The mitochondrial inner membrane carries out the electron transport chain, an important step in releasing energy from simple food molecules within the cell. Learn about the membrane structures called cristae and how they enhance the membrane’s ability to function.
What Are Mitochondrial Cristae?
Mitochondrial cristae are folds of the mitochondrial inner membrane that provide an increase in the surface area. This allows a greater space for processes that happen across this membrane. The electron transport chain and chemiosmosis are the processes which help produce ATP in the final steps of cellular respiration.
The following picture is the mitochondrion, showing the inner membrane, including the cristae:
Function of Mitochondrial Cristae
Before we can explain the functioning of the crista (plural = cristae), we need to revisit what a mitochondrion does. The mitochondrion is the cellular organelle where cellular respiration takes place. Cellular respiration is the process that creates chemical energy in the form of ATP from simple food molecules.
These food molecules, particularly glucose, are first broken down in the cytosol outside the mitochondrion during glycolysis.After glycolysis, the remnants of the glucose molecules make it into the mitochondria. This begins aerobic cellular respiration. First, the citric acid cycle takes place in the mitochondrial matrix; this releases a few ATP and creates NADH and FADH2 electron carrier molecules that get passed along to the next stage, the electron transport chain.
The electron transport chain uses electrons from NADH and FADH2. These electrons are passed along by proteins embedded within the membrane and produce molecules of H2O. H+ ions (protons) from these carriers are shuttled ‘across’ the inner membrane and into the inter-membrane space between the inner and outer mitochondrial membranes.The buildup of H+ ions in the inter-membrane space creates a proton potential.
During chemiosmosis, the protons funnel through an ATP synthase protein in the inner membrane. As they do, the ATP synthase spins to create ATP from ADP and phosphate. Thus, the proton potential provides the energy for making ATP.Cristae are folds of the inner mitochondrial membrane. The electron transport chain and chemiosmosis takes place on this membrane as part of cellular respiration to create ATP and can be seen in the diagram:
The cristae increase the surface area of the inner membrane, allowing for faster production of ATP because there are more places to perform the process.
So, how do these folds increase surface area? Imagine a square membrane with a perimeter of 800 nanometers. Each side is 200 nm (billionths of a meter) long. If the height was 25 nm, there would be exactly 20,000 square nm of surface for the production of ATP. If the inner membrane of the mitochondrion were square, it would have a limited surface for ATP production.
In the following diagram, note the ATP synthase molecules allowing H+ ions to funnel through.
Now, if we increase the perimeter of that membrane by including a fold, we get more surface area without taking up more space. Let’s say the new fold adds another 200 nm to the perimeter, at the same height of 25 nm.
This increases the surface area by 5,000 square nm, to a total of 25,000. The crista is the fold that allows for the embedding of more ATP synthase molecules in the membrane, and therefore, more ATP production at the same time.
Let’s review. Mitochondrial cristae are folds of the mitochondrial inner membrane that provide an increase in the surface area.
Having more cristae gives the mitochondrion more locations for ATP production to occur. In fact, without them, the mitochondrion would not be able to keep up with the cell’s ATP needs.This concept of greater surface area also works in other parts of the human body. For example, the lining of the intestine has structures called villi that increase the surface area for the absorption of nutrients.
Vocabulary & Definitions
Mitochondrial cristae are folds of the mitochondrial inner membrane that provide an increase in the surface area.Electron transport chain: The electron transport chain helps to produce ATP.Chemiosmosis: Chemiosmosis is the process that helps produce ATP in the final steps of cellular respiration.Mitochondrion: Mitochondrion is the cellular organelle in which cellular respiration takes place.Cellular respiration: Cellular respiration is the process that creates chemical energy in the form of ATP from simple food molecules.Glycolysis: Glycolysis is the process by which glucose is first broken down.
Explore these facts about mitochondrial cristae, then do the following to test your understanding:
- Define mitochondrial cristae
- Explain the function of mitochondrial cristae