A Eukaryotic cell has only three organelles that have a double-layered structure- nucleus, mitochondria, and chloroplast. In this section, we will consider the two units of eukaryotic cell i.e Mitochondria and Chloroplasts, and their differences.
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, mediating the cell cycle, and promoting cell growth and death. Each human cell contains on average 100-1000 mitochondria. A single mitochondria is called the mitochondrion.
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.
Mitochondria have a double-layered membrane. They are rod-shaped or sausage-shaped organelles measuring 0.5-10μm in length. In a typical cell, it occupies 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
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 is 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.
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.
The 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 consists of membrane-bound structures called Thylakoids which are the site of light-dependent reactions. It has its own DNA like mitochondria and is involved in energy metabolism.
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.
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.
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.
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.
1. How do mitochondria and chloroplasts work together?
Chloroplasts are responsible for converting sunlight into food for plants by a process known as photosynthesis. Further, mitochondria are responsible for converting this food into energy in the form of ATP. Here chemical reactions take place in the cell that allows the release of energy from food.
2. What are the similarities between mitochondria and chloroplasts?
Below is the similarities between mitochondria and chloroplasts:
Both these organelles are found in the cells of plants but in animal cells, only mitochondria are observed.
Both chloroplasts and mitochondria are responsible for generating energy for the cells they reside in.
The structure of both organelles comprises an inner and outer membrane.