3.Bacteria.pdf3.Bacteria.pdf3.Bacteria.pdf3.Bacteria.pdf3.Bacteria.pdf3.Bacteria.pdf3.Bacteria.pdf

bacteria

1. 2.2. Bacteria
•Bacteria are a large group of unicellular, Parasitic, saprophytic
and free living microorganisms.
•Varying in size from 0.1-10 µm long.
•They are a simple (single) cell structure contain both DNA and
RNA without a nucleus.
•They are capable of performing all essential process of life.
E.g. Growth, Metabolism and Reproduction (Multiplication)
•They multiply by a Process called binary fission.
•They are classified by their morphology, arrangement, staining
Reactions, Cultural characteristic, antigenic structure, and
increasingly by their genetic composition using specialized
molecular biological techniques.

2. 2.2. Bacteria

General property of bacteria
•Typical prokaryotic cell
•Contain both DNA and RNA
•Most grow in artificial media
•Replication is by binary fission
•Contain rigid cell wall
•Sensitive to antimicrobial agent

3. 2.2. Bacteria
2.2.1. Bacterial cell structure and functions
Bacterial cell structure considered at three levels.
1.Cell envelope proper:
–Cell wall, cell membrane, Glycocalyx (capsule and slime)
and Spores
2.Cellular element enclosed with in the cell
envelope:
–Mesosomes ribosome, Chromosomes and cytoplasmic
granules.
3.Cellular element external to the cell envelope or
appendages:
–Flagellum and Pilus.

4. Fig shows Bacterial Structure

5. 2.2. Bacteria

2.2.1. Bacterial cell structure and functions
1. Cell Envelope proper
A. Cell wall
•Multi layered structure and constitutes about 20% of the
bacterial dry weight Average thickness is 0.15-0.5 m.
•It is porous and permeable to substances of low molecular
weight.
•The rigid part of the cell wall is known as peptidoglycan.
•The structure of the bacterial cell wall differs in Gram-positive
and gram- negative bacteria.
–Components of cell wall of Gram negative bacteria
•Thin Peptidolycan (Thin cell wall)
•Lipoprotein
•Lipopolysaccharide
–Components of cell wall of Gram positive bacteria
•Thick Peptidoglycan (Thick cell wall)
•Teichoic acid

6. 2.2. Bacteria
2.2.1. Bacterial cell structure and functions
1. Cell Envelope proper
A. Cell wall
•The structure of the bacterial cell wall also
differs in Acid-fast and Non Acid-fast bacteria.
–The Acid-fast bacterial Cell-wall contain lipids
particularly Mycolic-acid lipid and the Mycolic acids
confer resistance to desiccation, most antibiotics and
phagocytosis for the bacterium.
–Non Acid-fast bacteria don’t contain lipids specially
mycolic acid.

7. 2.2. Bacteria

2.2.1. Bacterial cell structure and functions
1. Cell Envelope proper
A. Cell wall
Functions of Cell Wall
•Provides shape to the bacterium
•Gives rigidity to the organism
•Protects from environment
•Provides staining characteristics to the bacterium
•Contains receptor sites for phages
•Site of action of antibody and colicin
•Contains components toxic to host

8. 2.2. Bacteria
2.2.1. Bacterial cell structure and functions
1. Cell Envelope proper
B. Cell membrane
•Also named cytoplasmic membrane. It accounts for
30% of the dry weight of bacterial cell.
•It is composed of 60% protein, 20-30% lipids and
10-20% carbohydrate.
•Membrane lipids are strongly amphipathic
molecules with: a polar hydrophilic “head group” &
an apolar hydrophobic “tail”.
•Most of biological activities of the bacteria cell is
performed by the movement of the cell membrane;
Eg. Respiration.

9. 2.2. Bacteria
2.2.1. Bacterial cell structure and functions
1. Cell Envelope proper
B. Cell membrane
Function of Cell Membrane
•Regulates the transport of nutrients and waste
products into and out of the cell.
•Synthesis of cell wall components
•Assists DNA replication (Mesosomes)
•Secrets proteins
•Caries on respiration
•Captures energy in ATP

10. 2.2. Bacteria
2.2.1. Bacterial cell structure and functions
1. Cell Envelope proper
C. Glycocalyx (capsule and slime)
•Cellular Element External to the Cell Envelope or cell wall
made of sugars (polysaccharide) and they are two types.
1.Capsule is gel firmly adherent to cell envelope and highly
organized, tightly attached.
2.Slime is gel loosely organized and loosely attached.
Easily washed off from cell envelope.
Both serve to enable the bacteria to attach to tissues and
to resist phagocytic digestion (Phagocytosis).
All bacteria have at least a thin slime layer.
Few bacteria have capsule and vary among the different
species of bacteria.

11. 2.2. Bacteria

2.2.1. Bacterial cell structure and functions
1. Cell Envelope proper
D. Spores
•It is dehydrated, metabolically inactive and thick coat. Produced
in Resting, dormant cells.
•Structures which are capable of surviving/withstand under
adverse environmental extremes conditions like heat, drying,
freezing, action of toxic chemicals and radiation.
•It is produced by some Gram positive genera: such as in
Clostridium, Bacillus & Sporosarcina.
•It is the hardiest of all life forms and pressurized steam at 121
o
C
for 20-30 minutes will destroy it.
•It is significant in spread of disease and have a 2-phase life cycle
•Germination (vegetative cell) & Sporulation (endospore)
–Sporulation -Formation of endospores from vegetative cell
–Germination- Return to vegetative growth from endospore.

12. 2.2. Bacteria

2.2.1. Bacterial cell structure and functions
2. Cellular element enclosed with in the cell envelope:
A. Chromosome or genome
•The chromosome is DNA, which serves as the control centre of
the bacterial cell, carrying the genetic information needed for
producing several thousand enzymes and other proteins.
•It is capable of duplicating itself, of guiding cell divisions and of
directing cellular activities.
•Bacterial genome consists of single molecule of double stranded
DNA arranged in a circular form.
•It is not surrounded by a nuclear membrane and does not have
a definite shape.
•B. Ribosomes
•Ribosomes are the sites of protein synthesis.
•It is composed of RNA (70%) and proteins (30%) and constitutes
90% of the RNA and 40% of the total protein.

13. 2.2. Bacteria

2.2.1. Bacterial cell structure and functions
2. Cellular element enclosed with in the cell envelope:
C.Mesosomes
•They are vesicular convoluted or multi-laminated structure formed as
invaginations of cell membrane in the cytoplasm
•They involved (used) in DNA segregation and in the formation of cross
walls during cell ( Bacterial) division for multiplication.
•It also involved in respiratory enzyme activity.
D. Cytoplasmic Granules or inclusions bodies
•Intracellular storage bodies.
•Represent accumulated food reserves.
•Bacterial cell can use them when environmental sources are depleted.
•Inclusions are vary in size, number & content. Eg. - granules that store
Glycogen, large in size high in number.
E. Plasmids
•Plasmids are self-regulating extra-chromosomal DNA or genome.
•Plasmids carry the genes for the Antibiotic resistance which is .mediated
by a variety of enzymes.

14. 2.2. Bacteria
2.2.1. Bacterial cell structure and functions
3. Cellular element external to the cell envelope or appendages:
A. Flagellum
•It is the organ of locomotion in bacterial cell and much
longer than the bacterial cell.
•Flagella are helical thread like filaments, which produce
motility by rotation and composed of protein sub units
called flagellin.
Flagellar Arrangements
1.Atrichous: Bacteria with no flagellum
2.Monotrichous: Bacteria with single polar flagellum
3.Lophptrichous: Bacteria with bunch of flagella at one pole
4.Amphitrichous: Bacteria with flagella at both poles
5.Peritrichous: Bacteria with flagella all over their surface.

15. 2.2. Bacteria
2.2.1. Bacterial cell structure and functions
3. Cellular element external to the cell envelope or appendages:
B. Pilus(Fimbriae)
•They are hairs like, short, finer filaments extruding
from the cytoplasmic membrane and are made from
proteins called pilin.
•They are found in two forms and each has different
function.
–Common Pllli :- They are used for attachment (adhesion)
called common pilli
–Sex pilli :- used for transferring of genetic material from
one donor bacterium to another recipient bacterium
during the process of conjugation called sex pilli.

16. 2.2. Bacteria
2.2.2. Multiplication of bacteria
•Bacteria replicate or multiply by simple cell
division known as binary fission ( splitting in to
two)
–First the single piece of double stranded DNA
reproduces itself exactly in to two.
–The mother cell divided in to two by the help of
mesosomes and each organelle allocated in the two
daughters cells equally and then it became two
daughter cells.

17. Bacterial growth
•Bacteria do not have an obligatory life cycle. Whenever adequate nutrition
and conducive environment factors are available a bacterium enlarges and
eventually divides by binary fission to form two daughter cells.
•Nuclear division precedes cell division and, therefore, in a growing population,
many cell carrying two nuclear bodies can be found.

Fig. Bacterial binary fission