Prokaryotic Reproduction and Energy Acquisition

Reproduction in Prokaryotes

  • Most prokaryotes reproduce asexually through binary fission.

    • Binary fission: A cell divides into two genetically identical cells.

    • Process:

      1. The prokaryote's chromosome replicates.

      2. The original chromosome and the new copy separate.

      3. The cell elongates.

      4. A new piece of plasma membrane and cell wall forms, separating the cell into two identical cells.

    • Under ideal conditions, binary fission can occur rapidly (e.g., every 20 minutes).

      • Example: One bacterium can become 1,000,000,000b bacteria in 10 hours.

  • Conjugation: Some prokaryotes exchange genetic information.

    • Two prokaryotes attach to each other.

    • Pilus: Facilitates attachment and transfer of genetic material.

    • Results in new gene combinations and increased diversity.

Prokaryotes and Oxygen

  • Anaerobic prokaryotes: Do not use oxygen for growth or metabolism.

  • Obligate anaerobes: Cannot live or grow in the presence of oxygen.

    • Obtain energy through fermentation.

  • Facultative anaerobes: Can grow with or without oxygen.

  • Obligate aerobes: Require oxygen to grow.

How Prokaryotes Obtain Energy

  • Classification by energy source for cellular respiration or fermentation:

    • Heterotrophs: Cannot synthesize their own food; must ingest nutrients.

      • Many are saprotrophs (saprobes).

      • Obtain energy by decomposing organic molecules from dead organisms or organic waste.

    • Photosynthetic autotrophs: Carry out photosynthesis similarly to plants.

      • Require light and live in areas like shallow ponds and streams.

      • Synthesize organic molecules for food.

      • Formerly called "blue-green algae" (thought to be eukaryotes).

      • Renamed cyanobacteria upon discovery as prokaryotes.

      • Ecological importance:

        • Base of some food chains.

        • Release oxygen into the environment.

        • Cyanobacteria are thought to have been the first organisms to release oxygen into Earth's early atmosphere (approximately three billion years ago).

    • Chemoautotrophs: Autotrophs that don't require light.

      • Obtain energy by breaking down and releasing inorganic compounds (e.g., nitrogen or sulfur).

      • Chemosynthesis: The process of breaking down inorganic compounds.

        • Examples: Ammonia and hydrogen sulfide.

      • Ecological Importance:

        • Chemoautotrophs keep nitrogen and other inorganic compounds cycling through ecosystems.