Prokaryotic and Eukaryotic Cells

The concept of “cell” was first presumed to have occurred when an RNA molecule which is self-replicating in nature was enclosed within a membrane build-up of phospholipids. Cells can be classified broadly into two categories: Prokaryotic cells, which includes single-celled organisms of domain Bacteria and Archae; they are considered to be the simplest form of cells and Eukaryotic cells: Animal and Plant cells, fungi, protists. They are complex in their structural organisation. These two categories of cells represent the most fundamental evolutionary separation process and form the basis of classification of the living organisms in the world.1,3,4

Differences:

Prokaryotic cells:

Prokaryotic cells are the simplest form of cells lacking an organised structure called the nucleus and also other any membrane-bound organelle such as golgi bodies, mitochondria, chloroplast, lysosome, endoplasmic reticulum (ER). The genetic material, i.e., DNA (deoxyribonucleic acid) is present in the central region of cell darkened in nature known as nucleoid and is usually a single chromosome. They are haploid. The size of the cell ranges between 1 to 10µm. The reproduction processes of cells are asexual such as through budding or binary fission. Translational machinery consists of 70S ribosome (50S large subunit and 30S small subunit) and is freely distributed within the cytoplasm as ER is absent. Flagella are present as organs for locomotion and pili is also found in certain bacteria as an organ of attachment promoting virulence eg. in Neisseria gonorrhoeae. Both the transcription process (formation of mRNA from DNA) and translation process (the protein synthesis step) occurs in the cytoplasm. Process of phagocytosis or endocytosis as an immunologic response is completely absent among prokaryotic cells. The exchange of genetic material occurs through processes like transduction, conjugation and transformation. The regulatory mechanism of DNA is also very simple in comparison to eukaryotes. Extrachromosomal DNA such as plasmid conferring additional traits such as antibiotic resistance is usually observed among most of the organisms.

Eukaryotic cells:

They are complex in the organisation as they have a well-defined nucleus and other membrane-bound specialized organelles. They are diploid in nature and chromosome number is more than one. The size of the cell ranges lies usually within 5 - 100 µm. Cell division occurs through mitosis (in somatic cells) and meiosis (in gamete cells). The ribosome is the 80S (60S larger subunit and 40S smaller subunit) and is found both inbound (with ER) and free state (cytoplasm). Structures like flagella and pili are absent in eukaryotic cells. Exchange of genetic material occurs during meiotic cell division process. Endocytosis of phagocytosis can be observed among eukaryotic cells as a part of the immunological phenomenon. Plasmids are absent. 2,5

Certain differences between prokaryotic and eukaryotic cells that help in targeted therapy against bacterial infections are antibiotics targeting the bacterial cell wall biosynthetic process, e.g., Penicillin; antibiotics targeting the protein synthesis process of bacteria due to the difference in the ribosomal subunits, e.g., Tetracyclines and aminoglycosides; antibiotics that target the prokaryotic nucleic acid synthesis process, e.g., fluoroquinolones, rifamycin; antibiotics targeting the folic acid and mycolic acid synthesis of specific bacteria, e.g., sulfonamides. Bacterial cells can be grown in different agar-based media both fastidious (bacterial cells requiring special growth conditions, such as blood agar media, brain heart infusion agar) and non-fastidious (such as nutrient agar and Mueller Hinton agar media having carbon and nitrogen source) in nature. Eukaryotic cells, on the other hand, have special requirements such as amino acids, vitamins, hormones, carbohydrate source, protein source, serum and inorganic salts, exact carbon dioxide and pH requirement to create an in vivo conditions e.g., Minimum essential medium (MEM), RPMI1640, DMEM.6,7,8,9

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References:

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Chopra AD, Ra I. Understanding antibacterial action and resistance. Ellis Horwood Limited, London, United Kingdom; 1996.

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Basu S, Bose C, Ojha N, Das N, Das J, Pal M, Khurana S. Evolution of bacterial and fungal growth media. Bioinformation. 2015;11(4):182.