Prokaryotes are unicellular organisms that lack internal membrane-bound structures. They are divided into bacteria and archaea. Prokaryotic cells lack a nucleus but contain a nucleoid region where DNA is located. Archaeal membranes contain isoprene lipids instead of fatty acids found in bacteria. Prokaryotes reproduce through binary fission and exchange genetic material through transformation, transduction, and conjugation.

1. Prokaryotes
• Prokaryotes are unicellular organisms that lack organelles or other internal
membrane-bound structures
• They are found in both domains – Bacteria and Archaea
• Key points :-
• Prokaryotic cells lack a defined nucleus, but have a region in the cell, termed the
nucleoid, in which a single chromosomal, circular, double-stranded DNA molecule is
located.
• Archaeal membranes have replaced the fatty acids of bacterial membranes with
isoprene; some archaeal membranes are monolayer rather than bilayer.

2. 
• Key terms :-
• nucleoid: the irregularly-shaped region within a prokaryote cell
where the genetic material is localized
• plasmid: a circle of double-stranded DNA that is separate from
the chromosomes, which is found in bacteria and protozoa
• osmotic pressure: the hydrostatic pressure exerted by a solution
across a semipermeable membrane from a pure solvent
• The Plasma Membrane :-
• In archaeal cell membranes, isoprene (phytanyl) chains linked to
glycerol replace the fatty acids linked to glycerol in bacterial
membranes.
• Some archaeal membranes are lipid monolayers instead of
bilayers.

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4. 
• Archaeal phospholipids differ from those found in Bacteria and
Eukarya in two ways.
• First, they have branched phytanyl(isoperene) sidechains
instead of linear ones.
• Second, an ether bond instead of an ester bond connects the
lipid to the glycerol.
• The compound ester possesses a carbon-carbonyl-oxygen bond,
while the ether compound has a carbon-oxygen-carbon bond.

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6. 
• The P.M. also provide specific site at which the single DNA
remain attached. It is the point from where DNA replication
start.

7. P.M. Intrusion
• Infolding of the p.m. of all gram + and gram – bacteria give rise
two main types of structures :
• Mesosomes ( chondriods) :- an organelle of bacteria that
appears as an invagination of the plasma membrane and
functions either in DNA replication and cell division or excretion
of exoenzymes
• They are seen in Nitrosomonas(chemoautotrophic) and
Rhodopseudomonas (photosynthetic pigment) bacteria.

8. 
• Mesosome are also involved in cross-wall (septum)
formation during the division of cell.
• Chromatophores :-
• these are photosynthetic pigment-bearing membranous
structure of photosynthetic bacteria.
• they vary in form as vesicles, tubes, bundled tubes, stacks
or thylakoid ( as in cynobacteria)
• Rhodospirillum rubrum

9. 
• Cell wall :-
• The cytoplasm of prokaryotic cells has a high concentration of
dissolved solutes. Therefore, the osmotic pressure within the
cell is relatively high. The cell wall is a protective layer that
surrounds some cells and gives them shape and rigidity.
• The cell wall is absent in Mycoplasma
• Bacterial cell walls contain peptidoglycan composed of
polysaccharide chains that are cross-linked by unusual peptides
containing both L- and D-amino acids, including D-glutamic acid
and D-alanine.
• Proteins normally have only L-amino acids; as a consequence,
many of our antibiotics work by mimicking D-amino acids and,
therefore, have specific effects on bacterial cell wall
development.

10. 
• Peptidoglycan layer contain carbohydrates and proteins
• Bacteria are divided into two major groups: gram-positive and
gram-negative, based on their reaction to gram staining.
• Note that all gram-positive bacteria belong to one phylum
• bacteria in the other phyla (Proteobacteria, Chlamydias,
Spirochetes, Cyanobacteria, and others) are gram-negative.
• Gram-positive bacteria can be divided into two major
subdivisions:
• the phylum Actinobacteria, also described as the high-G+C
gram-positives.
• the phylum Firmicutes, also known as the low-G+C gram-
positives, a group that includes such well-known genera
as Bacillus and Clostridium.

11. 
• Gram-positive bacteria typically have a cell wall consisting of a
single thick layer of peptidoglycan.
• the most thoroughly studied gram-positive bacteria include
human pathogens (e.g., Mycobacterium tuberculosis, Bacillus
anthracis)
• Gram postive cell wall consist of : peptidoglycan and teichoic acid
• Peptidoglycan is complex of oligosaccharide and short peptide
• Oligosaccharide are N-acetylglucosamine & N-acetylmuramic acid
• Teichoic acid are coploymer of glycerol phosphate or ribitol
phosphate and carbohydrate linked via phosphodiester bond
• They are covalently linked to N-acetylmuramic acid or a terminal
D-alanine in the tetrapeptide
• The main function of teichoic acids is to provide rigidity to the cell-
wall by attracting cations such as magnesium and sodium.

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13. 
• Teichoic acids may be covalently linked to lipids in the plasma
membrane to form lipoteichoic acids.
• Lipoteichoic acids anchor the cell wall to the cell membrane.

14. 
• Gram negative :- Escherichia coli
• Cell wall consist of three layers Peptidoglycan, Periplasmic space,
Outer membrane
• Peptidoglycan layer is thin lacks teichoic acid and lies next to
P.M.
• The periplasmic space lies outside the peptidoglycan layer and
contains proteins secreted by cell
• The outer layer consists of lipid bilayer and contains
lipopolysaccharide
• It is permeable and also contain proteins called porin which lines
channels large enough to let many chemicals pass

15. 
• Peptidoglycan are chemically similar in all prokaryotes and
differ only in the types of AA present in peptide portion of
molecule

16. 
characteristics Gram positive Gram negative Blue green algae
Layers 1 3 3
peptidoglycan + (thick) + (thin) + (thin)
Teichoic acid + - -
lipopolysaccharide - + +
Gram stain + - +

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18. 
• Capsule :- in some bacteria, the cell wall is surrounded by an
additional slime or gel layer called capsule.
• It is thick, gummy, mucilaginous and is secreted by the P.M.
• The capsule serves mainly as a protective layer against attack by
phagocytes and by viruses
• It also help regulating the concentration and uptake of essential
ions and water.
• Capsule (also known as K antigen) is a major virulence factor of
bacteria, e.g. all of the principal pathogens which cause
pneumonia and meningitis, including Streptococcus
pneumoniae, Haemophilus influenzae, Neisseria meningitidis,
Klebsiella pneumoniae, Escherichia coli, and group B
streptococci have polysaccharide capsules on their surface

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20. Forms of Bacteria
• Cocci:- these bacteria are spherical or round in shape
• E.g. Diplococcus pneumonia(diplococci), streptococus
pyrogenes(bead like chain, cause sore throat)

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• Bacilli :- rod like bacteria
• Bacillus cause certain disease of man like
• Tuberculosis – mycobacterium or bacillus tuberculosis
• Tetanus – clostridium tetani, Typhoid – salmonella typhous
• Diptheria – corynebacterium diptheriae,
• Leprosy – mycobacterium leprae
• Dysentery or food poisoning – closteridium botylinum
• Anthrax – bacillus anthracis

22. 
• Spirilla :- these are also called spirochetes
• these are spiral shaped and motile bacteria
• Spirilla cause human disease such as syphilis(treponema
pallidium)
• Vibrio :- these are comma-shaped or bent-rod like bacteria
• Cause cholera – vibrio cholerae

23. Flagella
• Flagella for cellular locomotion
• Consist of single type of protein - flagellin

24. 
• The flagellum is attached at its base, by a short flexible hook
that is rotated like a propeller of ship, By the flagellar rotatory
motor
• The flagellar motor comprises four distinct parts :-
• The Rotor(M ring), Stator, Bearing ( S ring ) and Rod
• The Rotor is a protein disc integrated into the P.M.
• Rotor is driven by energy stored in the trans-membrane proton
H+ gradient & rotate rapidly in the lipid bilayer against another
protein disc called Stator
• A rod links the rotor to a hook & flagellum, thereby causing
them to rotate
• The protein Bearing serves as a seal the outer membrane of the
cell wall as the rotating rod passes through it
• The stator & bearing remains stationary

25. 
• The shaft bears a pair of ring in Gram + and two pairs of ring in
Gram negative
• The bacterial flagellum usually does not have any bounding
membranes and it grows at the tip
• Eukaryotic flagellum grows at the base adjacent to the basal
body

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27. 
• Fimbriae or pili :- are non-motile but adhesive structure
• they enable the bacteria to stick firmly to other cells, to a
surface
• Pili help in conjugation ( sex pili)
• E.g. Gonorrhea- causing coccus, Neiseria gonorrhoeae

28. Transfer of Genetic Material in Bacterial Cells
• It take place in three ways :-
1) Transformation:-Bacterial transformation is a process of
horizontal gene transfer by which some bacteria take up
foreign genetic material (naked DNA) from the environment.
* It was first reported in Streptococcus pneumoniae by Griffith
in 1928.
* DNA as the transforming principle was demonstrated by Avery
et al in 1944.

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30. 
• Transduction :-a process of genetic recombination in bacteria
in which genes from a host cell (a bacteria) are incorporated into
the genome of a bacterial viruse (bacteriophage) and then carried
to another host cell when the bacteriophage initiates another
cycle of infection.

31. 
• Conjugation :- is the process by which one bacterium transfers genetic
material to another through direct contact.
• During conjugation, one bacterium serves as the donor of the genetic material,
and the other serves as the recipient.
• The donor bacterium carries a DNA sequence called the fertility factor, or F-
factor.
• The F-factor allows the donor to produce a thin, tubelike structure called a
pilus, which the donor uses to contact the recipient.
• The pilus then draws the two bacteria together, at which time the donor
bacterium transfers genetic material to the recipient bacterium.

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Thanks
Sukhmeet Kang