The document provides an overview of bacterial cell structure, including key components such as the nucleoid, cytoplasm, ribosomes, plasmids, cytoplasmic membrane, and cell wall. It discusses the morphology of bacteria, describing their shapes, differences between gram-positive and gram-negative bacteria, and functions of various structures like pili and flagella. Additionally, it highlights the medical significance of these features, such as antibiotic resistance and virulence factors.

1. Bacterial cell structure
and functions
Dr. Rabia Sadaf
Assistant Professor
Pathology

2.  My students will be able to identify shapes of
bacteria.
 They can describe different parts of bacterial cell and
their functions.
 They can also understand the differences between
gram positive and gram negative bacterial cell wall.
Learning Objectives

3.  Bacteria have characteristic shapes .
 Can be classified into these basic groups:
 Cocci (spherical)
 Bacilli (rod shaped)
 Spirochetes (spiral)
 Vibrio (coma shaped)
Morphology of Bacteria

4. Morphology of Bacteria

5. Morphology of Bacteria
 Different sizes of bacilli

6. Morphology of Bacteria

8. Bacterial cell structure

9. Bacterial structure

10.  Nucleoid:
 The bacterial nucleoid contains a single double-
stranded deoxyribonucleic acid (DNA)
 Only containing a single chromosome. Having no
nuclear membrane. Having no nucleolus.
 Replicating by growth and simple fission, and not by
mitosis.
Bacterial structure

11.  Cytoplasm: The cytoplasm of bacterial cell is a viscous
watery solution, or soft gel, containing a variety of
organic and inorganic solutes, and numerous
ribosomes.
 Inclusion granules are observed in the cytoplasm in
many species of bacteria.
 Containing plasmids in some species of bacteria. Not
containing endoplasmic reticulum and mitochondria.
Bacterial structure(contd..)

12.  Bacterial ribosomes:
 They are the site of protein synthesis as in eukaryotic
cells, but they differ from eukaryotic ribosomes in size
and chemical composition.
 Bacterial ribosomes are 70S in size, with 50S and 30S
subunits.
Bacterial structure(contd..)

13. Bacterial structure(contd..)
 Plasmids: They are
extrachromosomal,
double-stranded, circular
DNA molecules that are
capable of replicating
independently of the
bacterial chromosome.
 Two types, Transmissible
Non Transmissible

14. Functions of plasmids : Plasmids carry the genes for the
following functions and structures of medical importance.
 Antibiotic resistance
 Resistance to heavy metals, such as mercury and silver
 Resistance to ultraviolet light, which is mediated by DNA
repair enzymes.
 Pili (fimbriae)
 Exotoxins, including several enterotoxins
Bacterial structure(contd..)

15. Bacterial structure(contd..)
 Cytoplasmic membrane:
Just inside the cell wall
lies the cytoplasmic
membrane, which is
composed of a
phospholipid bilayer
similar in microscopic
appearance to that in
eukaryotic cells.

16.  Functions of cell membrane:
 Active transport of molecules into the cell
 Energy generation by oxidative phosphorylation
 Synthesis of precursors of the cell wall
 Secretion of enzymes and toxins
Bacterial structure(contd..)

17.  Cell wall : The cell wall is the layer, usually fairly rigid, that
lies just outside the cell membrane.
 It gives shape to the cell and protect it from osmotic lysis.
 The cell walls of many pathogens have components that
contribute to their pathogenicity .
 The wall can protect a cell from toxic substances and is the
site of action of several antibiotics.
 Peptidoglycan is the most important molecule in the cell
walls of bacteria
Bacterial structure(contd..)

18. Bacterial structure(contd..)

19.  What is Peptidoglycan
 Peptidoglycan is a complex, interwoven network that
surrounds the entire cell
 It is a complex polymer consisting of three parts:
 a backbone, composed of alternating N-
acetylglucosamine and N-acetylmuramic acid; and a
set of identical tetrapeptide side chains attached to
N-acetylmuramic acid; and a set of identical peptide
cross bridges.
Bacterial structure(contd..)

20. Bacterial structure(contd..)

21. Cell walls of Gram positive and Gram negative bacteria
 In gram-positive bacteria, there are as many as 40
sheets of peptidoglycan, comprising up to 50% of the
cell wall material.
 In gram-negative bacteria, there appears to be only
one or two sheets, comprising 5~10% of the wall
material.
Bacterial structure(contd..)

22. Bacterial structure(contd..)

23. Special components of Gram-Positive Cell Walls:
Teichoic Acids :These are water soluble polymers.
 Two types of teichoic acids: wall teichoic acid (WTA),
covalently linked to peptidoglycan, and membrane teichoic
acid, covalently linked to membrane glycolipids are called
lipoteichoic acids (LTA).
The medical importance of teichoic acids
 Induce septic shock when caused by certain gram positive
bacteria
 Teichoic acids also mediate the attachment of
staphylococci to mucosal cells.
Bacterial structure(contd..)

24.  Special components of Gram-negative Cell Walls
 An outer membrane containing lipopolysaccharide
(Lipid A + polysaccharide)which is an endotoxin and
responsible for endotoxic shock
 A periplasmic space where β-lactamases are found
 Peptidoglycan layer is very thin
Bacterial structure(contd..)

25. Structures outside the cell wall
 Capsule
 Flagella
 Pili (Fimbriae)
 Glycocalyx (slime layer)
Bacterial structure(contd..)

26. Capsule: -Many bacteria are surrounded by a discrete
covering layer of a relatively firm gelatinous material
composed of polysaccharide that lies outside and
immediately in contact with the cell wall.
Functions:
 Determinant of virulence
 Identification of an organism
 Capsular polysaccharides are used as the antigens in
certain vaccines
 Adherence of bacteria to human tissues
Bacterial structure(contd..)

27. Flagella: Flagella are long, whip like appendages that
help in the movement of bacteria.
They are composed of many subunits of protein
flagellin.
Medical Importance:
 Flagella may play a role in pathogenesis by propelling
the bacteria towards the site of infection e.g. E. coli
and Proteus species (common pathogens of UTI).
 Identification of bacteria e.g. Salmonella species
Bacterial structure(contd..)

28.  Monotrichous
Single polar flagellum
 Lophotrichous
multiple polar flagella
 Peritrichous
flagella distributed
over the entire cell
Bacterial structure(contd..)

29.  Pili (Fimbriae): Many gram-negative bacteria possess rigid
surface appendages called pili (L "hairs") or fimbriae (L
"fringes"). They are shorter and finer than flagella; they are
composed of structural protein subunits termed pilins.
Two types
 Ordinary pili (used for attachment)
 Sex pili (forms the attachment between the male (donor)
and the female (recipient) bacteria during conjugation) .
Bacterial structure(contd..)

30. Bacterial structure(contd..)

31. Bacterial structure(contd..)