Cells College Bio 06 March 2025 at 13.38.09 PM

Prokaryotic vs. Eukaryotic Cells

Ribosomes:

• Non-membrane bound organelles found in both prokaryotic and eukaryotic cells.

• Function: Ribosomes play a crucial role in the process of translation, where they synthesize proteins by facilitating the reading of messenger RNA (mRNA) sequences and linking together amino acids in the correct order based on genetic instructions from DNA.

Nucleus:

• Prokaryotic Cells: Prokaryotic cells lack a true nucleus. Instead, their genetic material is concentrated in a region called the nucleoid, where the circular DNA molecule resides freely in the cytoplasm. This organization differs significantly from eukaryotes.

• Eukaryotic Cells: Eukaryotic cells contain a well-defined nucleus, which is the largest organelle. It is surrounded by a nuclear envelope comprised of two membranes that regulate the passage of molecules in and out of the nucleus. The nucleus houses the cell's genetic material (DNA), organized into linear chromosomes.

DNA Organization:

• Prokaryotic DNA: Found in the nucleoid region, which is not membrane-bound; genetic material consists of circular chromosomes, which are not associated with histone proteins as in eukaryotes.

• Plasmids: Additionally, prokaryotic cells can contain plasmids—small, circular DNA molecules that replicate independently of chromosomal DNA. These plasmids often carry genes that confer advantageous traits, such as antibiotic resistance.

• Eukaryotic DNA: Eukaryotic DNA is organized into linear chromosomes, which are tightly packed and wrapped around histone proteins to form chromatin within the nucleus.

Differences Between Prokaryotes and Eukaryotes:

• Nucleus: Eukaryotes possess a nucleus; prokaryotes do not, reflecting fundamental differences in cell organization.

• Size: Eukaryotic cells generally range between 10-30 micrometers, while prokaryotic cells typically measure around 0.1-5.0 micrometers, demonstrating the larger and more complex nature of eukaryotic cells.

• Membrane-bound Organelles: Eukaryotes have multiple membrane-bound organelles, such as mitochondria, chloroplasts (in plants), and lysosomes, which perform specific functions essential for cell survival, while prokaryotic cells rely solely on their cytoplasm for metabolic activities.

Organelles in Eukaryotic Cells

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; primarily involved in the synthesis of proteins that are either secreted from the cell or incorporated into the cell's membranes.

  • Smooth ER: Lacks ribosomes; plays roles in lipid synthesis, detoxification of harmful metabolic byproducts, and calcium ion storage, crucial for muscle contraction and other cellular signaling processes.

• Cytosol: The liquid portion of the cytoplasm, primarily consisting of water with dissolved ions, nutrients, and organic molecules. It provides the medium for biochemical reactions and is involved in transporting materials within the cell.

• Cytoskeleton: A dynamic network providing structural support, composed of three main types of filaments:

  • Microfilaments (Actin Filaments): Involved in cell motility, shape changes, and cytokinesis, the process of cell division.

  • Intermediate Filaments: Provide tensile strength and structural integrity, anchoring organelles in place.

  • Microtubules: Hollow tubes made from tubulin dimers; crucial for intracellular transport, cell shape maintenance, and separation of chromosomes during cell division.

Cell Walls

• Present in bacterial, fungal, and plant cells but absent in animal cells.

• Composition:

  • Plants: Cell walls are primarily composed of cellulose, a polysaccharide that provides rigidity and strength.

  • Fungi: Characterized by a cell wall made of chitin, which is a strong and flexible nitrogen-containing polysaccharide.

  • Bacteria: Have cell walls composed of peptidoglycan, a complex structure providing both rigidity and protection against osmotic pressure changes.

• Function: Cell walls provide structural stability, help maintain cell shape, and protect against environmental stressors.

Summary of Main Points

• Recognize the key differences between prokaryotic and eukaryotic cells, focusing on structural characteristics, organization of DNA, and presence of organelles.

• Understand the functions, structures, and compositions of ribosomes, cytosol, the cytoskeleton, and cell walls.

• Be able to identify and compare the compositions and functions of cell walls among different organisms while recognizing the significance of these features in relation to the respective lifestyles and environments of prokaryotes and eukaryotes.