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  • Biological organisms require energy to survive.

  • Glycolysis is one of the pathways cells use to transform sugars like

  • glucose into biochemical energy in the form of ATP.

  • In the cytosol of the cell,

  • glycolysis converts glucose into pyruvate,

  • through a series of 10 enzymatic reactions.

  • This process produces ATP,

  • along with other products, such as NADH,

  • that can be used later to produce even more ATP for the cell.

  • Let's watch as these enzymes oxidize

  • one glucose molecule into two pyruvate molecules.

  • First, a kinase reaction adds a phosphate onto glucose

  • to form glucose-6-phosphate.

  • This is one of two energy consumption steps

  • and is an irreversible reaction.

  • Next, an isomerase reaction converts glucose-6-phosphate

  • into fructose-6-phosphate

  • by rearranging covalent bonds.

  • Another kinase removes a phosphate group from ATP

  • and gives it to fructose-6-phosphate

  • to form fructose-1,6-bisphosphate.

  • This is the second energy consumption step

  • and is an irreversible reaction.

  • In the fourth step of glycolysis,

  • a lyase reaction splits the 6-carbon

  • fructose-1,6-bisphosphate

  • into two 3-carbon sugars,

  • glyceraldehyde-3-phosphate

  • and dihydroxyacetone phosphate.

  • The dihydroxyacetone phosphate is rearranged by another isomerase

  • to form a second glyceraldehyde-3-phosphate.

  • At this point in glycolysis,

  • glucose has been metabolized into two glyceraldehyde-3-phosphates,

  • and two ATPs have been consumed.

  • The next five steps of glycolysis are the energy producing phase.

  • In step six,

  • both glyceraldehyde-3-phosphates are oxidized

  • to 1,3-bisphosphoglycerate

  • by a dehydrogenase.

  • This step produces one NADH

  • for each oxidized glyceraldehyde-3-phosphate

  • for a total of two NADHs.

  • These NADHs are later used to produce more ATP for the cell.

  • In step seven, a kinase transfers a phosphate

  • from 1,3-bisphosphoglycerate to ADP

  • to form ATP and 3-phosphoglycerate.

  • This step is reversible even though ATP is formed.

  • The next step involves a mutase reaction

  • that moves the phosphate on the

  • third carbon of 3-phosphoglycerate

  • to the second carbon position

  • to form 2-phosphoglycerate.

  • In step nine, a lyase reaction removes water

  • from 2-phosphoglycerate

  • to form phosphoenolpyruvate.

  • In the final step of glycolysis,

  • a kinase reaction removes the phosphate group

  • from phosphoenolpyruvate

  • and donates it to ADP

  • to form ATP and pyruvate.

  • Like reactions one and three,

  • this step is irreversible.

  • At this point, two pyruvate molecules,

  • four ATPs,

  • and two NADHs are formed

  • for each glucose

  • that was broken down in glycolysis.

  • The pyruvates and NADHs

  • could be used in aerobic respiration to produce more energy for the cell.

  • Here we depict glycolysis as a closed process.

  • But in cells, substrates produced by other reactions

  • can enter glycolysis at different points.

  • For example,

  • when an animal breaks down glycogen,

  • glucose 6-phosphate is produced

  • and can then enter the glycolysis pathway at the second step.

  • Importantly, this means one less ATP is required

  • for the pathway because the first ATP consuming step is skipped.

  • Other sugars can also enter the glycolysis

  • pathway at different points,

  • each having a different effect

  • on the net number of ATPs

  • that are produced by glycolysis.

  • These ATPs are important energy molecules

  • required for many biochemical pathways

  • and ultimately life itself.

  • Glycolysis is a major contributor

  • to the pool of ATP used in these pathways,

  • pathways that are essential

  • to the survival of biological organisms.

Biological organisms require energy to survive.

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B2 H-INT glycolysis phosphate glucose step reaction fructose

Glycolysis: The Reactions

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    wshuang999   posted on 2014/11/24
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