Difference Between Mitochondria and Chloroplasts

A eukaryotic cell has only three organelles that have a double-layered structure, namely, nucleus, mitochondria, and chloroplast., Here, we will discuss the two organelles of eukaryotic cells , mitochondria and chloroplasts, and their differences. Mitochondria and chloroplast are semiautonomous organelles that share various structural similarities but the major difference is their occurrence. Mitochondria are found in eukaryotic animal cells, whereas chloroplasts are found in plant cells. 

Mitochondria

Mitochondria are membrane-bound organelles found in almost all eukaryotic organisms. Their primary function is to generate energy in the form of adenosine triphosphate (ATP). It is commonly called a powerhouse of the cell. Additionally, they are able to generate heat, store calcium for cell signalling activities, cellular differentiation, mediate the cell cycle, and promote cell growth. Each human cell contains on average 100-1000 mitochondria.

Almost all the genetic material is stored in every cell’s nucleus. Mitochondria have their own DNA and ribosomes. In most organisms, the Mitochondrial DNA is inherited maternally. The number of mitochondria varies in different organisms, tissues, and cell types. Usually, there are multiple mitochondria found in one cell depending on its function.

Structure of Mitochondria

Mitochondria have a double-layered membrane. They are rod-shaped or sausage-shaped organelles measuring 0.5-10μm in length. In a typical cell, they occupy almost 25% of the cell volume. Earlier mitochondria were represented as individual isolated organelles, now they form a dynamic connected network also called a reticulum. It has four main compartments mentioned below.

• Outer Membrane- It is permeable to certain ions and small molecules.

• Intermembrane Space- It has a composition similar to the cytosol.

• Inner Membrane- In this, respiratory chain proteins are found and are folded into multiple cristae allowing larger space to hold proteins involved in electron transport chains.

• Both outer and inner membranes are made up of phospholipid layers just like the cell’s outer membrane.

• Matrix - It is the inner part of the mitochondria, where the metabolic reactions take place.

• The mitochondrial DNA resides in its matrix. Also, it is small and circular.

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Functions of Mitochondria

Mitochondria are essential for aerobic metabolism. They are responsible for energy production through oxidative phosphorylation. Almost 90% of the cell’s energy is produced by them. They convert nutrients into Adenosine TriPhosphate (ATP) in the presence of oxygen (aerobic respiration). They maintain, replicate, and transcribe their own DNA. They are also involved in the synthesis of iron-sulfur clusters.

Chloroplasts

Chloroplast is an organelle found in plants and green algae. It is a type of plastid that contains chlorophyll to absorb solar energy. It is green in colour due to the presence of two pigments -chlorophyll a and chlorophyll b. The chloroplast is a double-layered cell organelle. It is a semi-autonomous organelle that has its own DNA. It also contains thylakoids. The number of chloroplasts varies in different cells. Plants growing in shade contain larger chloroplasts in their cells than those which grow in intense light.

Structure of Chloroplasts 

Chloroplasts differ in shape being plate-shaped in Chlorella, cup-shaped in Chlamydomonas, and in higher plants, they are spherical or ovoid. They measure  4-6μm in size. The chloroplasts  have the following parts:

• Outer Membrane - It is a semi-porous membrane, permeable to small molecules and ions. It is not permeable to large proteins.

• Intermembrane space

• Inner Membrane - It regulates the passage of materials in and out of the chloroplast.

• Stroma - It is an aqueous, alkaline fluid that is protein-rich and is present within the inner membrane. The chloroplast DNA, chloroplast ribosomes, starch ribosomes, thylakoid system, and many proteins are found floating in the stroma.

• Thylakoid - The thylakoid system is suspended in the stroma and is a collection of membranous sacs called thylakoids. The chlorophyll is stored in thylakoids and is the site for the process of light reactions to take place in photosynthesis. The thylakoids are arranged in stacks known as Grana. Each Grana contains 10-20 thylakoids.

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Functions of Chloroplast 

Chloroplasts are the sites for photosynthesis where reactions take place to harness solar energy and convert it into chemical energy. They also carry out functions like the synthesis of fatty acids, amino acids, and membrane lipids. Plants do not have specialized immune cells, all cells participate in plant response.

Mentioned below is the table that enlists the difference between mitochondria and chloroplast based on different parameters. 

Difference Between Mitochondria and Chloroplasts

Here, we learned about mitochondria, their structure, and their function. We have also learned about chloroplast structure and function. The difference between these semi-autonomous organelles is also covered in the article.