1.1 eukaryotes and prokaryotes

1.1.1 Eukaryotes & Prokaryotes

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All living organisms are made up of cells. Cells can be classified into two main types: Eukaryotic and Prokaryotic cells.

Eukaryotic Cells:

  • Eukaryotes include all plants, animals, fungi, and protists.

  • These cells are more complex and usually larger than prokaryotic cells.

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Key features:

  • Nucleus: Contains the cell's genetic material (DNA) enclosed within a nuclear membrane.

  • Cell membrane: Controls the movement of substances in and out of the cell.

  • Cytoplasm: Gel-like substance where most chemical reactions happen.

  • Mitochondria: Where aerobic respiration occurs, providing energy for the cell.

  • Ribosomes: Sites of protein synthesis.

  • Chloroplasts (in plant cells): Site of photosynthesis, contains chlorophyll.

  • Cell wall (in plant cells): Made of cellulose, strengthens the cell.

Prokaryotic Cells:

  • Prokaryotes include bacteria and archaea.

  • These cells are simpler and generally smaller than eukaryotic cells.

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Key features:

  • No true nucleus: Genetic material (DNA) is not enclosed within a membrane; instead, it is a single loop of DNA found in the cytoplasm.

  • Plasmids: Small rings of DNA that can replicate independently of chromosomal DNA.

  • Cell membrane: Similar function to eukaryotes, controlling the movement of substances.

  • Cytoplasm: Contains ribosomes, but they are smaller than those in eukaryotes.

  • Cell wall: Provides structure and protection, but it is not made of cellulose.

  • Flagella (in some bacteria): Tail-like structures that help the cell move.

Differences Between Eukaryotic and Prokaryotic Cells:

  • Size: Eukaryotic cells are generally larger (10-100 micrometres) compared to prokaryotic cells (0.1-5 micrometres).

  • Nucleus: Eukaryotes have a nucleus; prokaryotes do not.

  • Organelles: Eukaryotes have membrane-bound organelles (e.g., mitochondria, chloroplasts); prokaryotes do not.

  • DNA Structure: Eukaryotes have linear DNA associated with proteins (histones); prokaryotes have circular DNA without histones.

  • Reproduction: Eukaryotic cells divide by mitosis or meiosis; prokaryotic cells divide by binary fission.

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Importance of Understanding:

  • The classification helps in understanding the complexity and functionality of different organisms.

  • Knowledge of these differences is essential for studies in genetics, microbiology, and cell biology.