Roger Y. Stanier and his colleagues came up with two categories of living organisms. This categorization was based on the type of nucleus present in their cells. The two categories are: (A) Prokaryotic cells – These are simple cells that do not have a nucleus or other organelles enclosed by a membrane. (B) Eukaryotic cells – These are complex cells that have a true nucleus and other membrane-bound organelles. So, organisms with prokaryotic cells are prokaryotes. Organisms with eukaryotic cells are eukaryotes. This article focuses on difference between prokaryotic and eukaryotic cell.
Microbes can be broadly classified into two groups based on their caryone (nucleus) structure:
- Prokaryotes: Prokaryotes are microbes that lack a true nucleus and other membrane-bound organelles. The genetic material in a prokaryotic cell is contained within a single, circular DNA molecule located in the cytoplasm. Prokaryotes include bacteria and archaea.
- Eukaryotes: Eukaryotes are microbes that have a true nucleus and other membrane-bound organelles. The genetic material in a eukaryotic cell is contained within a distinct nucleus, separated from the cytoplasm by a nuclear membrane. Eukaryotes include a wide range of organisms, such as animals, plants, fungi, and protists.
This classification based on Nucleus (caryon) structure is important because it reflects fundamental differences in the organization and function of these microbes, which have significant implications for their biology, ecology, and evolution.
Eukaryotic Cell Structure
Eukaryotic cells are much more complex than prokaryotic cells due to the presence of various distinct structures. In contrast to prokaryotic cells, which lack a distinct nucleus and membrane-bound organelles, eukaryotic cells have a range of essential structures that enable them to perform a wider variety of functions and carry out more complex processes.
Cell Wall:
The cell wall is a rigid layer that surrounds the cell membrane of prokaryotic cells. It provides structural support and protection against changes in osmotic pressure. The composition of the cell wall varies among different types of prokaryotes. Bacteria have cell walls made of peptidoglycan, while archaea have cell walls made of other types of molecules such as pseudopeptidoglycan or S-layer proteins.
Cell Membrane:
The cell membrane of prokaryotic cells is a lipid bilayer that encloses the cytoplasm and separates it from the outside environment. composed of phospholipids and proteins and regulates the movement of molecules in and out of the cell. Some prokaryotes may also have specialized structures like hopanoids that help maintain the membrane’s stability.
Cytoplasm:
The cytoplasm is the gel-like substance that fills the interior of the prokaryotic cell. It contains various structures like ribosomes, inclusion bodies, gas vesicles, and other enzymes necessary for the cell’s survival. Additionally, it also contains the nucleoid, which is the region where the genetic material of the cell is located.
Ribosomes:
Ribosomes are responsible for protein synthesis in prokaryotic cells. They are composed of RNA and proteins and are typically smaller than ribosomes found in eukaryotic cells. Ribosomes in prokaryotic cells are referred to as 70S ribosomes and are composed of a smaller 30S subunit and a larger 50S subunit.
Nuclear Region:
The nuclear region, or nucleoid, is where the genetic material of prokaryotic cells is located. Unlike eukaryotic cells, it is not enclosed by a membrane. The DNA is present in a circular, double-stranded molecule called a chromosome. Some prokaryotes have plasmids, which are smaller, circular molecules of DNA that can be exchanged between cells and often carry genes for antibiotic resistance or other traits.
Eukaryotic Cell Structure
Eukaryotic cells are cells that have a distinct nucleus enclosed by a membrane, as well as other membrane-bound organelles. Here are some details about the main structures of a eukaryotic cell:
1. Cell wall
Plant cells, for example, have a cell wall made of cellulose. Cell wall provides structural support and protection to some eukaryotic cells, such as plant cells.
2. Cell membrane:
The cell membrane is a thin, flexible barrier that surrounds the cell, separating the internal environment from the external environment. The cell membrane, composed of a phospholipid bilayer and proteins. It regulates the movement of substances in and out of the cell.
3. Nucleus:
The nucleus is the most prominent organelle in a eukaryotic cell. The nucleus contains the cell’s genetic material (DNA) in the form of chromosomes, organized into a distinct structure called the nucleolus. The nuclear envelope encloses the nucleus with its double membrane, containing pores that enable the exchange of materials between the nucleus and the cytoplasm.
4. Cytoplasm:
The cytoplasm is the gel-like substance that fills the cell. containing all of the cell’s organelles and other structures are present in cytoplasm. .
5. Ribosomes:
Ribosomes are the site of protein synthesis in a cell. They are small, spherical structures that are either free in the cytoplasm or attached to the endoplasmic reticulum.
6. Endoplasmic reticulum:
The endoplasmic reticulum (ER) is a network of flattened sacs and tubules. It is responsible for protein and lipid synthesis, and it transports these molecules within the cell. The ER can be either smooth or rough, depending on whether it has ribosomes attached to its surface.
7. Golgi apparatus:
The Golgi apparatus, a stack of flattened membrane-bound sacs, processes and modifies proteins and lipids synthesized in the ER, packaging these molecules into vesicles for transport to other parts of the cell or for secretion outside the cell. It packages these molecules into vesicles for transport to other parts of the cell or for secretion outside the cell.
8. Mitochondria:
Mitochondria generate most of the cell’s energy through cellular respiration. Scientists believe that they originated from symbiotic bacteria that eukaryotic cells incorporated. Mitochondria have their own DNA.
Chloroplasts:
Chloroplasts, found in plant cells, are responsible for photosynthesis, converting sunlight into energy, and also have their own DNA, thought to have originated from symbiotic bacteria.
Overall, eukaryotic cells are much more complex than prokaryotic cells, which lack a distinct nucleus and membrane-bound organelles. The presence of these structures allows eukaryotic cells to perform a wider variety of functions and carry out more complex processes.
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