Origin and Evolution
Prokaryotic cells are the most ancient and simplest forms of life, dating back around 3.5 billion years. They represent the earliest form of cellular life and include bacteria and archaea.
Eukaryotic cells are believed to have evolved from prokaryotic cells around 1.5 billion years ago through a process known as endosymbiosis. They are more complex and include all plant, animal, fungal, and protist cells.
Cell Structure
Prokaryotic cells are generally smaller (0.1 to 5 micrometers in diameter) and lack a defined nucleus and other membrane-bound organelles. Their DNA is located in a region called the nucleoid.
Eukaryotic cells are larger (10 to 100 micrometers in diameter) and have a defined nucleus that houses their DNA. They contain various membrane-bound organelles, such as the mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
Genetic Material
Prokaryotic cells have a single, circular chromosome that is not enclosed in a membrane. They may also contain small, circular DNA molecules called plasmids, which carry additional genes.
Eukaryotic cells have multiple, linear chromosomes contained within a nuclear envelope. Their DNA is associated with histone proteins, forming a complex structure called chromatin.
Cell Division
Prokaryotic cells reproduce through a simple process called binary fission, where the cell divides into two identical daughter cells.
Eukaryotic cells divide through more complex processes: mitosis for somatic (body) cells and meiosis for reproductive (germ) cells. These processes ensure accurate distribution of chromosomes to daughter cells.
Cell Membrane and Wall
Prokaryotic cells have a plasma membrane surrounded by a rigid cell wall made of peptidoglycan (in bacteria) or other unique molecules (in archaea). Some also have an outer capsule for additional protection.
Eukaryotic cells have a plasma membrane made of a phospholipid bilayer with embedded proteins. Plant cells and some fungi also have a rigid cell wall made of cellulose or chitin, respectively.
Ribosomes
Prokaryotic cells have 70S ribosomes, which are smaller and simpler than those in eukaryotes. These ribosomes are involved in protein synthesis.
Eukaryotic cells have 80S ribosomes, which are larger and more complex. Ribosomes can be free-floating in the cytoplasm or attached to the endoplasmic reticulum, forming the rough ER.
Metabolic Pathways
Prokaryotic cells often perform metabolic processes in the cytoplasm or associated with the cell membrane. They can have unique pathways, such as nitrogen fixation in some bacteria.
Eukaryotic cells compartmentalize metabolic processes within specific organelles. For example, the mitochondria are the site of cellular respiration, while chloroplasts (in plants) perform photosynthesis.
Movement and Motility
Prokaryotic cells may have simple structures like flagella or pili for movement and attachment. These structures are composed of proteins and function differently from those in eukaryotes.
Eukaryotic cells can move using complex structures like cilia and flagella, which have a "9+2" arrangement of microtubules. Eukaryotic cells can also move through amoeboid motion or by forming pseudopodia.
Examples
Prokaryotic cells include bacteria (e.g., Escherichia coli, Streptococcus) and archaea (e.g., Methanogens, Halophiles).
Eukaryotic cells include animal cells (e.g., human cells), plant cells (e.g., leaf cells), fungal cells (e.g., yeast), and protist cells (e.g., amoebae).
Understanding the differences between prokaryotic and eukaryotic cells is fundamental in biology, as it highlights the diversity and complexity of life forms and their evolutionary relationships.
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