Prokaryotes

Differentiate between Prokaryotes and Eukaryotes

• Prokaryotes: No nucleus, have a cell wall, lack organelles.

• Eukaryotes: Have a nucleus, no cell wall, contain organelles (e.g., mitochondria, chloroplasts, ER).

Identify clinically important bacteria based on microscopic appearance (gram - vs gram +)

• Microscopy: Used to examine cell shape, color (stain), and size.

• Gram Stain: Key differential method in microbiology.

• Gram-Positive: Multiple layers of peptidoglycan, teichoic/lipoteichoic acids.

• Gram-Negative: Outer membrane (LPS), thinner peptidoglycan, molecular sieve function

Gram­-positive bacteria

–Thick cell wall-more resistant to desiccation and tolerate dry conditions. They have no flagella, so they lack motility. Gram-(+) bacteria retain the purple color because their thick peptidoglycan layer does not allow the dye to escape.

Gram-negative bacteria

– Thin cell wall-thrive in damp situations and are generally more resistant to antibiotics. The alcohol extracts the high lipid content from their outer membrane, making it permeable. As a result, the crystal violet-iodine complex diffuses out, and these bacteria become colorless.

• Bacterial Shapes:

  • Cocci (spherical)

  • Bacilli (rod-shaped)

  • Curved/Spiral (e.g., spirochetes)

• Special Bacteria:

  • Mycobacteria: Stained by Ziehl-Neelsen due to waxy cell envelope.

  • Mycoplasma: No cell wall, smallest bacteria.

Define the role of certain cellular structures in the pathogenesis of infection

• Flagella: Motility (chemotaxis) via rotation.

• Pili: Adherence to host tissues.

• Capsules & Slime Layers: Polysaccharide/protein layers protect against phagocytosis and antibiotics, aid in adherence.

• Spores: Formed by Gram-positive bacteria (e.g., Clostridium) for survival in adverse conditions.

• Biofilms: Protect bacteria, difficult to treat (e.g., Pseudomonas in CF, S. epidermidis in catheters).

Describe the processes involved in bacterial growth

• Binary Fission: Main method of bacterial division.

• Selective Pressure: Mutants that survive hostile conditions thrive and multiply.

• Growth Requirements:

  • Energy: Catabolism of carbs, lipids, proteins.

  • Nutrients: Water, carbon, nitrogen, salts, iron.

  • Environmental Factors: Temperature, pH, O2 (anaerobic vs. aerobic bacteria).

Describe the structure of bacterial DNA and the process of DNA replication

• Bacterial Genome: Circular, double-stranded DNA (dsDNA), 4000 genes, 5M base pairs.

• DNA Structure: Nucleotides with bases (A, T, G, C), deoxyribose sugar, phosphate backbone.

• Supercoiling: DNA gyrase (Type II topoisomerase) relieves tension for replication/transcription.

• DNA Replication (Semi-conservative process)

  • Initiation: Origin of replication (oriC), Helicase unwinds dsDNA to ssDNA.

  • Elongation: DNA polymerase adds nucleotides in the 5’ to 3’ direction.

  • Proofreading: DNA polymerase corrects errors.

  • Termination: Two identical daughter helices are formed.

• Enzymes Involved: Helicase, DNA polymerase, ligase, gyrase.

Explain bacterial gene expression (transcription and translation)

• Gene Structure: Bacterial genes exist individually or in operons (uncommon in eukaryotes).

• Transcription:

  • Initiation: RNA polymerase binds to promoter, unwinds dsDNA.

  • Elongation: RNA polymerase transcribes dsDNA to mRNA.

• Translation:

  • mRNA: Template for decoding by ribosome.

  • tRNA: Transfers amino acids to ribosome to form protein.

  • Ribosome: Decodes mRNA into amino acid sequence (peptide chain)

Describe the clinical significance of plasmids and DNA mutation

• Plasmids:

  • Small, extrachromosomal, circular DNA.

  • Replicate independently, transferred between cells.

  • Carry antibiotic resistance genes (e.g., hospital-acquired bacteria).

• Mutations:

  • Types: Substitution, insertion, deletion.

  • Effects:

    • Substitution: May alter protein but could be silent.

    • Deletion/Insertion: Frameshift mutations, possible premature stop codons, truncated proteins.

  • Mutation Causes: Spontaneous or induced (mutagens).

  • Impact: AMR (antimicrobial resistance), evolution of virulence.