Why does mitochondria have two membranes

Mitochondria are small organelles floating free throughout the cell. Some cells have several thousand mitochondria while others have none. Muscle cells need a lot of energy so they have loads of mitochondria. If a cell feels it is not getting enough energy to survive, more mitochondria can be created. Sometimes a mitochondria can grow larger or combine with other mitochondria.

It all depends on the needs of the cell. Mitochondria Structure Mitochondria are shaped perfectly to maximize their productivity. They are made of two membranes. The outer membrane covers the organelle and contains it like a skin.

The inner membrane folds over many times and creates layered structures called cristae. The fluid contained in the mitochondria is called the matrix.

The folding of the inner membrane increases the surface area inside the organelle. When at this contact site, the receptor protein hands off the tethered protein to the translocator protein, which then channels the unfolded protein past both the inner and outer mitochondrial membranes. Figure Detail. Mitochondria cannot be made "from scratch" because they need both mitochondrial and nuclear gene products. These organelles replicate by dividing in two, using a process similar to the simple, asexual form of cell division employed by bacteria.

Video microscopy shows that mitochondria are incredibly dynamic. They are constantly dividing, fusing, and changing shape. Indeed, a single mitochondrion may contain multiple copies of its genome at any given time. This page appears in the following eBook. Aa Aa Aa. Mitochondria are unusual organelles. They act as the power plants of the cell, are surrounded by two membranes, and have their own genome. They also divide independently of the cell in which they reside, meaning mitochondrial replication is not coupled to cell division.

Some of these features are holdovers from the ancient ancestors of mitochondria, which were likely free-living prokaryotes. What Is the Origin of Mitochondria? Figure 1: A mitochondrion. What Is the Purpose of a Mitochondrial Membranes?

Figure 2: The electrochemical proton gradient and ATP synthase. At the inner mitochondrial membrane, a high energy electron is passed along an electron transport chain. Is the Mitochondrial Genome Still Functional? Figure 3: Protein import into a mitochondrion. A signal sequence at the tip of a protein blue recognizes a receptor protein pink on the outer mitochondrial membrane and sticks to it. Logically, mitochondria multiply when a the energy needs of a cell increase.

Therefore, power-hungry cells have more mitochondria than cells with lower energy needs. For example, repeatedly stimulating a muscle cell will spur the production of more mitochondria in that cell, to keep up with energy demand. Mitochondria, the so-called "powerhouses" of cells, are unusual organelles in that they are surrounded by a double membrane and retain their own small genome.

They also divide independently of the cell cycle by simple fission. Mitochondrial division is stimulated by energy demand, so cells with an increased need for energy contain greater numbers of these organelles than cells with lower energy needs. Topic rooms within Cell Biology Close. No topic rooms are there. Or Browse Visually. Student Voices. Creature Cast. The prokaryotes are believed to have relinquished certain genes to the nuclei of their host cells, a process known as endosymbiotic gene transfer.

For this reason, mitochondria and chloroplasts now depend on their hosts to synthesize most of their components. Source: Saunders College Publishing. Thus eukaryotic cells are a sort of genetic hybrid, assembled from parts of various organisms. This endosymbiosis, this founding partnership, is certainly one of the most important events in the history of evolution. But this endosymbiosis also has some negative implications for the host cell. While the mitochondria provide this cell with highly efficient energy production, in the same process they also produce waste materials, the infamous free radicals, which are highly toxic to such cells and are considered one of the main causes of ageing.

On the basis of the rate of mutation of mitochondrial DNA, we can estimate the number of years that separate human beings from a common ancestor. However, this estimate is still the subject of debate.