Prokaryotic Cells Overview

Definition of Prokaryotic Cells

• Prokaryotic cells are single-celled microorganisms and among the earliest life forms on Earth.
• They include two domains: Bacteria and Archaea.
• Photosynthetic prokaryotes, such as cyanobacteria, are capable of performing photosynthesis.
• Composed of a single membrane, all cellular reactions occur within the cytoplasm.
• Can be free-living organisms or exist as parasites.

Characteristics of Prokaryotic Cells

• Lack a nuclear membrane; instead, the genetic material is located in the nucleoid region of the cytoplasm.
• Can exhibit various shapes: spherical (cocci), rod-shaped (bacilli), or spiral (spirilla).
• Do not contain organelles typical of eukaryotic cells, such as mitochondria, endoplasmic reticulum, or Golgi bodies.

Structure of Prokaryotic Cells

• Plasma Membrane: A protective phospholipid layer that separates the interior of the cell from the external environment.
• Cytoplasm: A jelly-like substance where cellular components are suspended.
• DNA: Circular DNA serves as genetic material, directing protein synthesis and regulating cell activities.
• Ribosomes: Site of protein synthesis; some prokaryotes may also have cilia and flagella for movement.

Reproduction in Prokaryotes

• Prokaryotes primarily reproduce through binary fission, a simple division process.
• Recombination occurs via gene transfer between bacteria through:
  • Conjugation: Direct transfer of DNA between two bacteria.
  • Transformation: Uptake of free DNA from the environment.
  • Transduction: Transfer of DNA between bacteria via viruses.

Examples of Prokaryotic Cells

• Bacterial Cells:

  • Found in diverse environments, from soil to the human body; they exhibit varied shapes and structures.
  • Cell wall composed of peptidoglycan which provides structural integrity.
  • Unique structures include pili for attachment, flagella for motility, and capsules for protection.
  • Can carry plasmids, which are small, circular pieces of DNA.
  • Capable of forming endospores to survive harsh environmental conditions.

• Archaeal Cells:

  • Unicellular and similar in shape/size to bacteria, but often found in extreme environments like hot springs.
  • Cell walls lack peptidoglycan and have distinct lipid membranes with unique stereochemistry.
  • Possess a circular chromosome and plasmids, similar to bacteria, but have differences in biochemistry.