1,3-bisphosphoglycerate. Note that the second phosphate group does not require another ATP molecule.
Here again, is a potential limiting factor for this pathway. The continuation of the reaction depends upon the availability of the oxidized form of the electron carrier, NAD+. Thus, NADH must be continuously oxidized back into NAD+ to keep this step going. If NAD+ is not available, the second half of glycolysis slows down or stops. If oxygen is available in the system, the NADH will be oxidized readily, though indirectly, and the high-energy electrons from the hydrogen released in this process will be used to produce ATP. In an environment without oxygen, an alternate pathway (fermentation) can provide the oxidation of NADH to NAD+.
Step 7. In the seventh step, catalyzed by phosphoglycerate kinase, 1,3-bisphosphoglycerate donates a high-energy phosphate to ADP, forming one molecule of ATP. (This is an example of substrate-level phosphorylation.) A carbonyl group on the 1,3-bisphosphoglycerate is oxidized to a carboxyl group, and 3-phosphoglycerate is formed.
Step 8. In the eighth step, the remaining phosphate group in 3-phosphoglycerate moves from the third carbon to the second carbon, producing 2-phosphoglycerate (an isomer of 3-phosphoglycerate). The enzyme catalyzing this step is a mutase (an isomerase).
Step 9. Enolase catalyzes the ninth step. This enzyme causes 2-phosphoglycerate to lose water from its structure; this is a dehydration reaction, resulting in the formation of a double bond that increases the potential energy in the remaining phosphate bond and produces phosphoenolpyruvate (PEP).
Step 10. The last step in glycolysis is catalyzed by the enzyme pyruvate kinase (the enzyme, in this case, is named for the reverse reaction of pyruvate&#39;s conversion into PEP) and results in the production of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid (or its salt form, pyruvate). Many enzymes in enzymatic pathways are named for the reverse reactions since the enzyme can catalyze both forward and reverse reactions (these may have been described initially by the reverse reaction that takes place in vitro, under nonphysiological conditions).
This text is adapted from <a href="https://openstax.org/books/biology-2e/pages/7-2-glycolysis">Openstax, Biology 2e, Section 7.2: Glycolysis</a>

So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules. These molecules will proceed through the ...

Education

JoVE Core

Cell Biology

Unit 1

Introduction to Metabolism

KEY TERMS AND CONCEPTS

glycolysis: atp and nadh output

The pay-off phase of glycolysis turns the two three-carbon sugar molecules into ATP, NADH, and pyruvate. By this stage, the cell has already spent two ATP molecules. The remaining reactions recover that investment and add two more ATP molecules and two high-energy NADH molecules.

The sixth step oxidizes glyceraldehyde 3-phosphate, a three-carbon sugar made earlier in glycolysis. High-energy electrons are transferred to NAD+, which becomes NADH. A second phosphate group is then added to form 1,3-bisphosphoglycerate, and this addition does not require another ATP molecule.

This step depends on a supply of NAD+, so it can slow down or stop if NAD+ is not available. To keep glycolysis moving, NADH must be oxidized back to NAD+. When oxygen is present, this happens readily, although indirectly, and the released electrons help drive ATP production. Without oxygen, fermentation can regenerate NAD+ and allow glycolysis to continue.

In step 7, phosphoglycerate kinase transfers a high-energy phosphate from 1,3-bisphosphoglycerate to ADP. This makes one ATP by substrate-level phosphorylation. The remaining molecule becomes 3-phosphoglycerate, and a carbonyl group is oxidized to a carboxyl group.

Step 8 shifts the phosphate group on 3-phosphoglycerate from carbon 3 to carbon 2. This produces 2-phosphoglycerate, which is an isomer of 3-phosphoglycerate. The enzyme for this step is a mutase, which is a type of isomerase.

In step 9, enolase removes water from 2-phosphoglycerate. This dehydration reaction forms a double bond and creates phosphoenolpyruvate, or PEP. The new structure increases the potential energy in the remaining phosphate bond.

The final step is catalyzed by pyruvate kinase and produces a second ATP by substrate-level phosphorylation. It also forms pyruvic acid, or pyruvate. The enzyme is named for the reverse reaction, since many pathway enzymes are named that way and can work in both directions.

Glycolysis: ATP and NADH Output

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Glycolysis: ATP and NADH Output | JoVE K12

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Glycolysis: ATP and NADH Output

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