The structure and function of mitochondria are elaborated below.
What is a mitochondria?
Mitochondria word is made up of two Greek words “mitos” meaning "thread" and “chondros” meaning “granule”. Mitochondria (mitochondrion: singular) is a double membrane-bounded organelle present in a eukaryotic cell. It is known as the “powerhouse” of the cell as most of the energy is produced inside the mitochondria. It was first discovered by physiologist Albert von Kolliker in 1857. In 1886 Richard Altman called it “bioblasts” (life germs) which was later renamed as “mitochondria” by Carl Benda.
Structure of mitochondria
The mitochondria consist of the outer membrane, inner membrane, cristae, matrix, mitochondrial DNA, and ribosomes.
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| A diagram of mitochondrion. Image created in BioRender.com |
Outer mitochondrial membrane
The outer mitochondrial membrane is involved in the movement of ions in and out of mitochondria due to the presence of porin proteins. It also contains enzymes responsible for fatty acid elongation and adrenaline oxidation.
Intermembrane space
The space present between the outer and inner membrane of mitochondria is called intermembrane space. It plays important role in the regulation of respiration.
Inner mitochondrial membrane
The inner mitochondrial membrane consists of several enzymes. It contains ATP synthase which produces ATP (adenosine triphosphate) and transport proteins that control the movement of substances in and out of the matrix.
Matrix
The space present inside the inner mitochondrial membrane is called a matrix. It is the main site of aerobic respiration, Krebs cycle or TCA and fatty acid cycles. It contains enzymes, RNA, DNA, and ribosomes.
Cristae
Unlike the outer membrane, the inner membrane forms several folds known as cristae. It gives a wrinkle like appearance to the inner membrane. It increases the surface area for the chemical reactions to take place such as oxidative phosphorylation.
Mitochondrial DNA
Mitochondria has its own DNA known as mitochondrial DNA (mtDNA), hence it is a self-replicating organelle. Mitochondrial DNA is a small circular DNA present transferred from mother cell to daughter cells. It contains genes for the synthesis of enzymes involved in energy-producing pathways.
Ribosomes
Ribosomes in mitochondria are involved in the synthesis of proteins.
Functions of mitochondria
The main functions of mitochondria are:- Mitochondria are a powerhouse of the cell and site for the production of ATP. It converts ADP into ATP. ATPs are known as “energy currency” and provide energy during chemical reactions. The more the mitochondria in a cell, the more the ATP.
- It is also involved in heat generation in the brown adipose tissue using the electron transport chain.
- It plays important role in cell death by apoptosis.
- It absorbs and stores calcium ions.
Video lesson
Origin of mitochondria
Mitochondria are thought to be evolved from engulfing of prokaryotes. The theory which explains the origin of mitochondria is called an endosymbiotic theory. According to this theory, an aerobic independent free-living prokaryotic cell was engulfed by a eukaryotic cell and instead of digesting it, they both developed a symbiotic relationship with each other. The prokaryotic cell provided energy to the eukaryotic cell and eventually developed into an organelle. On the other hand, the eukaryotic cell provided space and protection to the prokaryotic cell. This process took millions of years and the presence of prokaryotic cell or mitochondria became a distinguishing feature for the eukaryotic cell.
This theory is also suitable to explain the presence of DNA in mitochondria which are separate from DNA in the nucleus. The DNA present in mitochondria is thought to be the DNA of the engulfed prokaryotic cell, which resides inside the cell and is finally called mtDNA. The mtDNA is circular just like prokaryotic DNA.
MtDNA is passed from mother to next generation as sperm cells lack cytoplasm and mitochondria. New mitochondria are formed by binary fission from the preexisting mitochondria. So if all the mitochondria are removed from a cell that cell cannot regenerate mitochondria.
Some questions and answer
1. Which part of mitochondria is responsible for aerobic respiration?
A. Intermembrane space
B. Inner mitochondrial membrane
C. Matrix
D. Cristae
Correct Answer: C
2. Which of the following is not the function of mitochondria?
A. ATP production
B. Protein synthesis
C. Heat generation
D. Absorption of calcium ions
Correct Answer: B
3. Select the incorrect statement
A. Mitochondrion is a self-replicating organelle
B. mtDNA comes from engulfed prokaryotic cell
C. Mitochondrion is a powerhouse of the cell
D. Mitochondria lack enzymes for fatty acid synthesis
Correct Answer: D
4. mtDNA is transferred from …….. to next generation
A. Egg cell
B. Sperm cell
C. Both A and B
D. None of the above
Correct Answer: A
5. Which theory explains the origin of mitochondria?
A. Theory of evolution
B. Cell theory
C. Germ theory
D. Endosymbiotic theory
Correct Answer: D
6. Inner mitochondria membrane contains
A. Phosphorylase
B. ATP synthase
C. Sulfatases
D. Protease
Correct Answer: B
7. Mitochondria are divided by …………
A. Fusion
B. Binary fission
C. Meiosis
D. Binary fusion
Correct Answer: D
8. Which part of mitochondria controls the movement of ions?
A. Outer mitochondrial membrane
B. Inner mitochondrial membrane
C. Matrix
D. Cristae
Correct Answer: A
9. Which part gives a wrinkle-like appearance to mitochondria?
A. Outer mitochondrial membrane
B. Inner mitochondrial membrane
C. Matrix
D. Intermembrane space
Correct Answer: B
10. The inner membrane of mitochondria folds is called ……….
A. Thylakoids
B. Cristae
C. Matrix
D. Grana
Correct Answer: B
References
- Gray, M. W., Burger, G., & Lang, B. F. (1999). Mitochondrial evolution. Science, 283(5407), 1476-1481.
- Sherratt, H. S. (1991). Mitochondria: structure and function. Revue neurologique, 147(6-7), 417-430.
- Picard, M., Taivassalo, T., Gouspillou, G., & Hepple, R. T. (2011). Mitochondria: isolation, structure and function. The Journal of physiology, 589(18), 4413-4421.
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