Cellular Respiration: How Cells Make Energy

The notes in this series on cellular microbiology are all created using ChatGpt. So do cross check and verify on your own too

Cellular respiration is the process by which cells convert glucose (a type of sugar) into energy in the form of ATP. Think of it as the way cells “breathe” and get fuel to do all their work.

Where Does Cellular Respiration Happen?

In animal cells: This process mainly happens in the mitochondria, the “power plants” of the cell.

In plant cells: It happens in the mitochondria as well (even though plants can also make their own food using photosynthesis).

The Steps of Cellular Respiration

Cellular respiration happens in a few key stages, each one breaking down glucose a little more:

1. Glycolysis – Breaking Down Glucose (In the Cytoplasm)

Where: This happens in the cytoplasm of the cell.

What happens: Glucose (a 6-carbon sugar) is broken down into two molecules of pyruvate (each with 3 carbons).

Energy produced: A small amount of ATP (2 ATP molecules).

Byproducts: Also, some electrons are captured on carriers called NADH.

2. The Citric Acid Cycle (Krebs Cycle) – Generating Electron Carriers (In the Mitochondria)

Where: This happens inside the mitochondria.

What happens: The pyruvate from glycolysis is broken down further in the citric acid cycle.

Energy produced: A small amount of ATP (2 ATP molecules).

Byproducts: Lots of NADH and FADH₂ (electron carriers) are produced, as well as CO₂ (carbon dioxide), which the cell releases as waste.

3. Electron Transport Chain – The Big Energy Generator (In the Mitochondria)

Where: This takes place in the inner membrane of the mitochondria.

What happens: The NADH and FADH₂ molecules (from the previous steps) donate electrons to the electron transport chain. These electrons move through a series of proteins, creating a proton gradient (like a dam holding water).

Energy produced: This process generates the bulk of the cell’s ATP—around 32-34 ATP molecules per glucose molecule!

Byproducts: At the end of the chain, oxygen (O₂) combines with electrons and protons to form water (H₂O), which is released as a waste product.

Key Points to Remember

1. Oxygen is essential: Cellular respiration needs oxygen to work efficiently. This is why aerobic respiration (with oxygen) generates much more ATP than anaerobic respiration (without oxygen).

2. Glucose and oxygen: Glucose provides the fuel, while oxygen acts as the final electron acceptor to help generate lots of energy.

3. ATP is the goal: ATP is the “energy currency” of the cell, and cellular respiration is how cells make most of it.

Summary of Cellular Respiration

1. Glycolysis: Breaks down glucose into pyruvate, producing 2 ATP.

2. Citric Acid Cycle: Further breaks down pyruvate, producing electron carriers and 2 ATP.

3. Electron Transport Chain: Uses those electrons to create a proton gradient and produces 32-34 ATP.

In total, cellular respiration can produce up to 36-38 ATP molecules from a single glucose molecule!

Anaerobic Respiration (Without Oxygen)

When oxygen isn’t available, some cells (like yeast or muscle cells during intense exercise) switch to anaerobic respiration or fermentation.

What happens: Only glycolysis can occur, which produces 2 ATP.

Byproducts: Instead of CO₂ and water, anaerobic respiration produces lactic acid (in animals) or alcohol (in yeast).

This process is the foundation of how living organisms, from yeast to humans, generate the energy they need to survive and function!