What Sets Mitochondria and Plastids Apart in Cell Biology?
Two organelles found in cells are chloroplasts and mitochondria. Only algae and plant cells have the membrane-bound organelle known as the chloroplast. Eukaryotic cells in animals, plants, and fungi all have mitochondria. The primary distinction between chloroplasts and mitochondria is how they work. While mitochondria are the powerhouses of the cell, breaking down sugar to release energy through cellular respiration, chloroplasts are responsible for producing carbohydrates with the help of sunlight.
What are Mitochondria?
All eukaryotic cells have a membrane-bound organelle called a mitochondrion. The mitochondria produce ATP, which serves as the cell's chemical energy source. Inside the organelle of the mitochondria is their own DNA.
Structure of Mitochondria
A mitochondrion is a bean-shaped structure with a diameter of 0.75m to 3m. Depending on the cell type, tissue, and organism, a given cell may have one or several mitochondria. While the inner membrane is deeply folded, the outer membrane is porous. However, these folds enhance the surface area for chemical processes that produce ATP. The mitochondria release these energies, which are needed for a variety of chemical reactions, in the form of ATP (Adenosine triphosphate) molecules.
Porins are numerous integral membrane proteins found throughout the outer mitochondrial membrane. An outer membrane protein is a translocase. The N-terminal signal sequence of big proteins that are translocase-bound permits the protein to reach mitochondria. MAM is a structure created by the union of the mitochondrial outer membrane and endoplasmic reticulum (mitochondria-associated ER-membrane). Through calcium signalling, MAM enables the transfer of lipids between mitochondria and the ER.
There are more than 151 protein types in the inner mitochondrial membrane, and they all play various roles in the body. It lacks porins; the inner membrane's translocase is of the TIC complex type. Between the inner and outer mitochondrial membranes is the intermembrane gap.
The matrix is the area where the two mitochondrial membranes encompass. In the matrix are ribosomes with a variety of enzymes and mitochondrial DNA. DNA found in mitochondria is a circular molecule. The DNA is about 16 kb in size and contains 37 genes. The DNA of mitochondria may be present in the organelle in 2–10 copies. Cristae, or folds of the inner mitochondrial membrane, are formed in the matrix. Cristae expand the surface area of the inner membrane.
Function of Mitochondria
Respiration is the mechanism by which mitochondria convert chemical energy into ATP for use in cellular processes. Other mitochondrial functions include control of cellular metabolism, steroid synthesis, calcium storage in the cell for signal transduction, cell membrane potential control, utilizing reactive oxygen species for signalling, the heme synthesis pathway's production of porphyrin, hormonal communication and control over apoptosis.
What are Plastids?
Algal and plant cells include plastids known as chloroplasts. To perform photosynthesis, they have chlorophyll pigments. Their own DNA is found in the chloroplast. The creation of organic molecules, specifically glucose from CO2 and water with the help of sunshine, is the primary activity of the chloroplast.
Types of Plastids
Chromoplasts and leucoplasts are two different forms of plastids. Chloroplasts are pigments that include chlorophyll. Chloroplasts play a crucial role in photosynthesis in plants, though. However, in addition to chlorophyll, the chloroplasts also contain yellow or orange pigments. Oils, carbohydrates, and protein granules are generally stored in leucoplasts, which are organelles.
Function of Plastids
Plant stems, cactus, and leaves all contain chloroplasts. Chlorenchyma is the name of a chlorophyll-rich plant cell. Depending on the amount of sunlight present, chloroplasts can change their orientation. In a process known as photosynthesis, chloroplasts can convert carbon dioxide and water into glucose with the help of light energy. The two steps of photosynthesis are the light reaction and the dark reaction.
Difference Between Mitochondria and Plastids
Occurrence: Mitochondria are found in eukaryotic cells, while plastids are found in plant cells.
Function: Cell respiration is mitochondria's primary function, while the main photosynthesis organelle in plants are plastids
Pigments: Mitochondria is devoid of pigments, while pigments are present in plastids.
Size: Mitochondria are small in size, while plastids are huge in size.
ATP: Mitochondria aid in ATP production, while plastids aid in the synthesis of glucose.
Interesting Facts
The inner membrane and the outer membrane are the two membranes that cover the mitochondria.
The primary distinction between mitochondria and chloroplasts relates to how they function.
The primary distinction between plastids and mitochondria is that plastids are found solely in plants, whereas mitochondria are found in all eukaryotic cells. Plastid, on the other hand, has a disc-like form, whereas mitochondria are shaped like beans.
Important Questions
1. What is ATP?
Ans: At the cellular level, energy is used and stored as adenosine triphosphate (ATP).
2. What is the function of leucoplasts?
Ans: Leucoplasts’ primary purpose is to store vital substances such as proteins, lipids, and starches.
Key Features
Both mitochondria and chloroplasts are membrane-bound organelles involved in energy conversion.
During photosynthesis, light energy is stored in chloroplasts in the chemical bonds of glucose. In order for ATP to be utilised in cellular functions, mitochondria transform the light energy held in glucose into chemical energy called cellular respiration. Carbon dioxide and oxygen are used in the operations of both organelles.
Endosymbiotic relationships are thought to have given rise to both organelles. Their DNA is unique to them.
FAQs on Mitochondria vs Plastids: Essential Differences for Students
1. What is the primary difference between mitochondria and plastids based on their function?
The primary difference lies in their core functions. Mitochondria are known as the 'powerhouses of the cell' because they perform cellular respiration to break down glucose and produce energy in the form of ATP. In contrast, plastids are mainly involved in manufacturing and storing food. The most common type, chloroplasts, perform photosynthesis to create glucose.
2. In which types of cells are mitochondria and plastids found?
Mitochondria are found in the cytoplasm of virtually all eukaryotic cells, including both plant and animal cells. Plastids, however, are a distinctive feature of plant cells and algae; they are absent in animal cells and fungi.
3. How do the internal structures of mitochondria and plastids (chloroplasts) differ?
Both are double-membraned, but their internal membrane systems are different. In mitochondria, the inner membrane is folded into finger-like projections called cristae, which increase the surface area for ATP production. In chloroplasts (a type of plastid), the internal membrane system consists of flattened sacs called thylakoids, which are often stacked into structures known as grana. These thylakoids are the site of photosynthesis.
4. What are the different types of plastids and their importance?
Plastids are classified based on the pigments they contain and their function. The main types are:
- Chloroplasts: Contain chlorophyll and are the site of photosynthesis.
- Chromoplasts: Contain carotenoid pigments, which give flowers and fruits their yellow, orange, or red colours, aiding in pollination and seed dispersal.
- Leucoplasts: Are colourless plastids that store nutrients. They include amyloplasts (store starch), elaioplasts (store oils), and proteinoplasts (store proteins).
5. What are the key similarities between mitochondria and plastids?
Despite their different functions, mitochondria and plastids share several remarkable similarities, which support the endosymbiotic theory. Both organelles:
- Possess a double membrane.
- Contain their own circular DNA, separate from the cell's nuclear DNA.
- Have their own ribosomes (70S type), similar to those in prokaryotes.
- Are semi-autonomous and can replicate independently of the cell cycle through binary fission.
6. Why do plant cells need both mitochondria and plastids to survive?
Plant cells require both because their functions are complementary, not mutually exclusive. Plastids (chloroplasts) produce glucose through photosynthesis using light energy. However, this glucose is just a storage molecule. The cell needs mitochondria to break down this glucose through cellular respiration to release usable energy (ATP) for all metabolic activities, such as growth, repair, and transport. This energy is required 24/7, even when photosynthesis is not occurring at night.
7. Is there a difference between the terms 'mitochondrion' and 'mitochondria'?
Yes, the difference is grammatical. 'Mitochondrion' is the singular form, referring to a single powerhouse organelle. 'Mitochondria' is the plural form, used when referring to two or more of these organelles. For example, a single liver cell can contain over a thousand mitochondria.
8. How does the endosymbiotic theory explain the origin of mitochondria and plastids?
The endosymbiotic theory proposes that both mitochondria and plastids were once free-living prokaryotic organisms. It is believed that an early anaerobic eukaryotic cell engulfed an aerobic bacterium (which evolved into a mitochondrion) and, in the lineage leading to plants, also engulfed a photosynthetic cyanobacterium (which evolved into a plastid). Instead of being digested, they formed a symbiotic relationship with the host cell. The presence of their own DNA, double membranes, and prokaryote-like ribosomes strongly supports this theory.
