The similar in structure to ribosomes found in

The mitochondrion is one of the most important organelles in eukaryotic cells. Inside the double membranes of the mitochondrion is a matrix.

Discover the nature of the mitochondrial matrix and the processes that occur there.

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The Mitochondrial Matrix Defined

The mitochondrion consists of an outer membrane, an inner membrane, and a gel-like material called the matrix. This matrix is more viscous than the cell’s cytoplasm as it contains less water. The mitochondrial matrix has several functions.It is where the citric acid cycle takes place. This is an important step in cellular respiration, which produces energy molecules called ATP.

It contains the mitochondrial DNA in a structure called a nucleoid. A mitochondrion contains its own DNA and reproduces on its own schedule, apart from the host cell’s cell cycle. It contains ribosomes that produce proteins used by the mitochondrion. It contains granules of ions that appear to be involved in the ionic balance of the mitochondrion.This picture shows the mitochondrion.

Folds of the inner membrane are called cristae and this is where the matrix resides.

Function of the Mitochondrial Matrix

The mitochondrion is an organelle that performs the process of aerobic respiration. In aerobic respiration, simple food molecules like glucose are broken down for their energy. The process results in high-energy molecules called ATP.The citric acid cycle is the first stage of aerobic respiration.

It takes place in the mitochondrial matrix. The cycle is named for the fact that citric acid (also called citrate) is used in the process.The mitochondrial DNA is found within the matrix, often attached to the inner membrane. This DNA contains only 37 genes. These genes are responsible for the production of certain proteins used by the mitochondrion. These proteins are made by the ribosomes within the mitochondrial matrix. Mitochondrial DNA is similar to bacterial DNA.

Enzymes such as ATP synthase are encoded in mitochondrial DNA as seen in the following diagram:

The ribosomes in the matrix are similar in structure to ribosomes found in bacteria. This and the nature of mitochondrial DNA suggests that mitochondria were once free-living bacteria that took up permanent residence inside larger cells, becoming organelles in the process.

In essence, the mitochondrial matrix is the cytoplasm of the original bacterium. Chloroplasts in plant cells seem to have undergone a similar history. The process of smaller cells coming to live inside larger ones is called endosymbiosis.Although the mitochondrion’s ribosomes produce proteins, many proteins used by the mitochondrion are actually produced in the host cell outside the mitochondrion.

These proteins are encoded in the host cell’s DNA and made by the host cell’s ribosomes. However, the DNA that codes for these proteins probably migrated to the cell’s nucleus from the mitochondrion long ago. These proteins include ATP synthase, an enzyme necessary for making ATP.

The matrix also contains granules made of ions. The purpose of these granules is poorly understood, but they seem to be involved in maintaining the ionic balance of the mitochondrion.

Lesson Summary

Let’s review.The matrix is a gel-like material in the mitochondrion, or organelle that performs the process of aerobic respiration, that contains ribosomes resembling those of bacteria. It contains the mitochondrion’s DNA, which also resembles that of bacteria.

It has granules likely used for ionic balance in the cell and its density is greater than that of the cytoplasm surrounding the mitochondrion. Finally, the matrix is where the citric acid cycle takes place.


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