Prokaryotes and eukaryotes

Based on the cellular structures, cells are divided into prokaryotes and eukaryotes. They differ in many ways but the most predominant difference is their nuclear membrane, Eukaryotes have a distinct nuclear membrane within which the central nuclear organelles present whereas the prokaryotes don’t have a closed nuclear membrane. The living things are broadly categorized into 3 domains: Bacteria, Archaea and Eukarya. The single-celled organisms fall under the domain bacteria and archaea and they are generally known as the prokaryotes. The cells of the prokaryotic organisms are very primitive, small, not much evolved like we see in the eukaryotes. On the other hand, eukaryotic cells are complex, evolved, and have distinct organelle structures. They can be both unicellular and multicellular organisms that include animals, plants, fungi and protists. Furthermore, organisms such as yeasts and fungi belong to both the prokaryotic and eukaryotic domains because they share the characteristics of both eukaryotes and prokaryotes. This article provides information regarding the similarities and differences between the 2 domains in detail.

 

 

The general characteristics of eukaryotic cells
 

  1. Nucleus

Most of the eukaryotic cells contain a well-defined nucleus in which the  DNA is found. DNA helps in protein synthesis along with the ribosomes. Chromosomes are present inside the nucleus, which is surrounded by the nuclear envelope- a  bi-lipid layer regulating osmosis and diffusion.

  1. Cytoplasm

It is where other organelles are dispersed and it helps in various metabolic activities of the cell through its organelles such as mitochondria, chloroplasts, Golgi bodies, etc. also take place here. The cytoplasm contains Mitochondria that act as a powerhouse of the cell as it takes the responsibility of making ATP. Chloroplasts are found in algae and plants essential for converting the solar energy into chemical energy through photosynthesis. Golgi apparatus encompasses a stack of flattened, disc-shaped folds called that helps in the packaging of materials and also to secrete them. Lysosomes and Vacuoles are produced by the endoplasmic reticulum and Golgi apparatus which assist in the digestion of intracellular molecules in the presence of the enzyme called hydrolase. Cilia or Appendages along with flagella help in the movement of a cell if necessary. Cilia are shorter than flagella and numerous.

  1. Cell Wall

It provides shape, rigidity, and structural support to the cell. It is made up of cellulose, pectin, chitin or peptidoglycan but it may slightly differ between different organisms.

  1. Plasma Membrane

It is a thin semipermeable membrane around the cytoplasm. It acts as the barrier that regulates the entry and exit of the substances. It is also called the plasma membrane made up phospholipid bilayer embedded with proteins.

  1. Ribosomes:

 They help in protein synthesis. Eukaryotes contain 80S ribosomes which are again categorized into 2 subunits called 40S and 60S.

  1. Cytoskeleton

Cytoskeleton act as a supporting framework of the cells made up of 2 types of structures, microtubules and microfilaments. Microtubules are made up of a protein called tubulin which measures about 24nm. ON the other hand, microfilaments measure about 6nm, and are made of the protein called actin.

 

 

Characteristics of prokaryotic Cells

Pro means ‘old,’ and karyon stands for nucleus. They have a solid history of 3.5 billion years and used in different industries such as food, dairy, medicines etc.  They contain Glycocalyx –a layer that acts as a receptor. Nucleoid is the space furnished to accommodate the genetic material called DNA. Pilus is a hair-like hollow attachment found on the surface of bacteria, helping in transferring the DNA to other cells during cell-cell adhesion. Mesosomes are the extension of the cell membrane, unfolded into the cytoplasm and they assist in the cellular respiration. Flagellum is hair-like projections assist in the cellular movement.  Cell Wall provides rigidity and support for the cell. Fimbriae help in attaching the surface of the organism with other bacteria while mating. Granules help in the storage of carbohydrates, glycogen, phosphate, fats in the form of particles. The cell membrane is a thin layer made up of protein and lipids, surrounds cytoplasm and regulate the flow of materials inside and outside the cells.

 

 

Similarities between prokaryotes and eukaryotes

Even though prokaryotic and eukaryotic cells differ in lot many ways, they are alike in many interests. Some of the common features they both share includes the following:

  1. Both of them have DNA that determines the genetic code controlling all the bodily structure and functions.

  2. The outermost layer in both of them is the cell membranes that acts as a selectively permeable membrane through which materials enter and exit.

  3. Both the domains contain cytoplasm- a jelly-like substance composed primarily of water, salts and proteins.

  4. Ribosomes are responsible for protein synthesis in both the organisms.

  5. Vacuoles are found in both.

 

 

       Differences between prokaryotes and eukaryote

Feature


Eukaryotic Cell

Prokaryotic Cell

Nucleus

Present

Absent

Number of chromosomes

More than one

One--but not true chromosome: Plasmids

Cell Type

Usually multicellular

Mostly  unicellular  except some cyanobacteria

True Membrane bound Nucleus

Present

Absent

Example

Animals and Plants

All Bactria and archaea

Genetic Recombination

Occurs by meiosis and fusion of gametes

Partial, and many are asexual in their reproduction.

Lysosomes and peroxisomes

Present

Absent

Microtubules

Present

Absent or rare

Endoplasmic reticulum

Present

Absent

Mitochondria

Present

Absent

Cytoskeleton

Present

Usually  absent

DNA wrapping on the proteins.

Eukaryotes wrap their DNA around histones –a type of proteins.

A number of proteins act together to fold and condense the prokaryotic DNA. Folded DNA is again re-organized into a variety of conformations that are supercoiled and wound around tetramers of the HU protein.

Ribosomes

Appears larger

Looks smaller

Vesicles

Present

Present

Golgi apparatus

Present

Absent

Chloroplasts

Present in plant eukaryocytes

It is sometimes present but scattered in the cytoplasm

Flagella

They are microscopic in size and are membrane bound; usually arranged as 9 doublets surrounding 2 singlets

They are too small hence they are submicroscopic in size, composed of only 1 fiber

Permeability of the  Nuclear Membrane

Selectively permeable

Nuclear membrane is absent

Plasma membrane with steroid

It is present

Usually absent

Cell wall

Only in plant cells and fungi (chemically simpler)

Usually chemically complex

Cell size

Usually larger than prokaryotes and it measures between 10-100um

Smaller than eukaryotes, measures between  1-10um

 

 



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