Introduction to Prokaryotes and Eukaryotes

Prokaryotes and Eukaryotes

• All living organisms are categorized into two fundamental types of cells: prokaryotic and eukaryotic.
• This distinction is based on cellular structure and complexity.
• Prokaryotes include bacteria and archaea, while eukaryotes encompass a broad range of organisms including animals, plants, fungi, and protists.

Prokaryotes

• Prokaryotes are unicellular organisms that lack a defined nucleus and membrane-bound organelles. They are simpler and smaller than eukaryotic cells.

Characteristics of Prokaryotes:

Cell Structure:

1. Nucleus: No true nucleus; instead, they have a nucleoid region where the DNA is located.
2. DNA: Single, circular chromosome. Plasmids (small circular DNA molecules) may also be present.
3. Cell Membrane: Surrounded by a plasma membrane and often a rigid cell wall.
4. Ribosomes: Smaller (70S) than those in eukaryotic cells.
5. Organelles: Lack membrane-bound organelles. Functions are carried out in the cytoplasm or at the cell membrane.
6. Size: Smaller, typically 0.1-5.0 µm in diameter.

Reproduction:

• Binary Fission: Asexual reproduction where the cell divides into two genetically identical cells.

Examples:

• Bacteria (e.g., Escherichia coli, Streptococcus)
• Archaea (e.g., Methanogens, Halophiles)

Eukaryotes

• Eukaryotes are organisms whose cells contain a true nucleus and membrane-bound organelles.
• They can be unicellular or multicellular, and they exhibit a higher level of complexity than prokaryotic cells.

Characteristics of Eukaryotes:

1. Cell Structure:

   • Nucleus: Defined, membrane-bound nucleus containing the cell’s genetic material.
   • DNA: Linear chromosomes within the nucleus.
   • Cell Membrane: Plasma membrane encloses the cell. In plants, fungi, and some protists, there is also a rigid cell wall.
   • Ribosomes: Larger (80S) than those in prokaryotic cells.
   • Organelles: Presence of membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and (in plants and some protists) chloroplasts.
   • Size: Larger, typically 10-100 µm in diameter.

2. Reproduction:

   • Mitosis and Meiosis: Mitosis for asexual reproduction and growth; meiosis for sexual reproduction leading to genetic diversity.

3. Examples:

   • Animals (e.g., Humans, Insects)
   • Plants (e.g., Trees, Flowers)
   • Fungi (e.g., Yeasts, Mushrooms)
   • Protists (e.g., Amoeba, Algae)

Key Differences Between Prokaryotes and Eukaryotes

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