All organisms possess cellular organization and made up of one or more cells. The cellular structure is essential in performing various life processes. Each cell can be considered as the structural and functional unit of life.
All cells possess somewhat similar elemental and molecular constituents. They differ in their structural and ultra structural organization. Based on the differences in their structure, they are of two types prokaryotic cell and eukaryotic cell, and the organisms having such cells are respectively called prokaryotes and eukaryotes.
 |
| Cell structure of Prokaryotes and Eukaryotes |
1 . Prokaryotes -
Pro means primitive and karyon means nucleus. So basically, the word “prokaryote” means “before nucleus.”
Prokaryotes Include those organisms that are simple in cellular organization meaning the cells lack membrane enclosed organelles and possess a poorly defined nucleus, referred to as nuclear material which is also known as nucleoid.
Prokaryotic nucleus consists of only chromosomal DNA which are present in cytoplasm. Its nucleus is without nuclear membrane and nucleolus.
Prokaryotic cellular organization does not possess Internal membrane bound cell organelles such as mitochondria, Golgi body, plastids, endoplasmic reticulum etc. They do not possess any differentiated cells or tissues.
Prokaryotic cells are a lot smaller than eukaryotic cells and have a simpler structure. This simple structure is actually a good thing for prokaryotes, because it allows them to reproduce very quickly and very effectively.
Prokaryotes Include two groups of organisms - Bacteria and Achaea.
2. Eukaryotes -
Eu means true or real and karyon means nucleus. So in essence the word “eukaryote” means “true nucleus.”
Eukaryotes include those organisms that have well developed cellular organization meaning the cells possess membrane enclosed organelles and highly developed nucleus ( membrane - bound ) with nucleolus.
Eukaryotic cells are larger and much more complicated than prokaryotic cells.
| Feature | Prokaryotes. | Eukaryotes |
|---|---|---|
| Types of Nucleous | - Not true membrane bound nucleous. - Primitive - It is called nucleoid or chromatin material. |
- True membrane bound Nucleous |
| Nuclear membrane and nucleous | - Absent | - Present |
| Chromosome | - Usually, one circular chromosome. | - More than one linear chromosome occur in the nucleus |
| DNA | - Not complexed with proteins (histones). | - Complexed with basic proteins called histones. |
| Plasmids | - verry common | - Rare or absent |
| Arrangement of Genes |
- Linear | - Exons and Introns occur on chromosome |
| Cell wall | - Peptidoglycan occurs as major unit in cell wall. - archaea possess pseudomurein. |
- Peptidoglycan is absent - May lack cell wall or made up of either cellulose, chitin, keratin, etc |
| Cytoskeleton | - Rudimentary | - cytoskeleton consist of microfilaments, intermediate filaments and microtubules. |
| Ribosome | - Smaller (70S) | - Larger (80S) |
| Gas vesicles | - Present | - Not observed |
| Flagelia | - Submicroscopic in size. Consist of a single protein (Flagellin) filament. - Some possess axial filaments. |
- Microscopic in size. Membrane bound complex consist of multiple microtubules. - Some possess cilia. |
| Cell Size | - 0.2-2 μm x 2-8 μm | - Diameter greater than 5 μm. |
| Permeability of nuclear membrane | - not present | - selectively permeable |
| Chloroplast | - Absent | - Present in plants |
| Mitochondria | - Absent | - Present in animals and fungi |
| Lysosomes and peroxisomes | - Absent | - Present |
| Genetic recombination | - Partial, undirectional transfers DNA. | - Meiosis and fusion of gametes |
| Mode of cell division | - Binary Fission | - Mitosis occurs in somatic (body) cells and meiosis occurs during formation of gametes. |
| Metabolism | - Exhibit a great diversity of metabolic pathways. - Some are strictly or facultative anaerobic. |
- Follow a common pattern. Glycolysis occurs commonly in most organisms. - Mainly aerobic respiration, very few are anaerobic. |
| Occurrence | - Occurs in diverse ecosystems that provide nutrient. | - Found in diverse habitats as per availability of favourable conditions. |
| Phylogenetic groups included | - Domain : Bacteria and Archaea | - Domain - Eukarya, includes Protista, animalia, plantae, fungi |
Defferences between Prokaryotic and Eukaryotic cell
• Prokaryotic cells are the oldest type of cell. They are small and relatively simple.
Eukaryotic cells evolved from prokaryotic cells later. They are larger and much more complex internally.
• Prokaryotes lack both a nucleus and membrane-bound organelles.
Eukaryotic cells have a nucleus, and also contain organelles.
• Prokaryotes are single-celled organisms.
Eukaryotes can be either single-celled or multicellular.
• The DNA of a prokaryote is usually organized as a single, circular chromosome, while the DNA of a eukaryote is organized as linear chromosomes.
