Its all about bacteria structure

1. Structure of Bacterial Cells

2. Shape and Size of Bacteria:
• Classification by Shape:
– Bacteria are classified into three basic shapes: cocci (round),
bacilli (rods), and spirochetes (spiral-shaped).
– Some bacteria are pleomorphic, meaning they can take on
various shapes.
• Arrangement:
– Arrangement of bacteria is important, with cocci forming pairs
(diplococci), chains (streptococci), or grapelike clusters
(staphylococci).
– Arrangement of rods and spirochetes is less emphasized.
• Size:
– Bacteria range in size from about 0.2 to 5 μm.
– Mycoplasma, the smallest bacteria, are about the size of the
largest viruses.

4. Structure of Bacteria:
• Cell Wall:
• Composition:
– The cell wall is common to all bacteria except Mycoplasma.
– Composed of peptidoglycan, providing structural support and
maintaining cell shape.
• Gram-Positive vs. Gram-Negative Bacteria:
– Gram-positive bacteria have a thicker peptidoglycan layer and may
contain teichoic acid.
– Gram-negative bacteria have a complex outer layer with
lipopolysaccharide (endotoxin) and a periplasmic space.
• Properties of the Cell Wall:
– Acts as an antigen for laboratory identification.
– In gram-negative bacteria, contains endotoxin (lipopolysaccharide).
– Porin proteins facilitate the passage of molecules into the cell.

6. • Peptidoglycan:
• Composition:
– Complex, interwoven network surrounding the entire
bacterial cell.
– Composed of N-acetylmuramic acid, N-
acetylglucosamine, and tetrapeptides with unique
amino acids.
• Significance:
– Provides rigid support, maintains cell shape, and
withstands low osmotic pressure.
– Target for antibacterial drugs like penicillins.

7. • Lipopolysaccharide (LPS):
• Components:
– Composed of lipid A (toxic component), core
polysaccharide, and outer polysaccharide.
– Acts as endotoxin in gram-negative bacteria.
• Teichoic Acid:
• Location:
– Found in the outer layer of gram-positive cell walls.
• Functions:
– Induces inflammation and septic shock.
– Mediates attachment of staphylococci to mucosal cells.

8. • Cytoplasmic Membrane:
• Composition:
– Composed of a phospholipid bilayer similar to eukaryotic
cells.
• Functions:
– Active transport, energy generation, synthesis of cell wall
precursors, and secretion of enzymes/toxins.
• Cytoplasm:
• Composition:
– Amorphous matrix containing ribosomes, nutrient
granules, metabolites, and plasmids.
– Inner nucleoid region with bacterial DNA.

9. • Ribosomes:
• Function:
– Site of protein synthesis.
– Smaller (70S) in bacteria compared to eukaryotic
ribosomes (80S).
• Plasmids:
• Characteristics:
– Extrachromosomal, circular DNA capable of
independent replication.
– Carry genes for antibiotic resistance, toxins, pili, and
other functions.

12. Structures Outside the Cell Wall:
• Capsule:
– Gelatinous layer composed of polysaccharide or
polymerized d-glutamic acid.
– Determines virulence, aids identification, used in vaccines,
and facilitates adherence.
• Flagella:
– Whiplike appendages for movement toward nutrients.
– Identified by specific antibodies, some species cause
infections.
• Pili (Fimbriae):
– Hairlike filaments for adherence to human cell surfaces.
– Include sex pili for conjugation.

13. • Glycocalyx (Slime Layer):
– Polysaccharide coating aiding adherence to surfaces.
– Important in biofilm formation.
• Bacterial Spores:
– Highly resistant structures formed in adverse conditions.
– Found in Bacillus and Clostridium genera.
– Resist heat, dehydration, and chemicals; crucial for
sterilization.
• These components collectively contribute to the
diverse structure and functions of bacteria, influencing
their pathogenicity and interactions with hosts and
environments.