Difference Between Prokaryotes and Eukaryotes: Prokaryotes and Eukaryotes are the two fundamental or basic classes of cells. They are mainly distinguished by their size and internal structures. The existence of two classes of cells without any intermediate type represents one of the most fundamental evolutionary separations in the living world. Prokaryotes are structurally and evolutionarily more primitive to eukaryotes. Even though they are two separate classes of living organisms, they share many common characteristics.
The shared properties reflect the fact that eukaryotic cells most certainly evolved from prokaryotic ancestors.
Shared common characters of prokaryotes and eukaryotes are as follows:
(1). Cellular contents in both prokaryotes and eukaryotes are limited by plasma membrane
(2). In both groups, plasma membrane composed of lipid bilayer with intermittent protein molecules
(3). DNA is the genetic information carrier in both the groups
(4). Chemical composition of nucleic acids (DNA and RNA), their structure and their organization are similar in both groups
(5). Even though the mechanism slightly varies, the process of transcription, translation and DNA replication occurs in both prokaryotes and eukaryotes
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(6). Both groups processes regulation of expression of genetic information
(7). mRNA acts as the intermediate molecule between genetic information and their expression (as proteins) in both groups
(8). Proteins are the expression of genetic information in both groups
(9). All the 20 protein coding amino acids are similar in prokaryotes and eukaryotes
(10). All the 61 codons are similar in both groups
(11). All the tree stop codons (UAA, UAG, UGA) are similar in both groups
(12). Structure of tRNA is similar in both groups
(13). Metabolic pathways such as glycolysis and TCA cycle are similar in both prokaryotes and eukaryotes
(14). In both groups, the metabolic pathways are multi-step processes each step catalyzed by specialized proteins called enzymes
(15). ATP is the energy currency in both prokaryotes and eukaryotes
(16). ATP is produced by the use of proton (H+) gradient, which is similar in both groups
(17). Photosynthesis is similar in both prokaryotes (blue green algae) and eukaryotes (plants)
(18). In both forms, photosynthesis consists of two process, light dependent ‘light reaction’ and light independent and ‘dark reaction’
(19). Proteasomes are with similar structure and working in both groups
Thus the overall biological process, events and organization are similar in both prokaryotes and eukaryotes. However each component and their interactions to each other vary in both groups.
The major differences between Prokaryotes and Eukaryotes are summarized in the following table:
.Sl. No. Prokaryotes Eukaryotes 1 ‘pro’ = pre, ‘karyon’= nucleus ‘eu’ = true, ‘karyo’ = nucleus 2 Originated about 3.5 billion years ago Originated about 1.2 billion years ago 3 Primitive forms Advanced forms 4 Usually unicellular organization Usually multicellular organization 5 Incipient nucleus, true nucleus absent True nucleus present 6 Small cell size, usually 1 – 10 µm Larger cell size, usually 5 – 100 µm, sometimes very large and macroscopic 7 Membrane bounded organelles such as nucleus, mitochondria, Golgi bodies, chloroplasts, lysosome, peroxisomes, ER etc. are absent Membrane bounded organelles present. Majority of organelles have single or double membrane system 8 Genetic material consists of single chromosome Genetic materials usually consists of more than one chromosomes 9 Genetic material is freely distributed in the central portion of the cell (nucleoplasm) Genetic material is located in the nucleus 10 Chromosome with covalently closed circular DNA (ccc DNA) Chromosome with linear DNA 11 Cell division by fission or budding, Mitosis and Meiosis completely absent Cell division by mitosis and meiosis 12 Nucleolus absent A well-developed nucleolus present 13 Ribosome 70S type Ribosome 80S type 14 Two subunits of ribosomes are 50S large subunit and 30S small subunit Two subunits of ribosome are 60S larger subunit and 40S smaller subunit 15 DNA is naked, not associated with histone proteins DNA is wrapped around histone proteins 16 Endoplasmic reticulum absent and hence protein synthesizing ribosome freely distributed in the cytoplasm Endoplasmic reticulum present, protein synthesizing ribosome usually attached to endoplasmic reticulum 17 Internal membrane system scarce. If present, associated with respiration and photosynthesis Internal membrane system well developed. Cell organelles are surrounded by single or double membranes 18 Flagella with simple organization Flagella (if present) is very complex with 9 + 2 arrangement of microtubules 19 Microtubules absent in flagella Microtubules present in flagella 20 Flagella extracellular and not enclosed by cell surface membrane Flagella intracellular and surrounded by cell surface membrane 21 Cell wall is composed of muco-polysaccharides Cell wall (if present) composed of cellulose (in plants) and chitin (in fungi). Cell wall absent in animal cells 22 Organisms haploid, contain only a single copy of genome Organisms usually diploid very rarely polyploids, contains two copies of genome, one from each parent 23 Plasmid (extra-chromosomal genetic materials) usually present Plasmids absent, however mitochondria and chloroplasts are autonomous with its own genetic materials 24 Cytoskeleton system absent Cytoskeleton system well developed 25 Sexual reproduction absent Sexual reproduction present 26 Processes like transformation conjugation and, transduction present for genetic material exchange All such processes completely absent, and genetic exchange occurs through sexual reproduction 27 Respiration is by mesosomes Respiration is by mitochondria 28 Chloroplasts and mitochondria absent Chloroplasts and mitochondria present, both are double membrane bounded and autonomous with its own genetic materials 29 Photosynthesis takes place in the membrane system of cytoplasm Photosynthesis takes place in chloroplast. Chloroplasts contains membrane stacks into lamella or stroma 30 Nitrogen fixing capacity is present in some forms Nitrogen fixing capacity is completely absent. None of the eukaryotic cells is known to processes nitrogen fixing ability both in plants and animals 31 Endocytosis and phagocytosis completely absent Endocytosis and phagocytosis is present in some animals cells 32 Cytoplasmic movement (cyclosis) absent Cyclosis present 33 Well-developed intracellular and extracellular communication system absent Communication system is well developed and advanced 34 Cell cycle duration about 20 – 60 minutes Highly varies, rapidly dividing cells the cell cycle is ~ 24 hours 35 Regulatory mechanisms of DNA relatively simple Regulatory mechanism highly complex 36 Transcription and translation are continuous process and occurs simultaneously in the cytoplasm They are separate processes, transcription occurs in the nucleus whereas translation occurs in the cytoplasm