is a metabolic process by which glucose and other carbon sugars are converted into cellular energy
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Answer:
Explanation:
What is glycolysis?
Glycolysis is a series of reactions that extract energy from glucose by splitting it into two three-carbon molecules called pyruvates. Glycolysis is an ancient metabolic pathway, meaning that it evolved long ago, and it is found in the great majority of organisms alive today^{2,3}
2,3
start superscript, 2, comma, 3, end superscript.
In organisms that perform cellular respiration, glycolysis is the first stage of this process. However, glycolysis doesn’t require oxygen, and many anaerobic organisms—organisms that do not use oxygen—also have this pathway.
Highlights of glycolysis
Glycolysis has ten steps, and depending on your interests—and the classes you’re taking—you may want to know the details of all of them. However, you may also be looking for a greatest hits version of glycolysis, something that highlights the key steps and principles without tracing the fate of every single atom. Let’s start with a simplified version of the pathway that does just that.
Glycolysis takes place in the cytosol of a cell, and it can be broken down into two main phases: the energy-requiring phase, above the dotted line in the image below, and the energy-releasing phase, below the dotted line.
Energy-requiring phase. In this phase, the starting molecule of glucose gets rearranged, and two phosphate groups are attached to it. The phosphate groups make the modified sugar—now called fructose-1,6-bisphosphate—unstable, allowing it to split in half and form two phosphate-bearing three-carbon sugars. Because the phosphates used in these steps come from \text{ATP}ATPstart text, A, T, P, end text, two \text{ATP}ATPstart text, A, T, P, end text molecules get used up.
Simplified diagram of glycolysis.
Energy investment phase. Glucose is first converted to fructose-1,6-bisphosphate in a series of steps that use up two ATP. Then, unstable fructose-1,6-bisphosphate splits in two, forming two three-carbon molecules called DHAP and glyceraldehyde-3-phosphae. Glyceraldehyde-3-phosphate can continue with the next steps of the pathway, and DHAP can be readily converted into glyceraldehyde-3-phosphate.
Energy payoff phase. In a series of steps that produce one NADH and two ATP, a glyceraldehyde-3-phosphate molecule is converted into a pyruvate molecule. This happens twice for each molecule of glucose since glucose is split into two three-carbon molecules, both of which will go through the final steps of the pathway.
Simplified diagram of glycolysis.
Energy investment phase. Glucose is first converted to fructose-1,6-bisphosphate in a series of steps that use up two ATP. Then, unstable fructose-1,6-bisphosphate splits in two, forming two three-carbon molecules called DHAP and glyceraldehyde-3-phosphae. Glyceraldehyde-3-phosphate can continue with the next steps of the pathway, and DHAP can be readily converted into glyceraldehyde-3-phosphate.
Energy payoff phase. In a series of steps that produce one NADH and two ATP, a glyceraldehyde-3-phosphate molecule is converted into a pyruvate molecule. This happens twice for each molecule of glucose since glucose is split into two three-carbon molecules, both of which will go through the final steps of the pathway.
The three-carbon sugars formed when the unstable sugar breaks down are different from each other. Only one—glyceraldehyde-3-phosphate—can enter the following step. However, the unfavorable sugar, \text{DHAP}DHAPstart text, D, H, A, P, end text, can be easily converted into the favorable one, so both finish the pathway in the end
Energy-releasing phase. In this phase, each three-carbon sugar is converted into another three-carbon molecule, pyruvate, through a series of reactions. In these reactions, two \text{ATP}ATPstart text, A, T, P, end text molecules and one \text{NADH}NADHstart text, N, A, D, H, end text molecule are made. Because this phase takes place twice, once for each of the two three-carbon sugars, it makes four \text{ATP}ATPstart text, A, T, P, end text and two \text{NADH}NADHstart text, N, A, D, H, end text overall.
Each reaction in glycolysis is catalyzed by its own enzyme. The most important enzyme for regulation of glycolysis is phosphofructokinase, which catalyzes formation of the unstable, two-phosphate sugar molecule, fructose-1,6-bisphosphate^4
4
start superscript, 4, end superscript. Phosphofructokinase speeds up or slows down glycolysis in response to the energy needs of the cell.
Overall, glycolysis converts one six-carbon molecule of glucose into two three-carbon molecules of pyruvate. The net products of this process are two molecules of \text{ATP}ATPstart text, A, T, P, end text (444 \text{ATP}ATPstart text, A, T, P, end text produced -−minus 222 \text{ATP}ATPstart text, A, T, P, end text used up) and two molecules of \text{NADH}NADHstart text, N, A, D, H, end text.
