Question

Describe in general terms the structural makeup of a mitochondrion.

Short answer

A mitochondrion has an outer membrane, an inner membrane folded into cristae, an intermembrane space, and a matrix containing DNA and ribosomes.

Step-by-step solution

Understand the Overall Structure

Mitochondria are double-membraned organelles within eukaryotic cells. They are known for their bean-like shape, but can also appear in various forms such as round or rod-shaped structures.

Explore the Outer Membrane

The outer membrane of a mitochondrion is a smooth, protective barrier that encloses the organelle. It contains proteins known as porins that allow the passage of ions and small molecules.

Investigate the Inner Membrane

The inner membrane is highly folded into structures called cristae, which increase the surface area of the membrane. This membrane is impermeable to most ions and small molecules, allowing the mitochondrion to maintain an internal environment distinct from the cytosol.

Examine the Intermembrane Space

Located between the outer and inner membranes, the intermembrane space acts as a reservoir for protons (H+ ions) that are involved in the chemiosmotic process of ATP production.

Look Inside the Matrix

The innermost compartment of the mitochondrion is the mitochondrial matrix. It contains enzymes responsible for the citric acid cycle and has mitochondrial DNA and ribosomes.

Key concepts

Double-Membrane Organelles

Mitochondria are fascinating structures within eukaryotic cells that feature a unique double-membrane design. This means they have two distinct layers of membrane that surround them. The outer membrane serves as a protective coat, helping to shield the inner components from external harm and maintaining the shape of the organelle, which can range from bean-shaped to round or rod-like forms.

The outer membrane is smooth and houses proteins called porins, which form channels through which ions and small molecules can pass. This feature allows the mitochondria to exchange essential materials with the cell's cytosol. Inside the outer membrane is the inner membrane, which is highly involved in the mitochondria’s primary function: energy production.

• Outer membrane: Smooth and permeable to small molecules and ions.
• Inner membrane: Contains folds called cristae, vital for its functions.

Cristae

Cristae are the intricate folds of the inner membrane of mitochondria, and they play a crucial role in the energy-making process. These folds increase the surface area of the inner membrane significantly, allowing for a larger number of electron transport chains. The chains are essential for the mitochondria's function of generating ATP, the energy currency of the cell.

These folds are not just there for structural complexity; they serve to optimize the space available for biochemical reactions that produce energy. The larger surface area means more space for reactions to take place, which boosts the efficiency of ATP production. Furthermore, the unique structure of the cristae allows for the compartmentalization of processes within the mitochondrion, maintaining distinct environments necessary for different stages of energy production.

Mitochondrial Matrix

Deep within the mitochondrion, past the inner membrane and cristae, lies the mitochondrial matrix. This central compartment is a hub of metabolic activity. Here, you will find various enzymes that are key players in the citric acid cycle, also known as the Krebs cycle.

The matrix is like a small biochemical laboratory. It contains a mix of substrates, intermediates, and enzymes necessary for energy production. In addition to enzymes, the matrix also houses mitochondrial DNA and ribosomes, enabling the mitochondria to produce some of its own proteins independently. The presence of DNA and ribosomes highlights the semi-autonomous nature of mitochondria within cells.

• Citric acid cycle enzymes: Central to energy conversion processes.
• Contains its own genetic material and protein synthesis machinery.

ATP Production

ATP production is the primary function of mitochondria, and it occurs through a process known as oxidative phosphorylation. This process takes place on the inner membrane's cristae, where oxygen and nutrients are converted into ATP. It involves a series of reactions, primarily driven by electron transport chains located on the cristae.

During this process, electrons are transferred through various complexes, which release energy. This energy is used to pump protons into the intermembrane space, creating a proton gradient. The flow of these protons back into the mitochondrial matrix through ATP synthase synthesizes ATP from ADP and inorganic phosphate. This is the vital energy currency used by the cell for various functions.

• Electron transport chains: Key to the ATP-making process.
• ATP synthase: The enzyme that generates ATP.

Eukaryotic Cells

Eukaryotic cells are complex, compartmentalized cells that contain membrane-bound organelles, including mitochondria. Unlike prokaryotic cells, eukaryotic cells have a nucleus that houses their DNA, as well as various organelles that perform specialized functions. Within eukaryotic cells, mitochondria are the powerhouses responsible for producing the energy needed for cellular activities.

These cells make up all plants, animals, fungi, and protists. The presence of mitochondria and other organelles allows eukaryotic cells to perform complex functions, manage biochemical pathways, and reproduce efficiently. This compartmentalization enables different processes to occur simultaneously in separate locations within the cell.

• Nucleus: Contains the cell's genetic material.
• Organelles: Specialized structures that perform unique roles.
• Eukaryotic organisms: Include animal and plant cells, among others.