Friday, July 23, 2021

Major Differences between Prokaryotic and Eukaryotic Cells

Microorganisms are ubiquitous. They can be found in air, water, soil, inside and on the surfaces of plants, animals and humans. They live in a variety of habitats and under a wide variety of environmental conditions.  Microorganisms vary principally in their morphology and, depending on the degree of structural complexity are broadly classified as prokaryotes and eukaryotes.

Prokaryotes

The word “prokaryotes” also spelled “procaryotes” is coined from two Greek words pro, before, and karyon, nut or kernel. It is used to describe unicellular (single-celled) organisms that lack true nucleus and membrane-bound cell organelles. This means that the genetic material in prokaryotes is not bound within a nucleus.

Prokaryotes are divided into two domains, bacteria and archaea. Bacteria used to be considered as the only category of prokaryotic cells, but in 1990 a second group, the archaea, were recognized as having equal status to bacteria.

Archaea tend to live in harsh environmental conditions (such as high temperatures, extremes pH or salinity etc.) and often possess unusual modes of metabolism. All other organisms including humans have the eukaryotic structure with relatively more complex architecture.

Differences between prokaryotic and eukaryotic cells: Picture of prokaryotic cell

Prokaryotic cell (Source: www.courses.lumenlearning.com)

Prokaryotic cell structures and functions

Capsules and slime layers Resistance to phagocytosis, adherence to surfaces
Cell wall Gives bacteria shape and protection from lysis in dilute solutions
Endospore Survival under harsh environmental conditions
Fimbriae and pili Attachment to surfaces, bacterial mating
Flagella Provides the power of motility or self-propulsion
Gas vacuole Buoyancy for floating in aquatic environments.
Inclusion bodies Storage of carbon, phosphate, and other substances
Nucleoid Localization of genetic material (DNA)
Periplasmic space Contains hydrolytic enzymes and binding proteins for nutrient processing and uptake’
Plasma membrane Selectively permeable barrier, mechanical boundary of cell, nutrient and waste transport, location of many metabolic processes (respiration, photosynthesis), detection of environmental cues for chemotaxis
Ribosomes Protein synthesis

Read Also: Microorganisms of Pharmaceutical Interest

Eukaryotes

Eukaryotes (eucaryotes) are organisms made up of cells that possess a membrane-bound nucleus. Just like prokaryotes, the word “eukaryotes” is derived from two Greek words eu, true, and karyon, nut or kernel.

A typical eukaryotic cell is surrounded by a plasma membrane and contains many different structures and organelles with a variety of functions. The major groups of microorganisms (fungi, protozoa and algae), as well as parasitic worms and mites, and all plants and animals up to and including humans all belong to this group.

Viruses do not have a cellular structure and so some scientists do not even regard them as living but merely mixtures of complex chemicals; nevertheless, they are indisputably agents of infection and for that reason are usually considered as part of the microbial world.

Differences between prokaryotic and eukaryotic cells: Picture of Eukaryotic cell

Eukaryotic cell (Source: www.biologydictionary.net)

Eukaryotic cell structures and functions

Cell wall and pellicle Strengthen and give shape to the cell
Chloroplasts Photosynthesis—trapping light energy and formation of carbohydrate from CO2 and water
Cilia and flagella Cell movement
Cytoplasmic matrix Environment for other organelles, location of many metabolic processes
Endoplasmic reticulum Transport of materials, protein and lipid synthesis
Golgi apparatus Packaging and secretion of materials for  various purposes, lysosome formation
Lysosomes Intracellular digestion
Microfilaments, intermediate filaments, and microtubules Cell structure and movements, form the cytoskeleton
Mitochondria Energy production through use of the tricarboxylic acid cycle, electron transport, oxidative phosphorylation, and other pathways
Nucleolus Ribosomal RNA synthesis, ribosome construction
Nucleus Repository for genetic information, control centre for cell
Plasma membrane Mechanical cell boundary, selectively permeable barrier with transport systems, mediates cell-cell interactions and adhesion to surfaces, secretion
Ribosomes Protein synthesis
Vacuole Temporary storage and transport, digestion (food vacuoles), water balance (contractile vacuole)

Differences between Prokaryotic and Eukaryotic Cells

The various differences between prokaryotic and eukaryotic cells are listed in the table below.

Characteristic Prokaryote Eukaryote
Size Typically 1 – 5  µm Normally greater than 10  µm
Cell nucleus Do not possess a true nucleus Have a nucleus surrounded by a nuclear membrane
Location of chromosomes In the cytoplasm, usually attached to the cell membrane Within a true nucleus separated from the cytoplasm by a nuclear membrane
Nuclear division and reproduction Mitosis and meiosis are
absent so reproduction is asexual
Exhibit both mitosis and
meiosis, so reproduction may be sexual or asexual or both
depending on species
Nucleolus Absent Present
Genetic variation Resulting largely from mutations Resulting both from mutations and the creation of new gene combinations during sexual
reproduction
Mitochondria, chloroplasts and ribosomes Mitochondria and chloroplasts
absent; ribosome size is 70s
Mitochondria and chloroplasts may be present; ribosomes larger: 80s
Chemical composition Do not possess sterols in the cell membrane but do
usually have peptidoglycan in
the cell walls
Do possess sterols in the
cell membrane but no
peptidoglycan in the walls
Flagella Structurally simple Structurally complex
Pili Present Absent
Storage compounds Poly -β- hydroxybutyrate often present Poly -β- hydroxybutyrate absent

References

  • Denyer, S., Hodges, N., Gorman, S. and Gilmore, S. (2011). Hugo and Russell’s Pharmaceutical Microbiology. UK: Blackwell Publishing Ltd.
  • Ezeonu, I., Okafor, J. and Ogbonna, J. (2011). Laboratory Exercise in Microbiology: A Practical Manual for Students of Tertiary Institutions. Nigeria: Ephrata Printing and Publishing Company.
  • Hanlon, G. and Hodges, N. (2013). Essential Microbiology for Pharmacy and Pharmaceutical Science. UK: John Wiley & Sons, Ltd.
  • Okore, V. (2009). Principles of Pharmaceutical Microbiology (2nd ed.). Nigeria: Ephrata Publishers.

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