glycolysis

(noun)

the cellular metabolic pathway of the simple sugar glucose to yield pyruvic acid and ATP as an energy source

Related Terms

Examples of glycolysis in the following topics:

  • Outcomes of Glycolysis

    • One glucose molecule produces four ATP, two NADH, and two pyruvate molecules during glycolysis.
    • Glycolysis starts with one molecule of glucose and ends with two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH .
    • Instead, glycolysis is their sole source of ATP.
    • Thus, pyruvate kinase is a rate-limiting enzyme for glycolysis.
    • Describe the energy obtained from one molecule of glucose going through glycolysis

  • Importance of Glycolysis

    • Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism.
    • Glycolysis is the first pathway used in the breakdown of glucose to extract energy.
    • Glycolysis is the first of the main metabolic pathways of cellular respiration to produce energy in the form of ATP .
    • Overall, the process of glycolysis produces a net gain of two pyruvate molecules, two ATP molecules, and two NADH molecules for the cell to use for energy.
    • Glycolysis is the first pathway of cellular respiration that oxidizes glucose molecules.

  • The Energy-Releasing Steps of Glycolysis

    • In the second half of glycolysis, energy is released in the form of 4 ATP molecules and 2 NADH molecules.
    • So far, glycolysis has cost the cell two ATP molecules and produced two small, three-carbon sugar molecules.
    • 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.
    • If NAD+ is not available, the second half of glycolysis slows down or stops.
    • The second half of glycolysis involves phosphorylation without ATP investment (step 6) and produces two NADH and four ATP molecules per glucose.

  • The Energy-Requiring Steps of Glycolysis

    • In the first half of glycolysis, energy in the form of two ATP molecules is required to transform glucose into two three-carbon molecules.
    • The first step in glycolysis is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars.
    • In the second step of glycolysis, an isomerase converts glucose-6-phosphate into one of its isomers, fructose-6-phosphate.
    • The fourth step in glycolysis employs an enzyme, aldolase, to cleave 1,6-bisphosphate into two three-carbon isomers: dihydroxyacetone-phosphate and glyceraldehyde-3-phosphate.
    • The first half of glycolysis uses two ATP molecules in the phosphorylation of glucose, which is then split into two three-carbon molecules.

  • Breakdown of Pyruvate

    • After glycolysis, pyruvate is converted into acetyl CoA in order to enter the citric acid cycle.
    • In order for pyruvate, the product of glycolysis, to enter the next pathway, it must undergo several changes to become acetyl Coenzyme A (acetyl CoA).
    • This step proceeds twice for every molecule of glucose metabolized (remember: there are two pyruvate molecules produced at the end of glycolysis); thus, two of the six carbons will have been removed at the end of both of these steps.

  • Control of Catabolic Pathways

    • Enzymes, proteins, electron carriers, and pumps that play roles in glycolysis, the citric acid cycle, and the electron transport chain tend to catalyze non-reversible reactions.
    • The control of glycolysis begins with the first enzyme in the pathway, hexokinase .
    • Phosphofructokinase is the main enzyme controlled in glycolysis.
    • The last step in glycolysis is catalyzed by pyruvate kinase.
    • The glycolysis pathway is primarily regulated at the three key enzymatic steps (1, 2, and 7) as indicated.

  • ATP Yield

    • The process of glycolysis only produces two ATP, while all the rest are produced during the electron transport chain.
    • The NADH generated from glycolysis cannot easily enter mitochondria.
    • Moreover, the five-carbon sugars that form nucleic acids are made from intermediates in glycolysis.
    • Certain nonessential amino acids can be made from intermediates of both glycolysis and the citric acid cycle.
    • Glycolysis on the left portion of this illustration can be seen to yield 2 ATP molecules, while the Electron Transport Chain portion at the upper right will yield the remaining 30-32 ATP molecules under the presence of oxygen.

  • Connecting Lipids to Glucose Metabolism

    • Glycerol can be phosphorylated to glycerol-3-phosphate, which continues through glycolysis.

  • Acetyl CoA to CO2

    • Acetyl CoA links glycolysis and pyruvate oxidation with the citric acid cycle.

  • ATP: Adenosine Triphosphate

    • In the very first steps of cellular respiration, glucose is broken down through the process of glycolysis.
    • Fructose is a necessary intermediate for glycolysis to move forward.