Question

Write the overall equation for the conversion of pyruvate to acetyl CoA.

Short answer

Pyruvate + CoA + NAD⁺ → Acetyl CoA + NADH + CO₂.

Step-by-step solution

Identify the reactants

Determine the molecules involved before the conversion starts. Pyruvate (C₃H₄O₃), NAD⁺ (nicotinamide adenine dinucleotide), and Coenzyme A (CoA) are the initial reactants.

Identify the products

Identify the molecules formed after the conversion. Acetyl CoA (C₂H₃O-CoA), NADH (reduced NAD), and carbon dioxide (CO₂) are the products.

Write the conversion equation

Combine the reactants and products to form the balanced overall equation: Pyruvate + CoA + NAD⁺ → Acetyl CoA + NADH + CO₂.

Key concepts

Pyruvate

Pyruvate is a key intermediate in several metabolic pathways throughout the cell. This molecule is formed from glucose during glycolysis, which occurs in the cytoplasm of cells. Pyruvate consists of three carbon atoms, five hydrogen atoms, and three oxygen atoms, represented by the chemical formula C₃H₄O₃. During glycolysis, one molecule of glucose (a six-carbon compound) is broken down into two molecules of pyruvate. Pyruvate can then enter the mitochondria where it undergoes further processing.

Acetyl CoA

Acetyl CoA (Acetyl Coenzyme A) is a crucial molecule in metabolism, acting as a substrate for the citric acid cycle (Krebs cycle). This compound is formed from pyruvate through a process known as oxidative decarboxylation, which occurs in the mitochondria. The chemical formula for Acetyl CoA is C₂H₃O-CoA. It consists of an acetyl group (two carbon atoms, three hydrogen atoms, and one oxygen atom) linked to Coenzyme A (CoA). CoA is a coenzyme that helps in transferring the acetyl group to different molecules, facilitating various metabolic processes including energy production.

NAD⁺

NAD⁺ (Nicotinamide Adenine Dinucleotide) is a crucial coenzyme in cellular metabolism, especially in redox reactions. It serves as an electron carrier, picking up electrons from one reaction and donating them to another. In its oxidized form, denoted as NAD⁺, it accepts electrons during glycolysis and the citric acid cycle. This acceptance of electrons is coupled with the reduction of NAD⁺ to NADH, a key step in the process of energy extraction from nutrients.

NADH

NADH is the reduced form of NAD⁺, where it has accepted two electrons and one proton. This coenzyme plays a vital role in cellular respiration by carrying electrons to the electron transport chain, where they are used to generate ATP, the cell's energy currency. NADH is produced during glycolysis, the conversion of pyruvate to acetyl CoA, and the citric acid cycle. It essentially acts as a temporary energy storage molecule, which will later on be utilized to drive ATP synthesis in the mitochondria.

Carbon Dioxide

Carbon dioxide (CO₂) is a simple gas that is produced as a byproduct during the conversion of pyruvate to acetyl CoA. This process is known as oxidative decarboxylation, where a carboxyl group is removed from pyruvate and released as CO₂. The formation of CO₂ is essential as it helps drive the conversion process and allows the cell to get rid of excess carbon atoms. CO₂ is then transported out of the cell and ultimately exhaled out of the body during respiration.

Biochemistry

Biochemistry is the study of chemical processes within and related to living organisms. It is a laboratory-based science that combines biology and chemistry, employing techniques of both to understand the molecular mechanisms which give rise to the complexity of life. Understanding biochemistry is crucial for comprehending how cells harness energy from nutrients, and how various biochemical pathways interconnect. The conversion of pyruvate to acetyl CoA is a prime example of a biochemical process that is fundamental to cellular respiration and energy production.