Ultrastructure of Bacteria
BY:
FATIMA KHAN
1ST SEMESTER
ROLL NO :22
DEPT. OF BIOTECHNOLOGY
PATNA WOMEN’S COLLEGE
Introduction of Bacterial cells
.
Bacteria
are unicellular organisms belonging to the
prokaryotic group where the organisms lack a few
organelles and a true nucleus.
Bacteria are microscopic, single-celled organisms that
exist in their millions, in every environment, both inside
and outside other organisms.
Some bacteria are harmful, but most serve a useful
purpose.
They support many forms of life, both plant and animal,
and they are used in industrial and medicinal
processes.
Ultra structure of Bacteria
EXTERNAL STRUCTURES
Pili / Fimbriae
⚫ Numerous, short, thin,proteinaceous
fibers
which protrude from the surface.
⚫ Allow cells to attach to surfaces or other cells.
⚫ Besides the attachment pili, some species
produce conjugation pili that establish contact
between appropriate cells facilitating transfer of
genetic material.
Flagella
⚫ Long,hair-like
appendage composed of protein
and responsible for locomotion
⚫ Each flagellum is composed of a helical
filament, hook and basal body.
⚫ The hollow helical filament is composed of long,
rigid strands of protein, while the hook attaches
the filament to a basal body anchored in the cell
membrane
Bacterial types based on number
and arrangement of flagella
Type
Characteristic
Monotrichous
Lophotrichous
Amphitrichous
A single polar flagellum eg: Vibrio cholerae
A cluster of polar flagella eg: Spirillum
Flagella at both the ends either singly or in cluster Eg:
Aquaspirillum
Two or more flagella at one end of bacterial cell eg:
Pseudomonas
Cell surface evenly surrounded by several lateral flagella eg:
E.coli
Cells devoid of flagella eg: Lactobacillus
Cephalotrichous
Peritrichous
Atrichous
e
Glycocalyx
⚫
A viscous polysaccharide material covering
the bacterial cells to assist in attachment to a
surface and impart resistance to desiccation.
⚫ The layer can be thick and covalently
bound to the cell in which case it is known
as capsule.
⚫ Thinner, diffuse polysaccharides are
referred to as slime layer.
Bacterial Cell W all
⚫ Bacterial
cell wall is made up of
peptidoglycan
⚫ Peptidoglycan consists of chains of disaccharides
(glycan strands) cross-linked by peptide bridges.
⚫ Each disaccharide (also called murein), is
composed of two monosaccharides, N - acetyl
glucosam ine (N A G) and N - acetyl
muramic acid (NAM).
Structure of Cell wall
Cell membrane
⚫ 5 nm thick
⚫ 40%
phospholipid and 60% protein
⚫ Fluid in nature and the dynamic model of
membrane structure is called the fluid mosaic
model.
⚫ i.e.,cell membrane consists of a phospholipid
bilayer in which are embedded integral
membrane proteins.
Cytoplasm
⚫ Cell
membrane encloses the cytoplasm.
⚫ It is the compartment within which most growth
and metabolism occur.
⚫ Cytoplasm consists of the cytosol, a semifluid
mass of proteins, aminoacids, sugars, nucleotides,
salts, vitamins and ions all dissolved in water .
⚫ several bacterial sub structures, each with a
specific function.
Nucleoid
⚫ The chromosome region
in a prokaryotic cell
appears as a diffuse mass termed the nucleoid.
⚫ The nucleoid does not contain a covering
membrane.
⚫ It represents a central subcompartment in the
cytoplasm
⚫ Usually there is a single chromosome per cell
⚫ The nucleoid contains the cell’s essential
genetic information.
⚫ Most cells have one copy of each gene,and
hence the cells are genetically haploid.
D
Plasmid
⚫ Besides
a nucleoid, many prokaryotic cells
also contain smaller molecules of circular
D N A called plasmids.
⚫ Plasmids contain nonessential genetic
information.
⚫ These are extrachromosomal D N A molecule
and have about a tenth the size of a prokaryotic
chromosome.
⚫ These stable D N A molecules exist as closed
loops containing 5 to 100 genes.
⚫ There can be one or more plasmids in a cell
and these may contain similar or different genes.
Chemical
Composition
Function
External Structures
Pili
Protein
Attachment to surfaces
Genetic Transfer
Flagella
Protein
Motility
Glycocalyx
Polysaccharides
Buffer to environment
Attachment to surfaces
Structure
Cell Envelope
Cell Wall
Gram positives: thick
peptidoglycan +
teichoic acid
Cell protection Shape
determination
Prevents cell lysis
Gram negatives: little
peptidoglycan and an
outer membrane
Cell Membrane
Protein
Phospholipid
Cell Boundary
Transport into / out of cell
Site of enzymatic reactions
e
Chemical
Composition
Function
DNA
Site of essential genes
DNA
Site of non essential
Ribosomes
RNA and Protein
genes Protein synthesis
Inclusion
Glycogen, sulfur,
Nutrient storage
bodies
lipid Polyphosphate
Granules
Protein shells
Storage for ATP and
nucleic acids
Buoyancy
Structure
Internal Structures
Nucleoid
Plasmids
Gas vesicles