outline key structural features of a prokaryotic cell as found in a typical bacterium, including: • unicellular • generally 1–5 µm diameter • peptidoglycan cell walls • circular DNA • 70S ribosomes • absence of organelles surrounded by double membranes

Sourav PanOctober 28, 2024

Answered

Key Structural Features of a Prokaryotic Cell (Typical Bacterium)

I. Overall Cell Characteristics

• Unicellular: Exists as a single cell, not part of a multicellular organism.
• Size: Generally ranges from 1–5 µm in diameter (micrometers), though some bacteria can be larger or smaller.
• Shape: Varies among species; common shapes include:
  • Spherical (Cocci)
  • Rod-shaped (Bacilli)
  • Spiral (Spirilla)
  • Comma-shaped (Vibrio)

II. Cell Envelope

• Peptidoglycan Cell Wall (Murein):
  • Provides structural support and maintains cell shape.
  • Composed of a polymer of sugars cross-linked by short peptides.
  • Thickness and composition can vary among different bacterial species, influencing their response to antibiotics (e.g., Gram staining differentiation).

III. Genetic Material

• Circular DNA (Nucleoid):
  • Single, circular chromosome lacking a nuclear membrane.
  • Located in a region of the cell called the nucleoid.
  • No histone proteins to compact DNA; instead, other proteins help manage DNA structure.

IV. Protein Synthesis Machinery

• 70S Ribosomes:
  • Smaller than eukaryotic 80S ribosomes, reflecting differences in protein synthesis processes.
  • Composed of two subunits (50S and 30S).
  • Responsible for translating mRNA into proteins.

V. Absence of Membrane-Bound Organelles

• No Mitochondria, Chloroplasts, Endoplasmic Reticulum, Golgi Apparatus, etc.:
  • Metabolic processes, including energy production and protein modification, occur in the cytoplasm or are associated with the cell membrane.
  • Simpler cellular organization compared to eukaryotic cells.

Additional Features (Not Always Present but Common in Many Bacteria)

• Flagella: For motility, composed of flagellin protein.
• Pili/Fimbriae: Short, hair-like appendages for adhesion to surfaces or other cells.
• Capsule/Slime Layer: A protective, gelatinous layer outside the cell wall, aiding in evasion of the host’s immune system.
• Plasmids: Small, circular, self-replicating DNA molecules separate from the chromosomal DNA, often carrying genes for antibiotic resistance or other beneficial traits.

Visual Representation:

Imagine a small, simple cell with:

• A peptidoglycan wall providing structure
• A circular DNA coil (nucleoid) without a membrane
• 70S ribosomes scattered throughout the cytoplasm
• No membrane-bound organelles
• Possibly equipped with flagella, pili, a capsule, or plasmids, depending on the bacterial species.