Cellular Respiration: Formula, Definition, and Function

October 6, 2023

One of the great pleasures in life is enjoying a delicious, sweet treat. All the treats that we enjoy during the fall from Halloween to Thanksgiving or during the spring from Valentine’s Day to Easter give us a huge energy boost. Whatever the season, it is fitting to talk about how we transform candy and snacks into energy in our bodies with the cellular respiration formula.

 

ATP: The Energy Molecule

ATP or adenosine triphosphate is the molecule that our body uses to carry and use energy throughout the body. When you remove one of the phosphate groups from the molecule, there is an exchange of energy that can be used to do work such as muscle contraction or the movement of materials in and out of the cell. Energy is essential for life, but based on the law of conservation of energy, energy can neither be created nor destroyed. Therefore, how do we get ATP? Where does it come from?

 

Cellular Respiration – How we get from Food to Fuel

Though we can use many molecules in our food, we mainly use glucose or sugar to generate ATP. Cellular Respiration is the name for the group of processes that allow us to get energy from glucose. Glucose is a high energy molecule and provides about 38 ATP after the entire cellular respiration process is complete. This means that glucose is a wonderful source of energy, and through a series of cycles can be transformed from sugar (C₆H₁₂O₆) to water (H₂O), carbon dioxide (CO₂) and energy in the form of ATP.  In this article we will mainly focus on glucose as our energy source, but do not forget that proteins and fats also provide us energy that is essential for our survival.

 

The overall chemical formula for cellular respiration is:

 

C₆H₁₂O₆ + 6O₂ -> 6CO₂ + 6H₂O + ATP

 

Cellular respiration contains three main processes, glycolysis, the tricarboxylic acid cycle (Kreb’s Cycle), and the electron transport chain. Without all three cycles, you are unable to generate the maximum amount of ATP, but for all of these to occur, you need to have oxygen. Most of the time in our ecosystem oxygen is abundant, therefore cellular respiration uses oxygen. This is called aerobic respiration. We will save the discussion on what happens when you do not have oxygen, or during anerobic respiration, for another article.

 

Breakdown of the Cellular Respiration Formula

Step 1: Glycolysis

 

Glycolysis is the first pathway in cellular respiration and is named for the fact that glucose is broken down into pyruvate during this step (glyco- = sugar, -lysis = break apart). This process both requires ATP and generates ATP, but only contributes to a fraction of the ATP produced during cellular respiration. Glycolysis produces only 2 net ATP of the 38 total produced during aerobic respiration. This pathway does not require oxygen and is a part of both anerobic and aerobic respiration. In addition, glycolysis produces NADH, which is the mechanism that is used to bring hydrogen ions to the 3^rd step: the Electron Transport Chain

 

Main Products of Glycolysis:

NADH
ATP
Pyruvate

 

Step 2: The Tricarboxylic Acid Cycle

The final product of glycolysis is pyruvate, and prior to step 2, has to be converted into acetyl-CoA. This begins the tricarboxylic acid cycle (TCA), which generates ATP, but more importantly, harvests high energy electrons from the remaining glucose skeleton to be brought to our 3^rd step: the Electron Transport Chain. The TCA cycle is complex, but this diagram is a simple representation of the main products of this cycle being NADH and FADH, which are our electron carriers, as well as ATP and CO₂.

 

Main Products of the TCA Cycle:

NADH
FADH2
ATP
CO2

 

Step 3: The Electron Transport Chain

Last but certainly not least, the Electron Transport Chain is the process where the electrons from the hydrogen atoms from the original glucose molecule are used to generate the vast majority of ATP. This is done via a process called oxidative phosphorylation, where the energy captured from the movement of hydrogen ions is used to add a phosphate group onADP or adenosine diphosphate to create ATP. This process generates water and uses the NADH and FADH from previous steps. Oxygen is essential in this step, and without it, we are unable to generate the majority of ATP from cellular respiration.

 

Main Products of the Electron Transport Chain:

ATP
H₂O

 

What happens when we run out of oxygen?

 

 

During an intense workout, your body might be performing cellular respiration at a higher rate than your breathing can keep up with. This causes your cells to undergo a process called anaerobic respiration. In addition to aerobic respiration, this processallows your body to generate some energy without oxygen. This only produces a few ATP per glucose in comparison to the 38 produced during aerobic respiration, and therefore you are unable to sustain your body for extended periods of time exclusively using anerobic respiration.

 

Though we often do not think about the complex processes that allow us to thrive, it is important that all of these steps are functional for us to be able to grow and move. There are over 100 steps in a complete diagram of cellular metabolism, including proteins, nucleic acids, and fats, all of which are critical in how we process and respond to foods every day!

 

 

 

 

 

 

 

 

 

Author: Sydni Britton