describe 4 steps of "Aerobic Cellular Respiration"
Aerobic cellular respiration is the process by which cells convert oxygen and glucose into energy, carbon dioxide, and water. It occurs in three main steps: glycolysis, the citric acid cycle (also known as the Krebs cycle), and the electron transport chain. Here are the four major steps involved in aerobic cellular respiration:
1. Glycolysis:
Glycolysis is the first step in aerobic cellular respiration, and it takes place in the cytoplasm of the cell. Here's how it works:
- Glucose (a six-carbon molecule) is broken down into two molecules of pyruvate (a three-carbon molecule).
- This process requires two molecules of ATP (adenosine triphosphate) to break down glucose and generates four molecules of ATP, resulting in a net gain of two ATP molecules.
- Moreover, two molecules of NAD+ (nicotinamide adenine dinucleotide) are reduced to form two molecules of NADH.
- At the end of glycolysis, a small amount of ATP is generated along with two molecules of pyruvate.
2. Pyruvate Decarboxylation:
The next step depends on whether oxygen is present or not. In the presence of oxygen, pyruvate molecules are transported into the mitochondria. Within the mitochondria, pyruvate is converted into Acetyl-CoA through a series of reactions. This step is known as pyruvate decarboxylation since it involves the removal of a carbon atom from pyruvate, which is released as carbon dioxide. This process generates two molecules of NADH per each pyruvate.
3. Citric Acid Cycle (Krebs Cycle):
The citric acid cycle takes place in the mitochondria. In this step, Acetyl-CoA enters a series of enzymatic reactions, resulting in the production of energy-rich molecules.
- Acetyl-CoA combines with a four-carbon molecule called oxaloacetate to form a six-carbon molecule called citric acid.
- Through a series of reactions, citric acid is broken down, regenerating oxaloacetate in the process.
- Throughout the cycle, three molecules of NADH, one molecule of ATP, one molecule of FADH2 (flavin adenine dinucleotide), and two molecules of carbon dioxide are produced per one cycle.
4. Electron Transport Chain:
The final step of aerobic respiration takes place in the inner mitochondrial membrane and is known as the electron transport chain (ETC). The ETC is a series of protein complexes that transport electrons extracted from NADH and FADH2 produced from the previous steps.
- As electrons move through the ETC, energy is released and used to pump protons (H+) from the mitochondrial matrix to the intermembrane space.
- This creates an electrochemical gradient, and as protons move back into the matrix through ATP synthase, ADP (adenosine diphosphate) is phosphorylated to produce ATP.
- The electrons are eventually transferred to an oxygen molecule, forming water.
- This step generates the majority of the ATP produced in aerobic respiration.
Overall, these four steps of aerobic cellular respiration work together to efficiently break down glucose and produce energy (ATP) for cellular function.