Comparison of Structure and Function of 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.
(Image will be uploaded soon)
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.
(Image will be uploaded soon)
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.
FAQs on Difference Between Mitochondria and Chloroplasts in Cells
1. What is the main difference between mitochondria and chloroplasts?
The main difference between mitochondria and chloroplasts is that mitochondria carry out cellular respiration to produce ATP, while chloroplasts perform photosynthesis to make glucose.
- Mitochondria convert glucose and oxygen into ATP, carbon dioxide, and water.
- Chloroplasts use sunlight, carbon dioxide, and water to produce glucose and oxygen.
- Mitochondria are found in almost all eukaryotic cells, whereas chloroplasts are found only in plant cells and some protists.
2. What is the function of mitochondria in a cell?
The primary function of mitochondria is to produce energy in the form of ATP (adenosine triphosphate) through cellular respiration.
- They break down glucose during glycolysis, Krebs cycle, and electron transport chain.
- They are known as the “powerhouse of the cell.”
- They regulate cell metabolism and help control programmed cell death.
3. What is the function of chloroplasts in plant cells?
The main function of chloroplasts is to perform photosynthesis, converting light energy into chemical energy stored as glucose.
- They contain chlorophyll, the green pigment that absorbs sunlight.
- Photosynthesis occurs in two stages: light reactions and the Calvin cycle.
- They produce oxygen as a byproduct.
4. Do mitochondria and chloroplasts have their own DNA?
Yes, both mitochondria and chloroplasts contain their own circular DNA and ribosomes.
- This supports the endosymbiotic theory.
- They can replicate independently of the nucleus.
- Their DNA codes for some of their own proteins.
5. How are the structures of mitochondria and chloroplasts different?
The structure of mitochondria differs from chloroplasts mainly in their internal membrane organization and pigments.
- Mitochondria have an inner membrane folded into cristae and a central matrix.
- Chloroplasts contain stacked membranes called thylakoids forming grana, surrounded by stroma.
- Chloroplasts contain chlorophyll, while mitochondria do not.
6. Are mitochondria and chloroplasts found in all cells?
Mitochondria are found in most eukaryotic cells, but chloroplasts are present only in plant cells and some algae.
- Animal cells have mitochondria but lack chloroplasts.
- Plant cells contain both mitochondria and chloroplasts.
- Prokaryotic cells lack both organelles.
7. Why are mitochondria called the powerhouse of the cell?
Mitochondria are called the powerhouse of the cell because they generate most of the cell’s ATP through cellular respiration.
- ATP is the main energy currency of the cell.
- The electron transport chain in the inner membrane produces large amounts of ATP.
- Without mitochondria, cells cannot meet their energy demands.
8. How do mitochondria and chloroplasts work together in plant cells?
In plant cells, chloroplasts produce glucose by photosynthesis, and mitochondria use that glucose to generate ATP.
- Chloroplasts make glucose and oxygen.
- Mitochondria use glucose and oxygen for cellular respiration.
- This forms an energy cycle between photosynthesis and respiration.
9. What are the similarities between mitochondria and chloroplasts?
Mitochondria and chloroplasts are similar because both are double-membraned organelles that produce energy and contain their own DNA.
- Both have circular DNA and 70S ribosomes.
- Both generate ATP through membrane-based processes.
- Both support the endosymbiotic theory of origin.
10. What is the endosymbiotic theory for mitochondria and chloroplasts?
The endosymbiotic theory states that mitochondria and chloroplasts originated from free-living prokaryotic cells that were engulfed by ancestral eukaryotic cells.
- Mitochondria likely evolved from aerobic bacteria.
- Chloroplasts likely evolved from photosynthetic cyanobacteria.
- Their own DNA and double membranes support this theory.
