The document provides an overview of prokaryotic and eukaryotic cells, including their definitions, structures, and key differences. Prokaryotes are unicellular organisms without a nucleus, while eukaryotes are more complex and contain membrane-bound organelles, including a nucleus. The text emphasizes the importance of understanding these cellular distinctions for studying genetics and microbiology.

1. Prokaryotes and Eukaryotes
Md. Atick Chowdhury
Faculty of Fisheries,
Sylhet Agricultural University, Sylhet-3100,
Bangladesh.
E-mail: atickturja@gmail.com

2. 2
CONTENTS
Topics Pages
01. Introduction 03
02. Prokaryotes 04
03. Prokaryotic Cell 05
04. Eukaryotes 05
05. Eukaryotic Cell 07
06. Comparison between Prokaryotic and Eukaryotic Cell 08
07. Conclusion 09
08. References 09

3. 3
01. Introduction:
The smallest unit of life is cell. All living beings except the viruses are composed of one or many
cells. On the cytological basis, the cellular organisms fundamentally may have either
prokaryotic cells or eukaryotic cells.
The cell can be defined as a basic functional unit of life. The term cell is derived from the Latin
word and was first observed by a scientist named Robert Hook in the year 1665. All living
organisms are composed of one or many cells to perform their individual functions. A cell is a
smallest unit of a life, which is able to control and perform several functions in all living
organisms. All unicellular organisms (single cell) including bacteria and archae, which are
composed of a single cell, are examples of prokaryotic cells. All multicellular organisms (many
or more than one cell) including humans, which are composed of complex or many cells, are
examples of eukaryotic cells. Both prokaryotic cells and eukaryotic cells have cytoplasm, cell
membrane and genetic material in common.

4. 4
02. Prokaryotes:
Greek word ‘pro’ means before and ‘karyon’ means nut or kernel, referring to the cell nucleus.
Prokaryotes are organisms without a cell nucleus, or any other membrane bound organelles.
Most prokaryotes are unicellular, but some prokaryotes are multicellular.
Examples: Blue-green algae (cyanobacteria), bacteria, archaea etc.
Figure: Micrscopic view of Prokaryote (Bacteria)
Bacteria (E.coli) Bacterial Colony
Cyanobacteria Archaea
Figure: Some Prokaryotes

5. 5
03. Prokaryotic Cell:
The cell which are composed of primitively organized cytoplasm and nucleus; the nuclear
substances (i.e. DNA and RNA) do not remain isolated or separated from the cytoplasm which
lacks in mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, centrioles etc., by any
nuclear membrane, are called prokaryotic cells.
The simplest types of cells are prokaryotic cells. Bacteria, the oldest form of life on Earth, are
prokaryotes. The DNA of prokaryotic cells is not contained within a nucleus. Instead,
prokaryotic chromosomes are found in a localized area of the cell called the nucleoid region.
Examples: The prokaryotic cells in blue-green algae and bacteria.
04. Eukaryotes:
Greek word ‘eu’ means good or true and ‘karyon’ means nut or kernel reffering to the cell
nucleus.
Eukaryotes are organisms whose cells are organized into complex structures by internal
membranes and cytoskeleton. The most characteristic membrane bound structure is the nucleus.
This feature gives them the name.
Examples: Animals, plants, fungi and protists etc.
Figure: Typical Prokaryotic Cell

6. 6
Figure: Microscopic View of Eukaryote (Animal cell)
Tenualosa ilisha
Homo sapiens
Macaca fascicularis
Oryza sativa
Nymphaea rubra
Ailuropoda melanoleuca
Figure: Some Eukaryotes

7. 7
05. Eukaryotic Cell:
According to Encyclopædia Britannica, “Eukaryote, any cell or organism that possesses a
clearly defined nucleus. The eukaryotic cell has a nuclear membrane that surrounds the nucleus,
in which the well-defined chromosomes (bodies containing the hereditary material) are located.
Eukaryotic cells also contain organelles, including mitochondria (cellular energy exchangers), a
Golgi apparatus (secretory device), an endoplasmic reticulum (a canal-like system of membranes
within the cell), and lysosomes (digestive apparatus within many cell types).”
From Wikipedia, the free encyclopedia, “A eukaryote is any organism whose cells contain
nucleus and other organelles enclosed within membranes.”
The eukaryotic cells have a true nucleus, i.e. the nuclear substances such as DNA containing
stainable and thread like chromosomes, RNA rich nucleolus and nucleoplasm, all remain well
separated from the cytoplasm by two perforated lipo-proteinous nuclear membrane.
A typical eukaryotic cell is composed of an outer plasma membrane, cytoplasm and nucleus.
Examples: Eukaryotic cells occur in most plants (from algae to angiosperms) and animals (from
protozoa to mammals).
Figure: Highly Schematic Diagram of a Composite Eukaryotic Cell, Half Plant and Half Animal

8. 8
06. Comparison between Prokaryotic and Eukaryotic Cell:
The distinction between prokaryotes and eukaryotes is considered to be the most important
distinction among groups of organisms. Eukaryotic cells contain membrane-bound organelles,
such as the nucleus, while prokaryotic cells do not. Differences in cellular structure of
prokaryotes and eukaryotes include the presence of mitochondria and chloroplasts, the cell wall,
and the structure of chromosomal DNA. Prokaryotes were the only form of life on Earth for
millions of years until more complicated eukaryotic cells came into being through the process of
evolution.
Table: Comparison between Prokaryotic and Eukaryotic Cell
Criteria Prokaryotic Cell Eukaryotic Cell
01. Nucleus Absent Present
02. Number of
chromosomes
One, but not true chromosome:
Plasmids
More than one
03. Cell Type Usually unicellular (some
cyanobacteria may be multicellular)
Usually multicellular
04. True Membrane
bound Nucleus
Absent Present
05. Genetic
Recombination
Partial, undirectional transfers DNA Meiosis and fusion of gametes
06. Lysosomes and
peroxisomes
Absent Present
07. Microtubules Absent or rare Present
08. Endoplasmic
reticulum
Absent Present
09. Mitochondria Absent Present
10. Cytoskeleton May be absent Present
11. DNA wrapping
on proteins
Multiple proteins act together to fold
and condense prokaryotic DNA.
Folded DNA is then organized into a
variety of conformations that are
supercoiled and wound around
tetramers of the HU protein.
Eukaryotes wrap their DNA around
proteins called histones.
12. Ribosomes Smaller Larger
13. Vesicles Present Present
14. Golgi apparatus Absent Present
15. Chloroplasts Absent; chlorophyll scattered in the
cytoplasm
Present (in plants)
16. Flagella Submicroscopic in size, composed of
only one fiber
Microscopic in size; membrane bound;
usually arranged as nine doublets
surrounding two singlets
17. Permeability of
Nuclear Membrane
Not present Selective
18. Plasma membrane
with steroid
Usually no Yes

9. 9
19. Cell wall Usually chemically complexed Only in plant cells and fungi
(chemically simpler)
20. Vacuoles Present Present
21. Cell size 1-10μm 10-100μm
22. Example Bacteria and Archaea Animals and Plants
07. Conclusion:
For cellular study in genetics the knowledge about prokaryotic and eukaryotic cell must be
studied clearly. Microorganisms and all other living organisms are classified as prokaryotes or
eukaryotes. Prokaryotes and eukaryotes are distinguished on the basis of their cellular
characteristics. For example, prokaryotic cells lack a nucleus and other membrane‐bound
structures known as organelles, while eukaryotic cells have both a nucleus and organelles.
Prokaryotic and eukaryotic cells are similar in several ways. Both types of cells are enclosed by
cell membranes (plasma membranes), and both use DNA for their genetic information.
Prokaryotes include several kinds of microorganisms, such as bacteria and cyanobacteria.
Eukaryotes include such microorganisms as fungi, protozoa, and simple algae. Viruses are
considered neither prokaryotes nor eukaryotes because they lack the characteristics of living
things, except the ability to replicate (which they accomplish only in living cells).
08. References:
i. Genetics, P.S. Verma & V.K. Agarwal
ii. Carp Genetic Resources, M.G. Hussain and M.A. Mazid, WorldFish Center
iii. Encyclopædia Britannica
iv. Wikipedia, the free encyclopedia