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Glycolysis or Embden-Meyerhof pathway is a set of biochemical reactions in which one mole of glucose molecule is broken down into two molecules of pyruvate. The process of glycolysis plays an important role in cellular respiration and generation of ATP both aerobically and anaerobically.
What is Glycolysis Pathway?
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The process of splitting of six-carbon molecule, glucose into two three carbon molecules of pyruvate which occurs in the cytoplasm of living organisms is called glycolysis. It is a multistep process which is catalyzed by set of enzymes.
- It is an oxygen independent process which can ever occur in absence of oxygen.
- The process of glycolysis is very significant in the generation of energy in the form of ATP.
- The steps of glycolysis is broadly categorized into two types: Preparatory and Payoff Phases.
Preparatory Phase
Preparatory phase includes the first five steps of glycolysis in which glucose molecule is phosphorylated into glyceraldehyde-3-phosphate along with the release of two adeno-tri-phosphate (ATP) molecules.
Payoff Phase
Payoff phase is the second phase of glycolysis pathway which involves the conversion of glyceraldehyde-3-phosphate into the final product called as pyruvate molecule.
Glycolysis Cycle
Glycolysis Steps
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The glycolysis pathway includes ten important steps:
Step1
The enzyme hexokinase adds a phosphate group to glucose in the cell's cytoplasm. In this step, a phosphate group is transferred from ATP to glucose, resulting in glucose,6-phosphate.
Step 2
The enzyme phosphoglucomutase converts glucose-6-phosphate into fructose-6-phosphate.
Step 3
The other ATP molecule attaches a phosphate group to fructose 6-phosphate, which is then converted into fructose 1,6-bisphosphate by the enzyme phosphofructokinase.
Step 4
The enzyme aldolase transforms fructose 1,6-bisphosphate to glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, which are isomers of one another.
Step 5
Triose-phosphate isomerase transforms dihydroxyacetone phosphate to glyceraldehyde 3-phosphate, which is the substrate in the next stage of glycolysis.
Step 6
This stage involves two reactions:
- The enzyme glyceraldehyde 3-phosphate dehydrogenase converts one hydrogen molecule from glyceraldehyde phosphate to nicotinamide adenine dinucleotide, resulting in NADH + H+.
- Glyceraldehyde 3-phosphate dehydrogenase adds phosphate to oxidized glyceraldehyde phosphate to produce 1,3-bisphosphoglycerate.
Step 7
Phosphate is transported from 1,3-bisphosphoglycerate to ADP by phosphoglycerokinase, which then converts to ATP. This process yields two molecules of phosphoglycerate and ATP.
Step 8
The enzyme phosphoglyceromutase relocates the phosphate of both phosphoglycerate molecules from the third to the second carbon, resulting in two molecules of 2-phosphoglycerate.
Step 9
The enzyme enolase converts 2-phosphoglycerate into phosphoenolpyruvate by removing a water molecule.
Step 10
The action of pyruvate kinase transfers a phosphate from phosphoenolpyruvate to ADP, resulting in pyruvate and ATP. The final products are two molecules of pyruvate and ATP.
Glycolysis Pathway
Regulation of Glycolysis Reactions
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Hexokinase, phosphofructokinase, and pyruvate kinase are three important enzymatic control points which regulates the irreversible steps of glycolysis.
- The conversion of glucose into glucose-6-phosphate is catalyzed by the action of hexokinase enzyme.
- The site of action of hexokinase and glucokinase enzymes in our body are liver and pancreas.
- The third step of glycolysis pathway which involves the conversion of fructose into fructose-1,6-biphosphase is mediated by phosphofructokinase enzyme.
- The last step, involving the synthesis of pyruvate molecule, final product of glycolysis is regulated by pyruvate kinase enzyme.
Significance of Glycolysis
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The following are the significance of Glycolysis
- This process is used by all cells and tissues to get energy, which is stored as ATP and NADH.
- It occurs in both prokaryotes and eukaryotes.
- It is used for both aerobic and anaerobic respiration.
- Glycolysis occurs in the cytoplasm, making it a significant source of energy for species that lack mitochondria.
- The end product of glycolysis is pyruvate, which acts as an intermediary in a variety of other processes like gluconeogenesis, fatty acid production, fermentation, and so on.
- Even glycolysis intermediates are used in other metabolic pathways; for example, DHAP (dihydroxyacetone phosphate) is reduced to glycerol 3-phosphate, which is then used to produce triglycerides.
- Glycolysis interacts with other processes such as lactate and ethanol fermentation, transamination to produce alanine, the pentose phosphate pathway, glycogen metabolism, and so on.
- When muscles require a lot of energy and there isn't enough oxygen, the anaerobic glycolysis pathway is used to create it.
- Erythrocytes, which lack mitochondria, obtain their energy from lactic acid fermentation.
- The lens of the eye is another example of anaerobic glycolysis.
- Because most reactions are reversible, gluconeogenesis converts pyruvate back into glucose.
Things to Remember
- The word glycolysis comes from the Greek terms glycos, which means sugar, and lysis, which means splitting.
- Gustav Embden, Otto Meyerhof, and J. Parnas devised the glycolysis scheme, which is known as the EMP pathway.
- Glycolysis is the partial oxidation of glucose, which is obtained from sucrose, to produce two molecules of pyruvic acid.
- Phosphoglucoisomerase isomerizes glucose-6-phosphate to create fructose-6-phosphate.
- The enzyme triose phosphate isomerase breaks down fructose 1, 6-diphosphate into dihydroxyacetone phosphate and 3-phosphoglyceraldehyde (PGAL).
- Glyceraldehyde 3-phosphate dehydrogenase is an enzyme that transforms 3-phosphate glyceraldehyde to 1,3-bisphosphoglycerate.
- 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase.
Sample Questions
Ques. What is the most crucial phase in the glycolysis process? (2 Marks)
Ans. The phosphofructokinase reaction is the most crucial regulatory step in glycolysis. The energy charge of the cell—that is, the proportion of the cell's adenosine nucleotides that contain high-energy bonds—controls phosphofructokinase.
Ques. In glycolysis, which ion is most important? (2 Marks)
Ans. Magnesium appears to be a major coherent controller of glycolysis and the Krebs cycle, according to previous research, including our computer simulation of cardiac energy metabolism. Mg2+ sensitivity affects many glycolytic enzymes.
Ques. In the final phase of glycolysis, which substrate is used? (2 Marks)
Ans. The final stage in glycolysis is completed by the enzyme pyruvate kinase (called after the reverse process of pyruvate conversion to PEP) and culminates in the creation of a second ATP molecule and the chemical pyruvic acid through substrate-level phosphorylation (or its salt form, pyruvate).
Ques. What is glycolysis' primary function? (2 Marks)
Ans. Glycolysis is the first of the primary metabolic processes in cellular respiration that produces energy in the form of ATP. Through a series of enzyme processes, the six-carbon ring of glucose is broken into two three-carbon sugars of pyruvate in two different phases.
Ques. What happens throughout the glycolysis process? (2 Marks)
Ans. The term "glycolysis" refers to the process of breaking glucose, which is exactly what happens at this stage. A molecule of glucose is divided into two molecules of pyruvate (also known as pyruvic acid) by enzymes. Glucose (C6) is divided into two 3-carbon (C3) pyruvate molecules during glycolysis. This causes energy to be released, which is then transferred to ATP.
Ques. Where does Glycolysis take place? What are the major enzymes involved in the process? (3 Marks)
Ans. The cytoplasm is where glycolysis takes place. The citric acid cycle takes place in the mitochondrial matrix, and oxidative metabolism takes place at the internally folded mitochondrial membranes (cristae).
Hexokinase, phosphofructokinase, and pyruvate kinase are the three major enzymes in glycolysis. Lactate dehydrogenase is a protein that catalyzes the conversion of pyruvate to lactate.
Ques. What are the fates of Pyruvate and NADH in glycolysis pathway? (3 Marks)
Ans. Two ATP, two NADH, and two pyruvate molecules are produced at the end of glycolysis. In cellular respiration, pyruvate can be broken down (oxidized) all the way to carbon dioxide if oxygen is present, resulting in numerous molecules of ATP. As part of a specific reaction, glycolysis requires NAD+ to receive electrons. This reaction can't proceed if there's no NAD+ around (since it's all stuck in its NADH), and glycolysis will stop. To keep glycolysis continuing, all cells need a method to convert NADH back to NAD+.
- There are two fundamental methods for doing so. NADH can send its electrons into the electron transport chain when oxygen is available, regenerating NAD+ for use in glycolysis.
- Cells may employ alternative, simpler methods to replenish NAD+ when oxygen is unavailable. NADH provides its electrons to an acceptor molecule in these routes, which does not produce ATP but does regenerate NAD+, allowing glycolysis to continue by a process called fermentation.
Ques. What is glycolysis known for? (2 Marks)
Ans. Glycolysis is a fundamental metabolic mechanism in which all cells oxidize glucose to produce energy in the form of ATP (adenosine triphosphate) and intermediates for use in other metabolic pathways.
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