types of cell

1. Topic :- “Structural Organization of Prokaryotic cell and
difference between Prokaryotic and Eukaryotic cell’’

2. Prokaryotic Cell Structure
 More simple than eukaryotic cells. Can perform all functions
necessary for life.
 Members of domain bacteria are microscopic, relatively simple,
prokaryotic organisms whose cells lack a nucleus. Bacteria are
usually single-celled organisms and most have cell walls made up of
peptidoglycan.
 Although most bacteria exhibit typical prokaryotic cell structure (i.e.
they lack a membrane-bound nucleus), a few members of the
unusual phylum Planctomycetes have their genetic material
surrounded by a membrane.
 Chemical composition of prokaryotic cell :
Water – 70 %
Polysaccharides – 5 %
Lipids – 6 %
Phospholipids – 4 %

3. Structural organization of Prokaryotes
 Cell wall
 Glycocalyx
I. Slime Layer
II. Capsule
 Plasma membrane
 Plastid
 Cytoplasm
 Cytoplasmic Particles
 Surface appendages
I. Flagella
II. Pilli ,Fimbriae
 Endospores

4. z
Fig 1. Prokaryotic cell Structure

5. Bacterial Cell Wall
 Provides rigidity, strength, and protection.
 More complex than eukaryote cell walls.
 Bacterial cells almost always are bounded by a chemically complex
cell wall.
 The cell wall protects bacteria against osmosis. The cell wall is
chemically composed of peptidoglycans Peptidoglycans are unique
to bacterial cells.
 In Gram-positive bacteria, peptidoglycans consist of a single 20 to
80 nm thick homogeneous layer lying outside the plasma membrane.
 In contrast, the Gram-negative bacterial cell wall consists of 2 to
7 nm thick peptidoglycan layer covered a 7 to 8 nm thick outer
membrane.

6.  Gram positive cell wall :
composition :
Peptidoglycan ,Lipid ,Teichoic acid : Teichoic acid is water soluble
polymer of glycerol present in gram positive bacteria
 Gram negative cell wall
composition :
 Peptidoglycan
 Outer membrane: Lipid, Protien.

7. • Outer membrane :
In addition to peptidoglycan cell wall, the Gram-negative
bacterium contains an additional membrane, the outer
membrane. The constituents of this layer are not completely
similar to the plasma membrane. It contains lipopolysaccharides,
lipoproteins, proteins and phospholipids.

8. Glycocalyx
 Glycocalyx is a thick, high-molecular-weight secretory
substance and is present in many bacteria external to the
cell wall.
 It is composed of polysaccharide, polypeptide, or both.
The glycocalyx may be thick or thin, rigid or flexible,
depending on their chemical nature.
 The terms capsule and slime layer are frequently used to
describe glycocalyx layers. The rigid layers are organized
in a tight matrix called a capsule. If the layer is more
easily deformed and loosely attached to the cell wall, is
called a slime layer.
 Most capsules consist of polysaccharides. However, the
capsules of some bacilli (Bacillus anthracis) consist of
polypeptides.

10. Plasma membrane
• The bacterial plasma membrane is a unit membrane composed
primarily of protein and phospholipid. Its structural and
chemical features are similar to eukaryotic plasma membrane.
• One major difference in chemical composition of plasma
membranes between eukaryotic and prokaryotic cells is that
eukaryotes have sterols in their membranes. Sterols are absent
from the plasma membranes of all bacteria except
Mycoplasma.
• Plasma membrane performs many functions, including
transport, and energy transduction. Mesosomes are present in
both Gram-positive and Gram-negative bacteria, although they
are generally more prominent in the Gram-positive bacteria.

11. Mesosomes

12. Cytoplasm
 For a prokaryotic cell, the term cytoplasm refers to the substance of the cell inside
the plasma membrane. Cytoplasm is about 80% water and contains primarily
proteins(20-30%), carbohydrates(40%), lipids(50%), inorganic ions, and many
low molecular weight compounds. It lacks unit membrane-bound organelles.
 The major structures present in the cytoplasm are ribosomes, The bacterial
cytoplasm contains 70S ribosomes. Bacterial 70S ribosomes differ from
eukaryotic 80S ribosomes .
 Bacterial cytoplasm also contains many organic and inorganic reserve deposits
(granules) known as inclusion bodies, that may be membrane-bound or
membrane less. These membranes vary in composition. Some are proteinaceous in
nature, whereas others contain lipid.
 Examples of inclusion bodies present in bacterial cytoplasm are glycogen,
carboxysomes, polyphosphate granules and others.
 70-80 % water in cytoplasm.

13. Plasmids
 Plasmids (term coined by J.Lederberg) are
autonomous self-replicating molecules of DNA that
are maintained as discrete, extrachromosomal genetic
elements in bacteria. It is a replicon (replicon is self-
replicating molecule of nucleic acid).
 Plasmids are mostly DNA molecules. RNA plasmids
(both single-stranded and double-stranded form) are
very rare and reported in few plants, fungi and even
animals. Bacterial plasmids are usually much
smaller than the bacterial chromosome, varying
from less than 5 kbp to more than several hundred
kbp, though plasmids as large as 2 Mbp also occur in
some bacteria.
 Most bacterial plasmids are circular, negatively
supercoiled, but linear plasmids have also been
reported in few genera such as Borrelia and
Streptomyces.

14. Cytoplasmic Particles
 Ribosomes are found in the cytoplasm.
 They are important in protein synthesis.
 Some substances are stored in cytoplasm.
 Such as starch, lipids, iron.

15. Surface appendages
 Bacteria may or may not possess surface appendages. Three
types of surface appendage can be recognize certain bacterial
species: the flagella, which are organs of locomotion, pili ,
meant for conjugation ,fimbriae, meant for attachment.
 Flagella occur in both Gram-positive and Gram-negative
bacteria. Structurally, bacterial flagella are long appendages
 Number and distribution of flagella: The number and
distribution of flagella on the bacterial surface are character
istic for a given species and hence are useful in identifying and
classifying bacteria. Based on number and patterns of
distribution of flagella, bacteria may be:

16.  Monotrichous (trichous means hair) have one flagellum.
 Amphitrichous (amphi means on both sides) One flagellum
attached at each end.
 Lophotrichous (lopho means tuft)Cluster of flagella at one end or
both ends.
 Peritrichous (peri means around) Flagella are spread fairly evenly
over the whole surface.

17. Pili and Fimbriae
 The term pili (singular: pilus) is used to describe the thin, hair
like appendages on the surface of bacteria. Pill occurs almost
exclusively on Gram-negative bacteria. Only a few Gram-
positive bacteria such as Corynebacterium .Pili are more rigid
in appearance than flagella. It plays an important role in the
process of conjugation (hence sometimes called sex pill).
 Fimbriae are filamentous cell appendages, present in both
Gram-negative and Gram-positive bacteria. They a composed
of helically arranged protein subunits. Fimbriae mediate cell
attachment to surface. It can occur at the poles of the bacterial
cell or can be evenly distributed over the entire surface of the
cell. They can number anywhere from a few to several
hundreds per cell.

18. Pilli Fimbriae
Present in Gram-negative bacteria Present in both bacteria
Required for bacterial conjugation Used for cell attachment to surface
Number 1 to 10 per cell Numbers up to several 100 per cell
Long filamentous structure Short filamentous structure

19. Spores (Endospores)
 Bacteria in the genera Bacillus and
Clostridium form an exceptionally heat
resistant and dehydrated structure capable
of surviving for long periods in an
unfavorable environment. This dormant
structure is called an endospore since it
develops within the cell.
 These structures are extraordinarily
resistant to environmental stresses such as
heat, ultraviolet radiation, gamma
radiation, chemical disinfectants.
 The endospore structure is very complex
and has many layers that are absent from
the vegetative cell.

20. Bacterial growth
 Bacterial growth is an orderly increase in the quantity
of cellular constituents (i.e. cell mass) and number.
 The increase in bacterial cell number occurs by cell
division which is known as binary fission.
 Binary fission begins when the DNA of the cell is
replicated. Each circular strand of DNA then attaches to
the plasma membrane. The cell elongates, causing the
two replicated DNA to separate. The plasma membrane
then grows inward and splits the cell into two daughter
cells through a process called cytokinesis.
 A few bacterial species reproduce by budding; they
form a small bud that enlarges until its size approaches
that of the parent cell, and then it separates.

21. Binary Fission

22. Feature Prokaryotic cells Eukaryotic cells
Membrane bound
nucleous
Absent Present
DNA complexed
with histone
Absent Present
Number of
chromosomes
One More than one
Mitosis and meiosis Absent Present
Sterol in plasma
membrane
Absent(Except Mycoplasma) Present
Ribosome 70 s 80s and 70s
Cell wall Present in most of prokaryotic
cell. In Eubacteria made up of
peptidoglycan.
Made up of cellulose
in plant and chitin in
fungi, absent in animal
cell.

23. Features Prokaryotic cell Eukaryotic cell
pilli and fimbriae Present absent
Ribosomes Smaller larger
examples Bacteria Plant and animals

24. Prokaryotic Cell Wall Compounds
Prokaryotic Cell Wall Compounds (pp.111-132)
David Corbett et al., (2010)
• A common feature of many bacteria is the expression of a
layer of extracellular polysaccharide usually organised into
a different structure termed the capsule.
• The expression of a capsule results in the coating of the
bacterium in high molecular weight polysaccharide
molecules that mediate interactions between the bacterial cell
and its immediate environment.
• The ubiquity of capsule expression across a diverse array of
bacterial genera suggests that capsule expression is
advantageous in a number of including infections of plants
and animals and maintenance in a broad range of
ecosystems.

25. Cell Membrane, Prokaryotic Encyclopedia of
Microbiology (pp.341-356)
M.H saier et al. (2009)
 Prokaryotic life forms provide far greater diversity at the
molecular level than that found in eukaryotes. This fact is
reflected by the structures and compositions of their
membranes.
 In addition to cytoplasmic membranes, shared by all living
cells, many prokaryotes possess protective outer
membranes that have compositions very different from
those of their inner membranes as well as from those of the
outer membranes of other organismal types.
 The outer membranes of Gram-negative bacteria differ from
those of high G+C Gram-positive bacteria and archaea with
respect to both their lipid and their protein constituents.

26. Reference
• Book : Life Sciences Fundamentals and
Practice 1
• Pranav Kumar and Usha Mina -2021

27. THANK YOU