Lec 2 cell bio_SA_MTI

Differences and Similarities between Gram Positive and Gram Negative Bacteria

• Gram Positive Bacteria:

  • Thick peptidoglycan cell wall

  • Capsules present

  • Fewer structures (fimbriae, pili)

• Gram Negative Bacteria:

  • Thin peptidoglycan cell wall

  • Outer membrane of lipopolysaccharide

  • Structures: fimbrae, inclusion bodies, plasmids, flagella

Prokaryotic Cell Structure Components

1. Cell Wall: Shapes the cell, protects against stress.

2. Cytoplasm: Gel-like component with enzymes and organelles.

3. Cell Membrane: Regulates substance entry/exit.

4. Pili: Attachment structures.

5. Flagella: Whip-like appendages for movement.

6. Ribosomes: Sites of protein synthesis.

7. Plasmids: Non-chromosomal DNA.

8. Nucleoid Region: Contains genetic material.

External Structures of Bacteria

• Glycocalyx:

  • Protective sugar coat; varies in composition.

  • Protects against dehydration and nutrient loss.

• Capsules:

  • Organized, firm structure helping in moisture retention and protection against engulfment.

• Flagella:

  • Movement appendages; types include:

    • Polar/Monotrichous

    • Lophotrichous

    • Amphitrichous

    • Peritrichous

• Fimbriae and Pili:

  • Used for attachment, not motility.

  • Fimbriae are shorter and more numerous than pili.

Bacterial Cell Wall Characteristics

• Functions of Cell Wall:

  • Provides shape and protects cell integrity.

  • Chemical composition aids in bacterial classification.

• Peptidoglycan Composition:

  • Basic structure; consists of polysaccharides linked by peptides.

  • N-Acetylglucosamine (NAG) and N-Acetylmuramic acid (NAM) are key components.

Gram Positive vs. Gram Negative Cell Walls

• Gram Positive:

  • Multi-layered peptidoglycan; contains teichoic acids.

• Gram Negative:

  • Thin peptidoglycan; outer membrane with lipopolysaccharides.

Functions of Gram Negative Outer Membrane

• Acts as a barrier to antibiotics and digestive enzymes.

• Contains porins allowing passage of small molecules.

Lipopolysaccharide in Gram Negative Bacteria

• Lipid A: Endotoxin causing fever/shock in bloodstream.

• O Polysaccharides: Function as antigens for species identification.

Summary of Characteristics

• Gram Positive Bacteria:

  • Retain crystal violet, thick peptidoglycan, teichoic acids present.

• Gram Negative Bacteria:

  • Decolorized, accept counterstain, thin peptidoglycan, outer membrane with lipopolysaccharides.