Untitled Flashcard Set

1. Parts & Functions of a Microbial Cell

(Typical prokaryotic cell)

Cell membrane (plasma membrane) – Selective barrier; transport, energy generation (ETC), signal sensing

Cell wall – Shape, protection from osmotic lysis

Cytoplasm – Metabolic reactions

Nucleoid – Circular chromosome (no membrane)

Ribosomes (70S) – Protein synthesis

Capsule / slime layer – Protection, adhesion, virulence

Pili / fimbriae – Attachment, conjugation

Flagella – Motility

Inclusions – Storage (carbon, phosphate, sulfur)

2. Cell Membrane vs Cell Wall

Feature Cell Membrane Cell Wall

Composition Phospholipid bilayer + proteins Peptidoglycan (bacteria)

Function Transport, metabolism, signaling Shape, rigidity, osmotic protection

Selectivity Selectively permeable Not selectively permeable

Presence All cells Most bacteria, archaea, plants

⚠ Membrane = function & transport

⚠ Wall = structure & protection

3. Gram-Positive vs Gram-Negative

Feature Gram-Positive Gram-Negative

Peptidoglycan Thick Thin

Outer membrane ❌ No ✅ Yes

Teichoic acids Present Absent

LPS (endotoxin) ❌ No ✅ Yes

Gram stain Purple Pink

Antibiotic sensitivity More sensitive More resistant

🧠 Clinical tip:

Gram-negative bacteria are harder to kill due to the outer membrane + LPS.

4. Transport Across the Membrane – Mechanisms

Passive Transport (No Energy)

Simple diffusion – Small, nonpolar molecules (O₂, CO₂)

Facilitated diffusion – Via proteins, down gradient

Active Transport (Energy Required)

Primary active transport – Uses ATP directly (ABC transporters)

Secondary active transport – Uses proton motive force

Symport (same direction)

Antiport (opposite direction)

Group Translocation

Molecule chemically modified during transport

Example: PTS system (glucose phosphorylation)

5. Archaeal Differences (vs Bacteria)

No peptidoglycan (often pseudopeptidoglycan or protein S-layer)

Ether-linked membrane lipids (more stable in extremes)

Unique rRNA & transcription machinery

Some have histone-like proteins

Can live in extreme environments (heat, salt, acid)

🧠 Archaea are prokaryotic in structure but eukaryotic-like in genetics.

6. Cell Division & Cytoskeleton Functioning

Cell Division

Binary fission

DNA replication

Chromosome segregation

Septum formation

Cell separation

Cytoskeletal Proteins

FtsZ – Forms Z-ring at division site (tubulin-like)

MreB – Maintains rod shape (actin-like)

CreS – Curvature in some bacteria

➡ Prokaryotes do have a cytoskeleton, just simpler.

7. Specialized Microbial Structures (Structure / Function / Evolution)

Examples:

Endospores – Survival in harsh conditions (evolved for dormancy)

Capsules – Immune evasion & adhesion

Gas vesicles – Buoyancy in aquatic microbes

Magnetosomes – Orientation in magnetic fields

🧬 Evolutionarily selected for environmental survival & competitiveness.

8. Flagellar Motion & Chemotaxis

Flagellar Structure

Filament – Movement

Hook – Flexibility

Basal body – Motor (uses proton motive force)

Motion

CCW rotation → Run (straight)

CW rotation → Tumble (direction change)

Chemotaxis

Movement toward attractants and away from repellents

Controlled by signal transduction proteins (Che proteins)