Prokaryotes: Cell Structure Quiz

Prokaryotes: Cell Structure

• Prokaryotic cells are significantly simpler than eukaryotic cells, lacking membrane-bound organelles like mitochondria or a nucleus.
• They are typically smaller, ranging from 0.1 to 5 µm in diameter.
• Cell walls composed of peptidoglycan are a defining feature in most bacteria, providing structural support and protection. The specific composition and arrangement of peptidoglycan are utilized to differentiate bacterial species using staining techniques like Gram staining.
• Cell membranes enclose the cytoplasm; they are selectively permeable, regulating the flow of substances into and out of the cell.
• Prokaryotic cells may possess internal membrane systems like mesosomes, which increase the surface area for biochemical reactions.
• Flagella, pili, and fimbriae are common appendages used for motility, attachment, and conjugation.
• Flagella are whip-like structures that facilitate movement.
• Pili are thinner filamentous structures used for adhesion and conjugation (transferring genetic material between cells).
• Fimbriae are short, bristle-like appendages mostly used for attachment to surfaces.
• Cytoplasm contains ribosomes, which are protein synthesis machinery. The ribosomes of prokaryotes are smaller than those in eukaryotes.
• Some prokaryotes contain internal storage granules that store nutrients.
• Genetic material is typically a single, circular chromosome located in the nucleoid region, a non-membrane-bound area. Extrachromosomal plasmids are frequently found.
• Plasmids are small, circular DNA molecules that replicate independently of the chromosome. Plasmids often carry genes that provide advantages, such as antibiotic resistance.

Genetic Exchange in Prokaryotes

• Genetic diversity in prokaryotes is significantly promoted through several mechanisms of horizontal gene transfer.
• Transformation involves the uptake of "naked" DNA from the environment by a competent recipient cell, which may integrate it into its own genome.
• Conjugation involves the direct transfer of genetic material between two bacterial cells that are in contact. This typically involves a pilus connecting the cells, facilitating plasmid transfer. Transfer of chromosomal material is generally less frequent than plasmid transfer.
• Transduction is the transfer of genetic material between bacteria by a virus (bacteriophage). The virus acts as a vehicle carrying bacterial DNA from a donor cell to a recipient cell. This can result in the introduction of new traits into the recipient cell.
• These mechanisms contribute to the rapid evolution and adaptation of prokaryotes in diverse environments.
• Genetic exchange is crucial for the spread of antibiotic resistance genes between bacteria.
• Selection pressures, such as exposure to antibiotics stimulate genetic exchange between prokaryotic species.

Test your knowledge on the structure and characteristics of prokaryotic cells. This quiz covers key features, including cell walls, membranes, and appendages. Challenge yourself to understand the unique aspects that differentiate prokaryotes from eukaryotes.