Bioenergetics on the MCAT

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Bioenergetics is the study of all energy made or lost through chemical bonds in living organisms. This guide will introduce bioenergetics, key terms, and definitions you should remember as you prepare for the MCAT

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Bioenergetics on the MCAT: What Do You Need to Know?

Bioenergetics is covered in the Biochemistry section of the MCAT.

Introductory biochemistry accounts for 25% of the Biological and Biochemical Foundations of Living Systems section (Bio/Biochem) and 25% of the Chemical and Physical Foundations of Biological Systems section (Chem/Phys).

It’s hard to predict the exact number of questions about bioenergetics that will appear on the MCAT. However, you can expect it to appear in both the Bio/Biochem and Chem/Phys sections.

Important Sub-Topics – Bioenergetics

We cannot stress enough the importance of bioenergetics during MCAT prep since it is relevant to general chemistry, another important MCAT topic! 

Bioenergetics can be complicated, so let’s break them down into important sub-topics you can concentrate on.

1. Bioenergetics: Thermodynamics of Biological Systems

The study of thermodynamics describes how energy within a system can change. Thermodynamics can be measured, and one example is through Gibbs free energy. Gibbs free energy is used to measure the maximum amount of work done in a thermodynamic system when the temperature and pressure are kept constant.

The change in Gibbs free energy (𝜟G) determines the spontaneity of a biochemical reaction and whether energy has been released or put into the system.

The Change In Gibbs Free Energy (𝜟G)


Free Energy

Negative 𝜟G



Positive 𝜟G



For more in-depth content review on thermodynamics of Biological systems, check out these detailed lesson notes created by top MCAT scorers. 

2. Bioenergetics: Adenosine Triphosphate (ATP)

Adenosine Triphosphate (ATP) is the cell’s main energy source. ATP is composed of a ribose sugar with an adenine base attached at the C1 carbon and 3 phosphate groups.

The release of one of these phosphate groups from the ATP molecule results in a considerable energy release. This is seen in both ATP hydrolysis and phosphoryl group transfers.

For more in-depth content review on adenosine triphosphate (ATP), check out these detailed lesson notes created by top MCAT scorers. 

3. Bioenergetics: Biological Oxidation-Reduction Reactions

A lot of biochemical processes involve the transfer of electrons! This transfer occurs through oxidation-reduction reactions.

Two half reactions exist: oxidation and reduction. In many biochemical reactions, the reduction half-reaction results in the production of high-energy electron carriers. 

These are used in many reactions but are most significant in the electron transport chain. Examples include molecules such as Nicotinamide Adenine Dinucleotide and Flavin Adenine Dinucleotide.

Bioenergetics Biological Oxidation-Reduction Reactions

For more in-depth content review on biological oxidation-reduction reactions, check out these detailed lesson notes created by top MCAT scorers. 

Key Terms and Definitions – Bioenergetics

Here are some of the more important key terms and definitions to remember for this general guide to bioenergetics!



Gibbs free energy

Measures the maximum amount of work done in a thermodynamic system when the temperature and pressure are kept constant.


Energy is released during the reaction


Energy is absorbed during the reaction


Results in the loss of electrons


Results in the gain of electrons

Additional FAQs – Bioenergetics on the MCAT

What is the difference between bioenergetics and thermodynamics?

Bioenergetics refers to energy flow, while thermodynamics focuses on heat and temperature. The two are related as heat and temperature can have an effect on energy, work, radiation, and properties of matter.

What is an example of bioenergetics in biochemistry?

Some examples of bioenergetic processes include – glycogenesis, gluconeogenesis, and the citric acid cycle.

What are the 3 bioenergetic systems?

Since we do not store a significant amount of ATP and need a continuous supply, it must be constantly resynthesized. We can achieve this through these energy systems – phosphagen, anaerobic, and aerobic.

Is thermodynamics a topic on the MCAT?

Thermodynamics is definitely an important topic on the MCAT. Thermodynamics is covered in introductory biochemistry which comprises 25% of the biology/biochemistry section and 25% of the chemistry/physics section. Due to introductory biochemistry being such a large part of both the bio/biochem and chem/phys sections, it would be a good idea to understand thermodynamics for the MCAT.

Additional Reading Links – Study Notes for Bioenergetics on the MCAT

For more in-depth content review about bioenergetics on the MCAT, check out these detailed lesson notes created by top MCAT scorers!

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