Prokaryotes vs Eukaryotes Comparison

Prokaryotes: Defined as simple cells that lack a membrane-bound nucleus and specialized membrane-bound organelles.
- Examples: Bacteria and Archaea.
Eukaryotes: Defined as complex cells containing a membrane-bound nucleus as well as various membrane-bound organelles.
- Examples: Animals, Plants, Fungi, and Protists.

Cell Size:
- Prokaryotes: Extremely small, ranging from $0.1-5\,\mu m$ .
- Eukaryotes: Significantly larger, ranging from $10-100\,\mu m$ .
Cytoskeleton:
- Prokaryotes: Feature a simple cytoskeleton structure.
- Eukaryotes: Possess a complex and well-developed cytoskeleton.

Nucleus:
- Prokaryotes: The nucleus is absent. The genetic material is located in a non-enclosed region known as the nucleoid.
- Eukaryotes: A true nucleus is present, where the DNA is enclosed within a nuclear membrane.
DNA Structure:
- Prokaryotes: Typically consist of a single circular chromosome.
- Eukaryotes: Consist of multiple linear chromosomes.
Histone Proteins:
- Prokaryotes: Generally absent in bacteria, though notably present in archaea.
- Eukaryotes: Present and used for DNA packaging.
Plasmids:
- Prokaryotes: Common.
- Eukaryotes: Rare.

Membrane-Bound Organelles:
- Prokaryotes: Completely absent.
- Eukaryotes: Present; examples include the mitochondria, endoplasmic reticulum (ER), and the Golgi apparatus.
Ribosomes:
- Prokaryotes: Smaller $70S$ ribosomes, composed of $30S$ and $50S$ subunits.
- Eukaryotes: Larger $80S$ ribosomes, composed of $40S$ and $60S$ subunits.

Cell Wall:
- Prokaryotes: Usually present. In bacteria, the wall is composed of peptidoglycan.
- Eukaryotes: Present in plants (composed of cellulose) and fungi (composed of chitin). Cell walls are absent in animal cells.
Flagella:
- Prokaryotes: Simple structure composed of the protein flagellin; utilize a rotary movement mechanism.
- Eukaryotes: Complex microtubule structure organized in a $9+2$ arrangement; utilize a whip-like movement mechanism.

Cell Division:
- Prokaryotes: Divide via binary fission.
- Eukaryotes: Divide via mitosis and meiosis.
Reproduction:
- Prokaryotes: Exclusively asexual.
- Eukaryotes: Can be sexual, asexual, or both.

Transcription Location:
- Prokaryotes: Occurs in the cytoplasm.
- Eukaryotes: Occurs within the nucleus.
Translation Location:
- Prokaryotes: Occurs in the cytoplasm.
- Eukaryotes: Occurs in the cytoplasm after the mRNA has exited the nucleus.
Transcription & Translation Coupling:
- Prokaryotes: These processes occur simultaneously (coupled).
- Eukaryotes: These processes occur separately (not coupled).
Introns:
- Prokaryotes: Rare or absent.
- Eukaryotes: Common.
mRNA Processing:
- Prokaryotes: Minimal or entirely absent.
- Eukaryotes: Extensive; includes the addition of a $5'$ cap, a poly-A tail, and the process of splicing.
Gene Organization:
- Prokaryotes: Genes are often arranged in functional units called operons.
- Eukaryotes: Usually organized with one gene per promoter.

Energy Production:
- Prokaryotes: Occurs at the plasma membrane.
- Eukaryotes: Occurs within the mitochondria.
Photosynthesis:
- Prokaryotes: Utilizes internal membrane systems (as seen in cyanobacteria).
- Eukaryotes: Occurs within specialized organelles called chloroplasts (found in plants and algae).

Quick Exam Summary: Prokaryotes:
- No nucleus.
- No membrane-bound organelles.
- Circular DNA.
- $70S$ ribosomes.
- Binary fission.
- Co-occurring transcription and translation.
- Examples: Bacteria and Archaea.
Quick Exam Summary: Eukaryotes:
- Nucleus present.
- Membrane-bound organelles present.
- Linear chromosomes.
- $80S$ ribosomes.
- Mitosis and meiosis.
- Spatiotemporal separation of transcription (nucleus) and translation (cytoplasm).
- Examples: Animals, plants, fungi, and protists.
Memory Trick: "Pro = Primitive, Eu = True":
- Prokaryote: Translates to "before nucleus," indicating the lack of a true nucleus.
- Eukaryote: Translates to "true nucleus," indicating the presence of a legitimate nucleus within the cell.