Question

What is true about the end products of glycolyss? (a) 2 pyruvic acid \(+2 \mathrm{ATP}+2 \mathrm{NADH}_{2}\) (b) 2 pyruvic acid \(+2 \mathrm{NADH}_{2}\) (c) 1 pyruvic acid \(+2 \mathrm{ATP}+2 \mathrm{NADH}_{2}\) (d) 2 pyruvic acid \(+1 \mathrm{ATP}+1 \mathrm{NADH}_{2}\)

Short answer

The correct end products of glycolysis are 2 pyruvic acid, 2 ATP, and 2 NADH, which corresponds to option (a).

Step-by-step solution

- Recall the Glycolysis Pathway

Review the glycolysis pathway to remember what it produces. Glycolysis is a metabolic process that breaks down glucose into pyruvate. The net end products of glycolysis from one molecule of glucose are: 2 pyruvic acid molecules, a net gain of 2 ATPs (4 ATP are produced but 2 are used), and 2 NADH molecules.

- Evaluate the Options

Compare the end products of glycolysis with the given options. The correct option should match the products mentioned in Step 1.

- Identify the Correct Answer

Option (a) 2 pyruvic acid + 2 ATP + 2 NADH is correct because it lists all end products of glycolysis accurately. ATP reflects net gains, which means the 2 ATP mentioned takes into account the initial investment of 2 ATP. Also note that the NADH produced is not NADH2, which is a common misconception. The correct term is NADH.

Key concepts

Glycolysis Pathway

The glycolysis pathway is a crucial biochemical sequence where glucose, a six-carbon sugar, is split and eventually converted into pyruvate, a three-carbon compound. This sequence occurs in the cytoplasm of cells and serves as the foundation for cellular respiration in both aerobic and anaerobic conditions.

During glycolysis, glucose undergoes a series of transformations. It's first 'activated' by the addition of two phosphate groups, which come from the consumption of two ATP molecules, turning glucose into fructose-1,6-bisphosphate. This step is critical because it traps the glucose in the cell and makes it more chemically reactive. After several steps, the fructose-1,6-bisphosphate is split into two three-carbon molecules, which are further processed to produce pyruvate.

Throughout this process, several key enzymes facilitate the reactions, ensuring glycolysis proceeds smoothly. One of these enzymes is hexokinase, which catalyzes the first step, while others like phosphofructokinase and pyruvate kinase catalyze later, vital stages. Understanding the roles of these enzymes can greatly improve the comprehension of how glycolysis is regulated and its pace determined.

ATP Production in Glycolysis

ATP production is a primary goal of glycolysis, and the pathway is carefully tuned to maximize energy extraction from glucose. Two ATP molecules are initially used to energize the glucose molecule, which may seem like an energy loss. However, this investment pays off later in the pathway.

As the three-carbon molecules are further processed, a total of four ATP molecules are produced through substrate-level phosphorylation. This means that during glycolysis, enzymes directly transfer phosphate groups to ADP, forming ATP. Two molecules are used up in the initial stages, which leaves the cell with a net gain of two ATP molecules per glucose molecule metabolized.

This net gain may seem modest, but the efficiency of glycolysis lies in its speed and ability to provide a quick supply of ATP, particularly important when cells require immediate energy, for example, during short bursts of intensive activity. The ATP produced can be utilized by the cell for various functions, from muscle contractions to active transport processes across membranes.

Glycolysis Net Gain

When considering the net gain from glycolysis, it is essential to account for all molecules consumed and produced. The process starts with one molecule of glucose and ultimately yields two molecules of pyruvate, along with a series of energy transfers and conversions.

The net gain from glycolysis, from each glucose molecule, is two ATP molecules and two NADH molecules. The ATP reflects the difference between the four ATP molecules generated and the two ATP molecules consumed during the initial reactions. The NADH molecules carry high-energy electrons to be later used in the electron transport chain during aerobic respiration, contributing to further ATP synthesis.

It's vital to understand that glycolysis doesn't just end with the production of pyruvate; it sets the stage for other metabolic pathways. The fate of pyruvate depends on oxygen availability. In the presence of oxygen, pyruvate enters the mitochondria and is further broken down in the citric acid cycle. In contrast, under anaerobic conditions, pyruvate may be converted into lactate in animal cells or ethanol and carbon dioxide in yeast, with no further ATP production.