Pyruvate: Formula, Synthesis, Oxidation, Carboxylation: Definition, Structure & Uses

What Is Pyruvate?

Pyruvate is regarded as one of the vital intermediates in quite several metabolic pathways. It is the end product of glycolysis, hence a critical element in cellular respiration. Pyruvate enters the cycle that occurs in glycolysis with the cycle of citric acid and oxidative phosphorylation.

Role in Glycolysis and Cellular Respiration

• The glycolysis pathway changes one glucose into two pyruvates, generating two ATP molecules and two NADH molecules.

• Pyruvate bears importance for cell respiration because it can further be metabolised for energy formation.

Relation to Metabolism

• Pyruvate is a metabolic crossroad that can link carbohydrate, fat, and protein metabolic processes.

• It can be converted into acetyl-CoA for the citric acid cycle or into lactic acid during anaerobic respiration.

Pyruvate vs Pyruvic Acid

Pyruvic acid is the form of the pyruvate in which it is in a protonated state (having added an H⁺).

Chemical Structure & Formula

Chemical Structure and Molecular Formula:

• Molecular formula: C₃H₄O₃

• Chemical structure: CH₃COCOOH, (pyruvic acid), CH₃COCOO⁻(pyruvate)

Physical Properties

• State: Solid at room temperature

• Colour: Colorless to white

• Melting Point: 165°C (329°F)

• Solubility: Soluble in Water

Synthesis of Pyruvate (Glycolysis End Product)

The synthesis of pyruvate involves:

Steps Leading to Pyruvate Formation

• Conversion to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

• Oxidation and phosphorylation to 1,3-bisphosphoglycerate.

• Conversion to 3-phosphoglycerate, 2–2-phosphoglycerate and then phosphoenolpyruvate.

• Final conversion to pyruvate.

Enzymes Involved

• Hexokinase

• Phosphofructokinase

• Pyruvate kinase

Energy Yield

• 2 molecules of ATP (net gain) per molecule of glucose

• 2 NADH molecules

Pyruvate as a Metabolic Crossroad

The details are given below:

Link Reaction (Conversion to Acetyl-CoA)

• Pyruvate is decarboxylated and attached to CoA to produce acetyl-CoA.

• It gives NADH and CO₂.

Enzyme Complex: Pyruvate Dehydrogenase

• A multi-enzyme complex made up of E1 (pyruvate dehydrogenase), E2 (dihydrolipoyl transacetylase), and E3 (dihydrolipoyl dehydrogenase).

• It helps to convert pyruvate to acetyl-CoA.

• Important in replenishing citric acid cycle intermediates (anaplerotic reactions) and gluconeogenesis.

Fate of Pyruvate (Aerobic vs Anaerobic)

The metabolic fate of pyruvate after glycolysis is:

Aerobic Pathway — Pyruvate Oxidation

In the presence of sufficient oxygen, pyruvate is transported into the mitochondria and then converted to acetyl-CoA by the pyruvate dehydrogenase complex. The produced acetyl-CoA will enter the citric acid cycle (Krebs cycle), where it becomes further oxidized into ATP, NADH, and FADH2 required for the electron transport chain.

Anaerobic Pathway — Reduction Reactions

In the absence of, or when oxygen is limited, the cells resort back to anaerobic pathways for energy generation.

• In lactic acid fermentation, when the amount of oxygen is inadequate during exercise or when oxygen demand is high, pyruvate is converted to lactate.

• Alcoholic fermentation in yeast and some bacteria, pyruvate is converted to ethanol and carbon dioxide through alcoholic fermentation.

Pyruvate Carboxylation

• Biotin-dependent enzyme.

• Catalyses the carboxylation of pyruvate to oxaloacetate.

Importance

• Gluconeogenesis: synthesis of glucose from noncarbohydrate sources

• Anaplerotic reactions: replenishing citric acid cycle intermediates

Regulation of Pyruvate Metabolism

The pyruvate metabolism is regulated by:

Allosteric Regulation

• Activator is fructose-1,6-bisphosphate

• Inhibitors is ATP, acetyl-CoA, NADH

Hormonal Regulation

• Insulin stimulates glycolysis.

• Glucagon stimulates gluconeogenesis.

Feedback Mechanisms

• High levels of ATP inhibit glycolytic enzymes.

• High levels of ADP activate glycolytic enzymes.

ATP Yield From Pyruvate Pathways

The details are given below:

Glycolysis

• Net gain of 2 ATP molecules per glucose molecule.

• 2 NADH molecules per glucose molecule.

Citric Acid Cycle

• Each acetyl-CoA produces 3 NADH, 1 FADH₂, and 1 GTP (equivalent to ATP).

• Total ATP yield from the complete oxidation of one glucose molecule: 30 - 32 ATP.

Pyruvate NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Chemical formula of pyruvate

• Regulation of Pyruvate metabolism

• ATP yield from pyruvate

Practice Questions for NEET

Q1. In anaerobic respiration, pyruvic acid undergoes

1. Krebs cycle

2. Electron Transport Chain

3. Fermentation

4. Both a and b

Correct answer: 3) Fermentation

Explanation:

There are three major ways in which different cells handle pyruvic acid produced by glycolysis:

• Lactic acid fermentation:- Under specific anaerobic conditions, particularly within animal muscle cells and certain bacterial species, pyruvic acid undergoes reduction to lactic acid facilitated by the enzyme lactate dehydrogenase, concurrently resulting in the oxidation of NADH to NAD+

• Alcoholic fermentation:- In species such as yeast and various bacteria, the process of decarboxylation transforms pyruvic acid into acetaldehyde which results in ethanol eventually.

• Aerobic respiration:- a cellular process in which glucose is completely oxidized to produce energy in the presence of oxygen.

Hence, the correct answer is option 3) Fermentation.

Q2. The key product of glycolysis is

1. Acteyl CoA

2. Phosphoenolpyruvate

3. Pyruvate

4. Carbon dioxide

Correct answer: 3) Pyruvate

Explanation:

The main byproduct of glycolysis is pyruvic acid. The pyruvate's metabolic requirement is contingent upon the cell's metabolic requirements. There are three major ways in which different cells handle pyruvic acid produced by glycolysis:

• Lactic acid fermentation

• Alcoholic fermentation

• Aerobic respiration

Hence, the correct answer is an option 3) The key product of glycolysis is pyruvate.

Q3. After glycolysis, pyruvate can be converted into which of the following?

1. Acetyl CoA

2. Lactate

3. Ethanol

4. All of the above

Correct answer: 4) All of the above

Explanation:

In the absence of oxygen, pyruvate cannot enter the aerobic Krebs cycle, so it undergoes fermentation to generate ATP. In animal cells, pyruvate is converted into lactate by lactate dehydrogenase, while in yeast and some bacteria, pyruvate is converted into ethanol by the enzyme pyruvate decarboxylase. Alternatively, pyruvate can be converted into acetyl-CoA by the enzyme pyruvate dehydrogenase, which then enters the Krebs cycle for further ATP production.

Hence, the correct option is 4) All of the above.

Also Read:

• MCQs on Metabolic Fate of Pyruvate

• TCA Cycle

• Entner Doudoroff Pathway

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