Overview
This lecture covered the fundamental similarities and differences between prokaryotic and eukaryotic cells, including their structures, functions, and key defining features.
Classification and Evolution
- All living organisms are classified as either prokaryotes or eukaryotes based on cellular structure.
- Prokaryotes were the first life forms; eukaryotes evolved from prokaryotes via endosymbiosis.
- Endosymbiosis involved one prokaryote engulfing another, leading to organelles like mitochondria.
Shared Features of All Cells
- Both prokaryotes and eukaryotes possess DNA, a plasma membrane, cytoplasm, and ribosomes.
Key Differences: Prokaryotes vs Eukaryotes
- Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes have both.
- Prokaryotes are usually unicellular and smaller (0.1–5 μm); eukaryotes are often multicellular and larger (10–100 μm).
- Prokaryotic DNA is usually circular and found in the cytoplasm; eukaryotic DNA is linear and stored in the nucleus.
- Prokaryotes include bacteria and archaea; eukaryotes include animals, plants, fungi, algae, and protozoans.
- Transcription and translation are coupled in prokaryotes but separate in eukaryotes.
Prokaryotic Cell Structure and Features
- DNA is found in a nucleoid region, not a nucleus.
- Have ribosomes for protein synthesis, a cell wall (usually with peptidoglycan), a plasma membrane, and sometimes capsules.
- May have pili (for attachment and DNA transfer) and flagella (for movement).
- Do not have mitochondria, endoplasmic reticulum, or Golgi apparatus.
Eukaryotic Cell Structure and Features
- Possess a nucleus containing chromatin (DNA and proteins).
- Contain membrane-bound organelles such as mitochondria, endoplasmic reticulum, and in some cases, chloroplasts.
- May have a cell wall (in plants and fungi), cytoskeleton, vesicles, and vacuoles.
- Nucleolus inside the nucleus synthesizes ribosomal RNA.
- Ribosomes synthesize proteins; mitochondria generate energy.
Key Terms & Definitions
- Prokaryote — Unicellular organism lacking a nucleus and membrane-bound organelles; includes bacteria and archaea.
- Eukaryote — Organism whose cells contain a nucleus and various membrane-bound organelles.
- Nucleus — Membrane-bound organelle containing eukaryotic DNA.
- Nucleoid — Region in prokaryotes where DNA is located, not membrane-bound.
- Endosymbiosis — Process where one cell engulfs another, leading to organelles like mitochondria.
Action Items / Next Steps
- Review cell diagrams and be able to label key structures of prokaryotic and eukaryotic cells.
- Compare and contrast the features of prokaryotic and eukaryotic cells in preparation for quizzes or exams.