Cristae

Cristae Definition

Cristae are sub-compartments of the inner membrane of mitochondria and are essential to mitochondrial function. Mitochondria are often considered the powerhouses of the cell since they are the organelles responsible for the generation of ATP, the energy currency of the cell.

Mitochondria are comprised of an outer and an inner membrane. Each membrane has a distinct form and purpose. The outer membrane controls the organelle’s shape and is essential for the communication of mitochondria with other organelles. The inner mitochondrial membrane is made up of two sub-compartments: 1) the inner boundary membrane, which is adjacent to the outer membrane, and 2) the folded cristae whose protrusions and folds penetrate the inner mitochondrial matrix.

The folded cristae membrane contains cylindrical connections to the inner membrane called cristae junctions.

Types of Cristae

Cristae Membrane

The main function of mitochondria is the use of carbohydrates to generate ATP through oxidative phosphorylation. Cristae membranes and cristae junctions are an integral part of this process.

The folding or wrinkling of the cristae on the inner mitochondrial membrane creates a large surface area inside the mitochondria. The number of cristae in the mitochondria reflects the particular cell’s demand for ATP. For example, heart muscle cells contain up to three times more cristae than other cells due to the greater need for ATP. The cristae membrane is where the electron transport chain, and enzymes of oxidative phosphorylation such as ATP synthase and succinate dehydrogenase are located.

The electron transport chain creates an electrochemical gradient across the inner mitochondrial membrane. This gradient drives the production of ATP from ADP and inorganic phosphate by the mitochondrial F₁F_o-ATP synthase reaction. The F₀ part of the enzyme is rooted in the cristae, while the F₁ extends into the mitochondrial matrix.

The diagram below shows the electron transport chain, the machinery that makes ATP, located in the inner mitochondrial membrane:

Cristae Junctions

Cristae junctions are tubular structures measuring 12-40nm in diameter that demarcate the cristae from the rest of the inner boundary membrane. These junctions allow the selective concentration of enzymes such F₁F₀-ATP synthase on the cristae. Many enzymes involved in oxidative phosphorylation are selectively imported to the cristae and can be retained in this region of the mitochondrial membranes due to the presence of junctions. Additionally, the F₁F₀-ATP synthase is also involved in determining the structure of the cristae itself.

Cristae junctions are also important for inter-mitochondrial communication. Cristae of nearby mitochondria arrange themselves to be parallel to each other and perpendicular to the connections between mitochondria. This formation facilitates electrochemical coupling allowing the mitochondria to function in synchrony. Thus, cristae are important components of intercellular and intracellular mitochondrial networks as ions and molecules are exchanged across the cristae and in between membranes.

Examples of Cristae Disorders

Unusual inner membrane structures are observed in many human disorders and during programmed cell death. For example, in amyotrophic lateral sclerosis (ALS) disease, Alzheimer’s disease and Parkinson’s disease, cristae morphology is disrupted by inclusions within mitochondria, as well as irregular inner membrane configurations.

Related Biology Terms

• Electron transport train – Sometimes called respiratory chain, this refers to a series of proteins located on the inner mitochondrial membrane that receive high-energy electrons produced by the citric acid cycle. As the electrons move through multiple members of this chain, they gradually lose energy, which in turn, is used to generate a proton gradient across the inner mitochondrial membrane.
• F₁F_o-ATP synthase – The enzyme present on mitochondrial cristae responsible for the synthesis of adenosine triphosphate (ATP).
• Mitochondria – Eukaryotic organelles wrapped in a double membrane and found in the cell cytoplasm. Their main function is to participate in aerobic respiration and generate ATP.

Quiz

1. On which of these mitochondrial structures are cristae found?
A. The outer membrane
B. The inner membrane
C. The matrix
D. All of the above

2. Which statement is true about cristae?
A. The wrinkled form of cristae increases the surface area of the inner mitochondrial membrane.
B. Cristae are located inside the nucleus.
C. Cristae do not play a role in allowing mitochondria to communicate with other mitochondria in the cells.
D. Cristae are part of the plasma membrane.

3. Which of the following statements is true?
A. Cristae membrane surface area size is proportional to a cell’s capacity for ATP generation.
B. Cristae membranes are deformed in diseases such as Parkinson’s and Alzheimer’s.
C. The cylindrical connections between cristae membranes and the inner membrane boundary of mitochondria are called cristae junctions.
D. All of the above.