Main Difference – Prokaryotes vs Eukaryotes
Prokaryotes and eukaryotes are the two organizational levels of living organisms on earth. The main difference between prokaryotes and eukaryotes is that prokaryotes do not have membrane-enclosed organelles whereas eukaryotes have membrane-enclosed organelles. The genetic material of prokaryotes can be found in a specific location of the cytoplasm, which is called nucleus. But in eukaryotes, DNA is organized into a membrane-enclosed organelle called nucleus. The other organelles in eukaryotes are mitochondria, chloroplast, endoplasmic reticulum, Golgi apparatus, and lysosomes. Prokaryotic organisms include bacteria and cyanobacteria. Eukaryotic organisms include animals, plants, fungi, algae, and protozoa.
Key Areas Covered
1. What are Prokaryotes
– Definition, Organization, Examples
2. What are Eukaryotes
– Definition, Organization, Examples
3. What are the Similarities Between Prokaryotes and Eukaryotes
– Outline of Common Features
4. What is the Difference Between Prokaryotes and Eukaryotes
– Comparison of Key Differences
Key Terms: Animals, Bacteria, DNA, Eukaryotes, Fungi, Membrane-Bound Organelles, Nucleus, Plants, Prokaryotes
What are Prokaryotes
Prokaryotes refer to the organisms that do not have a nucleus and membrane-bound organelles. All prokaryotes are unicellular organisms. Most prokaryotes are 0.2 to 2 µm in size. The cell membrane of prokaryotes encloses water-soluble proteins, DNA, and metabolites in the cytoplasm. Though prokaryotes do not contain compartments called organelles in the cytoplasm, they still process some microcompartments, which act as primitive organelles. Bacteria and cyanobacteria are the two types of prokaryotes.
Four types of shapes can be identified in bacteria: spherical-shaped (cocci), rod-shaped (bacilli), spiral-shaped (spirochaete) and comma-shaped (vibrio). The bacterial cell wall is made up of peptidoglycans. Cell wall provides protection to the cell, maintains the shape and prevents dehydration. Some bacteria possess an outermost layer called capsule which is sticky, helping the cell to attach to surfaces. Flagella, a wipe-like structure, help the movement of the cell. Fimbriae, which is a numerous hair-like structure, also helps the attachment. Some bacteria consist of a glycocalyx which covers the cell membrane surroundings. The structure of a prokaryotic cell is shown in figure 1.
Figure 1: Prokaryotic Bacteria Cell
Bacterial cytoplasm is a gel-like substance which dissolves a variety of organic molecules. They consist of a primitive cytoskeleton. Small 70S ribosomes are present for protein synthesis. Genomic DNA is found in a region called nucleoid in the cytoplasm. Bacteria consist of a single circular chromosome. Some DNA pieces can be found in the cytoplasm as circular plasmids.
Asexual reproduction of prokaryotes occurs via binary fission. The sexual reproduction method of prokaryotes is the horizontal gene transfer. Bacterial gene transfer occurs in three methods: transduction mediated by bacteriophages, conjugation mediated by plasmids, and natural transformation. Rod-like structures called pili allow the genetic transfer.
Since prokaryotes consist of great diversity, they obtain energy from inorganic compounds like hydrogen sulfide in addition to photosynthesis and organic compounds. They can also be alive in harsh conditions such as Antarctica snow surfaces, hot springs, and undersea hydrothermal vents. Eukaryotes are thought to be evolved from prokaryotes.
What are Eukaryotes
Eukaryotes are organisms that possess membrane-bound organelles including the nucleus. They can be either unicellular or multicellular organisms. Multicellular higher eukaryotes contain specialized tissues made from different types of cells. Eukaryotes can be identified in four kingdoms: kingdom Protista, kingdom Plantae, kingdom Fungi, and kingdom Animalia.
Eukaryotic cells are large in size (10 to 100 µm) when compared to prokaryotes. The three main types of prokaryotic cells are animal cells, plant cells, and fungal cells. Plants and fungi possess a cell wall made up of cellulose, hemicellulose, pectin, and chitin respectively. Eukaryotic cytoskeleton is composed of microfilaments, microtubules, and intermediate filaments. It plays a vital role in the cellular organization and maintaining the shape of the cell. Eukaryotes and prokaryotes are described in video 1.
Video 1: Eukaryotes and Prokaryotes
Eukaryotic cells are composed of a variety of membrane-bound organelles. The nucleus is enclosed by two membranes called nuclear membranes. Eukaryotes usually contain more than one chromosomes in the nucleus. These chromosomes are linear and often exist in multiple copies called homologous. Nuclear membranes develop the endoplasmic reticulum (ER) which is involved in protein maturation and transportation. Ribosomes are large, 80S in size and are bound to the ER. Ribosome-bound ER is referred to as rough ER. Vesicles are present for the transformation of various molecules within the cell such as Golgi bodies, lysosomes, and peroxisomes. Mitochondria are also surrounded by two phospholipid bilayers. They covert sugar into ATPs to utilize as energy. Plant cells contain chloroplasts for photosynthesis. Eukaryotes reproduce either asexually through mitosis or sexually through meiosis followed by the fusion of gametes.
Similarities Between Prokaryotes and Eukaryotes
- Both prokaryotes and eukaryotes are two types of organization of life.
- Both prokaryotes and eukaryotes contain a cell membrane, which is made up of a phospholipid bilayer.
- The genetic material of both prokaryotes and eukaryotes is DNA.
- Both prokaryotes and eukaryotes contain ribosomes, which facilitates the translation of mRNA into an amino acid sequence.
- Both prokaryotes and eukaryotes are composed of a cytosol.
Difference Between Prokaryotes and Eukaryotes
Definition
Prokaryotes: Prokaryotes are organisms that do not possess a nucleus and membrane-bound organelles.
Eukaryotes: Eukaryotes are organisms that possess membrane-bound organelles including the nucleus.
Kingdom
Prokaryotes: Prokaryotes belong to the kingdom Monera.
Eukaryotes: Eukaryotes belong to kingdom Protista, kingdom Plantae, kingdom Fungi, and kingdom Animalia.
Examples
Prokaryotes: Bacteria and cyanobacteria are prokaryotic cells.
Eukaryotes: Animals, plants, fungi, protozoa, and algae are eukaryotes.
Size of the cell
Prokaryotes: Prokaryotic cells are normally 0.2 to 2 µm in diameter.
Eukaryotes: These cells are normally 10 to 100 µm in diameter.
Cell Type
Prokaryotes: Prokaryotes are unicellular organisms.
Eukaryotes: Eukaryotes are multicellular organisms.
Nucleus
Prokaryotes: Prokaryotes have no true nucleus, no nuclear membranes or nucleoli.
Eukaryotes: Eukaryotic cells consist of a true nucleus with double nuclear membranes and nucleoli.
DNA
Prokaryotes: Prokaryotes have a single, circular DNA molecule in the nucleoid, They lack histones or exons.
Eukaryotes: Eukaryotic cells have multiple, linear chromosomes in the nucleus. They contain Histones, and exons.
Membrane-bound Organelles
Prokaryotes: Prokaryotes cells lack membrane-bound organelles.
Eukaryotes: Membrane-bound organelles such as mitochondria, chloroplast, ER, and vesicles are present in eukaryotes.
Flagella
Prokaryotes: Flagella are made up of two proteins in prokaryotes.
Eukaryotes: Some eukaryotic cells without a cell wall contain flagella.
Cell Wall
Prokaryotes: Prokaryotic cell walls are mostly made up of peptidoglycans.
Eukaryotes: Eukaryotic cell walls are made up of cellulose, chitin, and pectin.
Plasma Membrane
Prokaryotes: Carbohydrates and sterols are not found in the plasma membrane of prokaryotes.
Eukaryotes: Carbohydrates and sterols serve as receptors on the plasma membrane of eukaryotes.
Cytoskeleton
Prokaryotes: Prokaryotes contain a primitive cytoskeleton without cytoplasmic streaming.
Eukaryotes: Eukaryotes contain a complex cytoskeleton with cytoplasmic streaming.
Cell Division
Prokaryotes: Cell division occurs through binary fission in prokaryotes.
Eukaryotes: Cell division takes place through mitosis in eukaryotes.
Sexual Reproduction
Prokaryotes: Sexual reproduction of prokaryotes occurs by conjugation.
Eukaryotes: Sexual reproduction occurs through production of gametes in eukaryotes
Conclusion
Prokaryotes and eukaryotes are two types of organisms on earth. Bacteria and cyanobacteria are prokaryotes. Animals, plants, fungi, protozoa, algae, are eukaryotes. Prokaryotes do not contain membrane-bound organelles and a nucleus. But, eukaryotes contain membrane-bound organelles and a nucleus. The main difference between prokaryotes and eukaryotes is their cellular organization.
Reference:
1. “Prokaryote.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 27 Aug. 2014, Available here.
2.“Intro to eukaryotic cells.” Khan Academy, Available here.
Media Courtesy:
1. “Prokaryote cell” By Ali Zifan – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Prokaryotes vs. Eukaryotes” by eLearn.Punjab via Vimeo.com
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