Phosphofructokinase 1

Phosphofructokinase I.

Glycolysis is the biochemical pathway by which glucose is converted into pyruvate via fructose-1,6-bisphosphate. A sequence of ten enzymatic reactions, glycolysis generates 2 mol ATP/mol of glucose. Glycolysis is the main source of energy for most anaerobic organisms. In aerobic organisms, in addition to providing some ATP, glycolysis plays the role of transforming glucose, as well as some other sugars, into the substrate of oxidative degradation.

Glycolysis is the quintessential biochemical pathway. Glycolysis is not only important in MCAT review for itself, but also as a model for enzymatic mechanisms and their underlying organic chemistry. Additionally, glycolysis is a model for the regulation of biochemical pathways in the context of physiological integration.

WikiPremed Resources

Bioenergetics and Cellular Respiration Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Glycolysis & Pyruvate Dehydrogenase
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Be prepared to narrate the steps of oxidative metabolism from glycolysis, mobilization of pyruvate, citric acid cycle, to the electron transport system.

Understand the roles of glucose, ATP, NADH and other prominent substances in respiration and metabolism.

Be able to describe the steps of glycolysis, account for the ATP and NADH created.

Be able to identify the enzymes that are the primary control sites for glycolysis, which is the committed step, and which factors influence inhibition or promotion.

Understand the driving forces governing the respective phosphoryl transfer potentials of 1,3 bis-phosphoglycerate and phosphoenolpyruvate. Particularly, be prepared to describe the bioenergetics rationale underlying the mechanism of glyceraldehyde-3-phosphate dehydrogenase.

Understand the purpose of fermentation and describe the specific fates of pyruvic acid in yeast and active muscles respectively.

Be able to describe the mechanisms of the pyruvate dehydrogenase complex and name its coenzymes.

Understand the various feeder pathways by which diverse carbohydrates are funneled into glycolysis including other monosaccharides, disaccharides, and polysaccharides like starch or glycogen.

Suggested Assignments

The question server contains a large, general section that covers a number of topics from metabolism including glycolysis, the citric acid cycle, and oxidative phosphorylation. After warming up with the terminology complete the crossword puzzle for energy metabolism. Here is the solution to the puzzle.

Read pp. 67-72 in ExamKrackers Biology I. Perform practice items 49-56 on pg. 76 (material also here from fatty acid and protein metabolism).

Review the web resources for glycolysis.

Conceptual Vocabulary for Glycolysis & Pyruvate Dehydrogenase

Glycolysis & Pyruvate Dehydrogenase

Each list begins with basic conceptual vocabulary you need to know for MCAT questions and proceeds to advanced terms that might appear in context in MCAT passages. The terms are links to Wikipedia articles.
Anaerobic organism
An anaerobic organism is any organism that does not require oxygen for growth.
Adenosine triphosphate
Adenosine triphosphate is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer.
Glycolysis is the initial process of most carbohydrate catabolism serving the functions of producing ATP and NADH, pyruvate for the citric acid cycle, and a variety of other compounds which are important for biosynthesis.
Pyruvic acid
Pyruvic acid is an alpha-keto acid which plays an important role in biochemical processes. It is an output of glycolysis.
Glucose 6-phosphate (also known as Robison ester) is glucose sugar phosphorylated on carbon 6.
Fermentation is respiration under anaerobic conditions with no external electron acceptor.
Ethanol fermentation
Ethanol fermentation is the biological process by which sugars such as glucose, fructose, and sucrose, are converted into ethanol and carbon dioxide.
A kinase, alternatively known as a phosphotransferase, is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific target molecules.
Phosphorylation is the addition of a phosphate group to a protein molecule or a small molecule.
Fructose 2,6-bisphosphate
Fructose 2,6-bisphosphate, is a metabolite that allosterically affects the activity of the enzymes phosphofructokinase 1 and fructose 1,6-bisphosphatase to regulate glycolysis and gluconeogenesis.
Futile cycle
A futile cycle is when two metabolic pathways run simultaneously in opposite directions and have no overall effect other than wasting energy.
Fructose 6-phosphate
Fructose 6-phosphate (also known as the Neuberg ester) is fructose sugar phosphorylated on carbon 6. The beta-D-form of this compound is very common in cells.
L-lactate is constantly produced in animals from pyruvate in a process of fermentation during normal metabolism and exercise.
Lactic acid fermentation
Lactic acid fermentation is a form of anaerobic respiration that occurs in some bacteria and animal cells in the absence of oxygen.
Adenosine monophosphate
Adenosine monophosphate is an ester of phosphoric acid with the nucleoside adenosine. AMP consists of the phosphate group, the pentose sugar ribose, and the nucleobase adenine.
Substrate-level phosphorylation
Substrate-level phosphorylation is a type of chemical reaction that results in the formation of ATP by the direct transfer of a phosphate group to ADP from a reactive intermediate.
Pyruvate decarboxylation
The pyruvate decarboxylation reaction links the metabolic pathways glycolysis and the citric acid cycle.
In glycolysis and photosynthesis, 1,3-Bisphosphoglycerate (1,3BPG) is a transitional stage between glycerate 3-phosphate and glyceraldehyde 3-phosphate during the fixation or reduction, respectively, of carbon dioxide.
2-Phosphoglycerate (2PG) is a glyceric acid which serves as the substrate in the ninth step of glycolysis. It is catalyzed by enolase into phosphoenolpyruvate (PEP), the penultimate step in the conversion of glucose to pyruvate.
A hexokinase is an enzyme that phosphorylates a six-carbon sugar, a hexose, to a hexose phosphate.
Enolase, or 2-phospho-D-glycerate hydrolyase, is an enzyme that participates in glycolysis, catalyzing the conversion of 2-phosphoglycerate to phosphoenolpyruvate, the penultimate step in the conversion of glucose to pyruvate.
Pyruvate kinase
Pyruvate kinase is an enzyme involved in glycolysis, catalyzing the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, yielding a pyruvate molecule and producing one molecule ATP.
Pyruvate dehydrogenase complex
Pyruvate dehydrogenase complex (PDC) is a complex of three enzymes that transform pyruvate into acetyl-CoA.
Entner-Doudoroff Pathway
The Entner-Doudoroff pathway in some prokaryotes describes a series of reactions that catabolize glucose to pyruvate using a different set of enzymes from those used in either glycolysis or the pentose phosphate pathway.
Aldolase A
Aldolase A is an enzyme which catalyses one of the aldol reactions of glycolysis in which fructose 1,6-bisphosphate is broken down into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
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