Cells come in two main flavors: prokaryotic and eukaryotic. Prokaryotes are simple, lacking membrane-bound organelles. Eukaryotes are complex, with organelles like the nucleus, mitochondria, and endoplasmic reticulum. These differences shape how cells function and evolve.

The evolution from prokaryotes to eukaryotes was a game-changer. Eukaryotic cells developed compartments for specific jobs, boosting efficiency. The nucleus protects DNA, while mitochondria power the cell. This complexity allowed for the diversity of life we see today.

Prokaryotic and Eukaryotic Cell Structure

Prokaryotic vs eukaryotic cell structures

• Prokaryotic cells lack membrane-bound organelles, while eukaryotic cells possess them
  • Allows for compartmentalization of cellular functions in eukaryotic cells, leading to increased efficiency and specialization (lysosomes for digestion, mitochondria for energy production)
• Prokaryotic cells contain a nucleoid region where the genetic material is located, while eukaryotic cells have a true nucleus enclosed by a nuclear envelope
  • Provides better protection and regulation of genetic material in eukaryotic cells
• Prokaryotic cells have a cell wall composed of peptidoglycan, while eukaryotic cells may have a cell wall composed of cellulose (plants) or chitin (fungi)
• Both prokaryotic and eukaryotic cells possess a cell membrane
• Prokaryotic cells contain smaller ribosomes (70S) for protein synthesis, while eukaryotic cells have larger ribosomes (80S)
• Prokaryotic cells may have additional structures such as flagella (motility), pili (attachment), and capsules (protection), while eukaryotic cells have a cytoskeleton composed of microfilaments, intermediate filaments, and microtubules (cell shape, movement, and organization)

Major eukaryotic cell organelles

• Nucleus contains the cell's genetic material (DNA), surrounded by a nuclear envelope with nuclear pores
  • Site of DNA replication and transcription
• Endoplasmic reticulum (ER) has two types: rough ER studded with ribosomes for protein synthesis and modification, and smooth ER lacking ribosomes for lipid synthesis and detoxification
• Golgi apparatus modifies, packages, and sorts proteins and lipids for transport to their destination (secretory vesicles)
• Mitochondria are the site of cellular respiration and ATP production, containing their own DNA and ribosomes (evidence for endosymbiotic theory)
• Lysosomes contain digestive enzymes for intracellular digestion and cellular waste disposal and recycling
• Peroxisomes contain enzymes for detoxification (hydrogen peroxide breakdown) and lipid metabolism
• Chloroplasts (plants) are the site of photosynthesis, containing their own DNA and ribosomes (evidence for endosymbiotic theory)

Genetic material in cell types

• Prokaryotic cells have circular DNA located in the nucleoid region, not associated with histones
  • Lack a true nucleus
• Eukaryotic cells have linear DNA located within the nucleus, associated with histones to form chromatin and chromosomes
  • Possess a true nucleus enclosed by a nuclear envelope

Evolution of cell structures

• Prokaryotic cells are considered more primitive and evolved earlier than eukaryotic cells
• Eukaryotic cells are thought to have evolved from prokaryotic cells through endosymbiosis
  1. Mitochondria and chloroplasts are believed to have originated from prokaryotic cells that were engulfed by a larger cell
  2. These organelles retain their own DNA and ribosomes, supporting the endosymbiotic theory
• The presence of membrane-bound organelles in eukaryotic cells allows for:
  • Compartmentalization of cellular functions
  • Increased efficiency and specialization
• The evolution of a true nucleus in eukaryotic cells provides:
  • Better protection and regulation of the genetic material
  • More complex gene expression and regulation