Facilitated vs. Active Transport

• Facilitated Diffusion:

  • Nature: Passive process, does not require energy (ATP).
  • Mechanism: Involves transport proteins to help molecules cross the membrane.
  • Examples: Small uncharged molecules like water, oxygen, carbon dioxide, and nitrogen can pass through membranes via simple diffusion.

• Active Transport:

  • Nature: Active process, requires energy which usually comes from the hydrolysis of ATP into ADP.
  • Mechanism: Also requires transport proteins but actively moves substances against their concentration gradient.

Group Translocation and Protein Secretion

• Group Translocation:

  • Mechanism where a molecule is transported across a membrane and is chemically modified (e.g., phosphorylation).

• Protein Secretion:

  • Nature of proteins: Macromolecules that usually cannot pass through the membrane due to size and charge.
  • Process: Proteins are transported out of the cell via transport proteins, fold into their tertiary structure upon exit, enabling them to perform their function.

Bacterial Cell Walls and Peptidoglycan

• Cell Wall Importance: Protects against osmotic pressure, preventing lysis (cell rupture).
• Types of Bacteria:
  • Gram Positive: Thick peptidoglycan layer, interacts with antimicrobial drugs more effectively.
  • Tachylic Acids: Present, help anchor peptidoglycan to the membrane.
  • Gram Negative: Thin peptidoglycan layer surrounded by an outer membrane, making them more resistant to antimicrobial treatment.
  • Periplasmic Space: Area between the inner and outer membranes that contains enzymes and proteins.
  • Lipopolysaccharide (LPS): Composed of lipid A (immunogenic), a core polysaccharide, and an O antigen; can provoke immune responses.

Antibiotics Targeting the Cell Wall

• Mechanism of Action:
  • Antibiotics like penicillin inhibit transpeptidase, the enzyme necessary for peptidoglycan cross-linking.
  • Unique to bacteria, thus they do not affect human cells, making them selective.

Gram Staining Process

• Steps in Gram Staining:

  • Crystal Violet Stain: Stains all cells initially.

  • Decolorization: Different impact on Gram-positive (remains purple) vs. Gram-negative (loses color).

  • Counter Stain (Safranin): Stains Gram-negative cells pink, allowing differentiation between the two.

  • Understanding Results: Gram-positive cells retain crystal violet due to heavy peptidoglycan locking in the dye, whereas Gram-negative cells' thinner peptidoglycan allows the dye to wash out.

External Structures of Bacteria

• Flagella:

  • Function: Motility through rotation; arranged in various ways (polar, peritrichous).
  • Mechanism: Movement can be either a run (smooth) or tumble (random change in direction).

• Pili:

  • Function: Facilitate attachment and can assist in DNA transfer (e.g., sex pilus).
  • Cooperation between cells promotes genetic exchange, often including antibiotic resistance.

Internal Structures of Bacteria

• Cytoplasm: Contains ribosomes, nucleoid with bacterial chromosome, and plasmids (additional genetic element).
• Ribosomes:
  • Prokaryotic ribosomes consist of a 30S small subunit and a 50S large subunit, forming a 70S ribosome, which is distinct from eukaryotic ribosomes (80S).
• Cytoskeleton: Similar to eukaryotic structure, supports cell shape and function.

Endospores

• Formation: During unfavorable conditions, some bacteria form endospores, which are resistant to extreme conditions and can survive without nutrients.
• Mechanism: The endospore develops inside the bacterial cell, causing the cell to disintegrate and leaving a resilient structure behind.

Conclusion and Review

• Antimicrobial Targets: Understanding the structure and function of bacterial cells assists in developing antibiotic strategies, highlighting the importance of targeting processes unique to bacteria.
• Critical for Exam Preparation: Focus on mechanisms of transport, cell wall composition, Gram staining, and antibiotic actions for a thorough understanding of microbiological principles.