Prokaryotes: Simple but Diverse

Prokaryotes: Simple but Diverse

• Prokaryotes are the simplest and oldest known living organisms, being single-celled and lacking a nucleus or membrane-bound organelles.
• Derived from the Greek words "pro" (before) and "karyon" (nucleus), referencing the lack of a true nucleus.
• Exist in a vast range of environments, from extreme hot spots to freezing Arctic conditions.
• Divided into two major groups: Bacteria and Archaea.
• These two groups differ from each other and from Eukarya (organisms with complex cells).

Prokaryotic Cell Structure

• Simpler than eukaryotes: Prokaryotic cells lack a membrane-bound nucleus.
• Nucleoid: Their DNA isn't contained in a nucleus but instead resides in a region of the cytoplasm called the nucleoid.
• Cell Wall: A rigid outer layer providing support and protection, composed primarily of peptidoglycan in bacteria and different materials in archaea.
• Flagella and Pili: External appendages, flagella are whip-like structures for movement, and pili are hair-like structures for attachment.

Prokaryotic Genetic Material

• Circular Chromosome: Typically a single, circular chromosome located in the nucleoid region.
• Plasmids: Small, circular DNA molecules that can replicate independently and may carry genes for beneficial traits (e.g., antibiotic resistance).
• Conjugation: The process by which genetic material (plasmids) can be transferred between prokaryotic cells.

Prokaryotic Reproduction

• Binary Fission: A simple method of asexual reproduction where one cell splits into two identical daughter cells.

Prokaryotic Metabolism

• Autotrophs: Can produce their own food through photosynthesis (photoautotrophs) or chemosynthesis (chemoautotrophs).
• Heterotrophs: Obtain energy by consuming organic molecules from other organisms.
• Oxygen Needs: Heterotrophic prokaryotes differ in their oxygen requirements, including obligate aerobes (require oxygen), obligate anaerobes (cannot tolerate oxygen), and facultative anaerobes (can use or avoid oxygen depending on the environment).