Differences between Prokaryotic and Eukaryotic Cells

Overview of Cell Types

Understanding the fundamental differences between prokaryotic and eukaryotic cells is essential in microbiology. These differences impact cellular processes, genetic organization, and the complexity of organisms.

• Prokaryotic cells: Simple, unicellular organisms lacking a true nucleus and membrane-bound organelles. Examples include Bacteria and Archaea.

• Eukaryotic cells: More complex cells with a true nucleus and various membrane-bound organelles. Found in Protists, Fungi, Plants, and Animals.

Key Differences

• Nucleus: Prokaryotes lack a nucleus; eukaryotes have a membrane-bound nucleus.

• Organelles: Prokaryotes lack membrane-bound organelles; eukaryotes possess them (e.g., mitochondria, endoplasmic reticulum).

• DNA Structure: Prokaryotic DNA is typically circular and found in the nucleoid region; eukaryotic DNA is linear and contained within the nucleus.

• Cell Division: Prokaryotes divide by binary fission; eukaryotes divide by mitosis (and meiosis for gametes).

• Endosymbiotic Theory: Suggests that some eukaryotic organelles (e.g., mitochondria, chloroplasts) originated from symbiotic prokaryotes.

Key Processes

• Protein Synthesis: Both cell types synthesize proteins, but ribosome structure differs (70S in prokaryotes, 80S in eukaryotes).

• DNA Replication: Both replicate DNA, but mechanisms and enzymes involved can differ.

Mutations

Types and Effects of Mutations

Mutations are changes in the DNA sequence that can affect gene function and phenotype. They are a source of genetic variation and can be caused by errors in DNA replication or external factors.

• Substitution Mutation: One base is replaced by another in the DNA sequence.

• Deletion Mutation: One or more bases are removed from the DNA sequence.

• Insertion Mutation: One or more bases are added to the DNA sequence.

Types of Substitution Mutations

• Neutral Mutation: Does not affect the function of the protein.

• Missense Mutation: Results in a different amino acid in the protein, potentially altering function.

• Nonsense Mutation: Introduces a premature stop codon, leading to a truncated, usually nonfunctional protein.

Conjugation

Horizontal Gene Transfer in Bacteria

Conjugation is a process by which bacteria exchange genetic material through direct contact. It is a form of horizontal gene transfer, contributing to genetic diversity and the spread of traits such as antibiotic resistance.

• Plasmids: Small, circular DNA molecules that can carry genes for antibiotic resistance (resistance plasmids) or fertility (F plasmids).

• Fertility Plasmid (F plasmid): Encodes genes for pilus formation, enabling conjugation.

• Conjugation: Transfer of genetic material (usually plasmids) from one bacterium to another via a pilus.

• Transformation: Uptake of free DNA from the environment by bacteria.

• Griffith's Experiment: Demonstrated transformation in Streptococcus pneumoniae, showing that genetic material could be transferred between bacteria.

Summary Table: Types of Horizontal Gene Transfer

Some Common Species of Eukaryotes Causing Diseases

Pathogenic Eukaryotes

Several eukaryotic organisms are responsible for human diseases. These include protists, fungi, and helminths (parasitic worms).

• Entamoeba histolytica: A protist causing amoebic dysentery (diarrhea).

• Tinea unguium: A fungal infection causing brittle nails.

• Tinea pedis: Fungal infection known as athlete's foot.

• Trypanosoma brucei: Protist causing African sleeping sickness.

• Schistosoma species: Blood flukes (helminths) causing schistosomiasis.

• Plasmodium malariae: Protist causing malaria.

• Giardia: Protist causing giardiasis (diarrhea).

• Trichomonas vaginalis: Protist infecting the vagina, causing trichomoniasis.

• Slime mold: Not typically pathogenic to humans, but can affect plants by blocking sunlight and causing yellowing of leaves.

Summary Table: Eukaryotic Pathogens and Associated Diseases