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What is a Prokaryote?

  • There are two basic types of organisms based on cell type: Prokaryotic and Eukaryotic.

    • Prokaryotic cells are divided into the domains Bacteria and Archaea.

    • Eukaryotic cells make up the more familiar Domain Eukarya.

  • Prokaryotes are the smallest forms of life that can live independently.

  • The most familiar prokaryotes are bacteria.

    • Bacteria are a very diverse group that have several shapes, depending on the species.

    • The archaea are also quite diverse, but resemble the bacteria in general appearance.

  • Some prokaryotes, mainly in domain Archaea, can live in extreme environments.

    • Extreme thermophiles live in hot places such as volcanic springs and hydrothermal vents.

    • Extreme halophiles live in water of high saline content, and acidophiles thrive at very low pH.

    • Methanogens are poisoned by oxygen and live in places like swamps and the gut of animals.

    • Many biologists believe that if life exists elsewhere in our solar system, it will resemble thermophiles and methanogens; fossils of prokaryotes in meteorites have recently been reported.

    • Prokaryotes have been utilized as sources of enzymes that work under extreme conditions.

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Prokaryotic Cells: What Structures Are Present in All Cells?

  • There all several essential structures that all cells must have to survive.

  • The plasma membrane separates the cell from its environment and serves as a "gate keeper".

    • The membrane has a lipid-protein structure.

    • Phospholipids provide fluidity within the membrane and form a selectively permeable barrier.

    • Hydrophobic substances and some small molecules can move through the lipid layers by diffusion.

    • Membrane proteins play a crucial role in moving hydrophilic substances across the membrane; some proteins can move molecules against a concentration gradient, as you will learn later in the course.

    • Membrane proteins can also function as enzymes or as signal transducers.

  • The genome within a chromosome serves as the control center for the cell.

  • Ribosomes are the "work bench" on which proteins are made; the resulting proteome gives cells their specific structure and function.

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Prokaryotic Cells: What Are Some Additional Features of These Cells?

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