It has been found that most protists possess mitochondria and its associated DNA and enzymes. The main function of mitochondria in protists is respiration and energy supply, from genome sequencing studies over the past decade.
Let us find out if protists can have mitochondria, the number of mitochondria they have, its relevance and function, and other related facts in this article.
Can protists have mitochondria?
Mitochondria is a vital organelle needed for the survival of cells of all living organisms. Let us see if protists can have mitochondria.
Most protists that require aerobic respiration for survival have mitochondria in their cell. This is important for the supply of oxygen and energy to the eukaryotic cells.
Some example of protists with mitochondria are algae, amoeba, Euglena and Dianoflagellates.
Do all protists have mitochondria?
Though mitochondria is required for respiration in all eukaryotic organisms, that is not true in case of all protists. Let us find that out in details.
Only the protists that require oxygen for survival through aerobic respiration have mitochondria. The other types of protists which do anaerobic respiration do not have mitochondria.
The main function of mitochondria is to break down food to supply chemical energy using oxygen. So without oxygen the anaerobic protists have adapted their cellular respiration to supply energy from other cell compartments without the use of mitochondria.
For example Nictotherus ovalis that lives in cockroach hindgut contains Hydrogenosomes.
Why do all protist does not have a mitochondria?
There are a class of protists that are generally parasitic in nature or reside in sulfur zones of marine sediments, and thus inhabit in places without free oxygen. So they supply ATP through substrate level phosphorylation and create hydrogen as by-product.
How many mitochondria are in a protist cell?
Since mitochondria is a necessary organelle in most protists that do aerobic metabolism, let us find out how many mitochondria does a protest cell contain.
Protist cells like other eukaryotic cells my contain one to several thousand mitochondria depending upon the cell respiration rate. Normally Protist cells have maximum of five thousand mitochondria per cell.
For example, Euglena has a single large mitochondria per cell, while Parameocium can have five thousand and algal cells have generally more than one mitochondria.
Why do protists have mitochondria?
Now that we know mitochondria is present in the cytoplasm of the protist cell, let us learn the significance of the organelle inside the cell.
The most supported hypothesis for the presence of mitochondria in protists, is the Endosymbiotic theory which is discussed below:
- According to this, early prokaryotic organisms acquired some other bacterial species and retained them via endosymbiosis which evolved into eukaryotic cells with mitochondria.
- From genome sequencing studies it has been found that certain organelles like mitochondria, chloroplast have their own genetic materials but their genome are reduced in size.
- Thus scientists believe that during evolution through endosymbiosis, the host cells acquired the ability to compartmentalize their organelles for better production of energy. And these cells evolved to become eukaryotes like protists.
What is the function of mitochondria in protist?
Sequencing studies of the mitochondrial DNA has revealed that protists share similarities to plant mitochondrial genome than with animals or fungi. Let us now see its function.
The different functions of mitochondrion in protits is discussed below:
- To perform cellular respiration and oxidative phosphorylation where pyruvate is broken down to supply ATP to the cells.
- Mitochondria stores calcium ions thereby maintaining calcium homeostasis and also helps in signal transduction.
- Mitochondria is the seat of citric acid cycle and electron transport chain and regulates cellular metabolism.
- It also regulates cell cycle through oxidative phosphorylation and apoptosis.
- Mitochondria pumps protons and maintains membrane potential.
Do protist cells lack mitochondria?
We know mitochondria is required by most protists to carry out important cellular metabolism. Now let us see if they survive without mitochondria.
The protists that are anaerobes and do not require oxygen for respiration lack mitochondria. Instead they have specialized structures called Hydrogenosomes to supply energy.
The hydrogenosomes are unique structures that supplement the function of mitochondria in parasitic protists. These are membrane bound organelles that sequester chemical energy by enzymes and releasing hydrogen instead of oxygen.
Can protists survive without mitochondria?
Protists have unique cellular organization depending upon their metabolic requirements. So let us find out if they can survive without mitochondria.
The protists which are dependent on oxidative phosphorylation for ATP synthesis and oxygen supply cannot survive without mitochondria. Only the class of anaerobic protists which have evolved to escape oxygen dependency by using Hydrogenosomes can survive without mitochondria.
From this article, it can be concluded that protists possess mitochondria for cellular respiration and energy supply and only a subclass of them do not require mitochondria because they do not use oxygen for respiration, yet get ATP through another organelle.