2.1.5 Structure of Prokaryotic Cells

Key Features of Prokaryotic Cells:

1. Cell Wall:

• A rigid outer layer made of peptidoglycan (also known as murein), a polymer of sugars and amino acids.
• Provides structural support and protection against osmotic pressure.

2. Capsule:

• A protective slimy layer outside the cell wall.
• Helps the cell to:
• Retain moisture.
• Adhere to surfaces (e.g., in the formation of biofilms).
• Offers protection against the immune response of host organisms.

3. Plasmid:

• A small, circular piece of DNA separate from the chromosomal DNA.
• Contains genes for survival traits, such as antibiotic resistance.

4. Flagellum:

• A tail-like structure that rotates to propel the cell through its environment.

5. Pili:

• Thin, hair-like projections on the surface of the cell.
• Used to:
• Attach to other bacterial cells or surfaces.
• Transfer genetic material during conjugation.

6. Ribosomes:

• The site of protein synthesis.
• Smaller than eukaryotic ribosomes, identified as 70S ribosomes.

7. Mesosomes:

• Infoldings of the inner cell membrane.
• Believed to:
• Contain enzymes required for aerobic respiration.
• Increase surface area for metabolic reactions.

Viruses (Comparison to Prokaryotic Cells):

• Non-living structures, unlike cells.
• Made of:
  1. Nucleic acid (DNA or RNA) as genetic material.
  2. A protective protein coat called the capsid.
  3. Some viruses are surrounded by a lipid layer known as the envelope.
• Lack a cellular structure and do not carry out life processes independently.

Organisation in Multicellular Organisms:

• In contrast to prokaryotes, multicellular organisms have:
  • Cells organised into tissues.
  • Tissues grouped into organs.
  • Organs working together in systems.