Eukaryote and prokaryote

 Cells are the structural and functional unit of life. Based on the structure and functions, cells are broadly classified as Prokaryotic and Eukaryotic. Prokaryotic Cells are considered to be the most primitive kind of cells and lack few features as compared to the eukaryotic cell. Eukaryotic cells have evolved from prokaryotic cells but contain different types of organelles like Endoplasmic reticulum, Golgi body, Mitochondria etc, which are specific in their functions. Thus, Prokaryotes are simple, small cells, whereas eukaryotic cells are complex, large structured. Prokaryotic cells do not have a well-defined nucleus but DNA molecule is located in the cell, termed as nucleoid, whereas eukaryotic cells have a well-defined nucleus, where genetic material is stored. 

Prokaryotes

The term “prokaryote” is derived from the Greek word “pro“, (meaning: before) and “karyon” (meaning: kernel). It translates to “before nuclei“. Prokaryotes are one of the most ancient groups of living organisms on earth, with fossil records dating back to almost 3.5 billion years ago. Prokaryotes thrived in the earth’s ancient environment, some using up chemical energy and others using the sun’s energy. These extremophiles thrived for millions of years, evolving and adapting.

Prokaryotic cells are comparatively smaller and much simpler than eukaryotic cells. Prokaryotic cells do not possess membrane-bound cell organelles such as a nucleus. Reproduction happens through the process of binary fission.

Structurally, prokaryotes have a capsule enveloping its entire body, and it functions as a protective coat, especially for preventing phagocytosis. The pilus is a hair-like appendage found on the external surface of most prokaryotes, commonly observed in bacteria. It helps the organism to attach itself to various environments. The pilus is also called attachment pili since it helps the organism resist from being flushed. The cell is bounded by a cell wall, which provides strength and rigidity to the cell. Inside lies the cytoplasm, contained within the plasma membrane, which separates the interior contents of the cell from the outside environment. Within the cytoplasm, ribosomes exist and it plays an important role in protein synthesis. Some prokaryotic cells contain special structures called mesosomes which assist in cellular respiration. Most prokaryotes also contain plasmids, which contains small, circular pieces of DNA. Flagella are present as locomotory organs. Pilus can also help in locomotion.  Common examples of Prokaryotic organisms are Eubacteria and Archaeabacteria (kingdom Monera.)

Eukaryotic Cell

The term “Eukaryotes” is derived from the Greek word “eu“, (meaning: good) and “karyon” (meaning: kernel), translating to “good or true nuclei.” Eukaryotes are more complex and much larger than the prokaryotes.  They include almost all the major kingdoms except kingdom Monera (Archae and Eu bacteria).

Structurally, some eukaryotes (plant cells) possess a cell wall, which supports and protects the plasma membrane. The cell is surrounded by the plasma membrane and it controls the entry and exit of certain substances. The nucleus contains DNA, which is responsible for storing all genetic information. The nucleus is surrounded by the nuclear membrane. Within the nucleus exists the nucleolus, and it plays a crucial role in synthesising proteins. Eukaryotic cells also contain mitochondria, which are responsible for the creation of energy, which is then utilized by the cell. Plant cells contain chloroplasts which are the sites of photosynthesis. Endoplasmic reticulum helps in the transportation of materials. Besides these, there are also other cell organelles that perform various other functions and these include ribosomes, lysosomes, Golgi bodies, cytoplasm, chromosomes, vacuoles and centrosomes.

Examples of eukaryotes include almost every unicellular organism with a nucleus and all multicellular organisms.

These two classes of cells are quite different. They both possess cell membrane and ribosomes. The general differences between the two types of cells are as follows:

Basis For Comparison	Prokaryotic Cells	Eukaryotic Cells
Size	0.5-3um	2-100um
Kind of Cell	Single-cell	Multicellular
Cell Wall	Cell wall present, comprise of peptidoglycan.	Usually cell wall absent, if present (plant cells and fungus), comprises of cellulose (polysaccharide). Animal cells have a cell membrane
Presence of Nucleus	No well-defined nucleus - 'nucleoid' is present containing DNA.	A well-defined nucleus is present enclosed within nuclear membrane.
Shape of DNA	Circular, double-stranded DNA.	Linear, double-stranded DNA.
Mitochondria	Absent	Present
Ribosome	70S	80S
Golgi Apparatus	Absent	Present
Endoplasmic Reticulum	Absent	Present
Mode of Reproduction	Asexual	Most commonly sexual
Cell Divison	Binary Fission (conjugation, transformation, transduction)	Mitosis ( for growth and healing), Meiosis (to produce eggs and sperm)
Lysosomes and Peroxisomes	Absent	Present
Chloroplast	(Absent) scattered in the cytoplasm.	Present in plants, algae.
Transcription and Translation	Occurs together.	Transcription occurs in nucleus and translation in cytosol.
Organelles	Organelles are not membrane bound, if present.	Organelles are membrane bound and are specific in function.
Replication	Single origin of replication.	Multiple origins of replication.
Number of Chromosomes	Only one (not true called as a plasmid).	More than one.
Examples	Archaea, Bacteria.	Plants and Animals.

 

The cell is the basic unit of life, responsible for all biological activities of the living being whether its prokaryote or eukaryote. The cell was first discovered in the year 1665 by Robert Hooke. The Cell Theory was explained by Theodor Schwann and Matthias Jakob Schleiden in the year 1830.