Cell Organelles: Structures and Functions

This study guide summarizes the main organelles and structures found in prokaryotic and eukaryotic cells, along with their key functions and descriptions. Understanding these components is fundamental to cell biology and is essential for students in General Biology courses.

Prokaryotic Cells

Prokaryotic cells are simpler, lacking a true nucleus and most membrane-bound organelles. However, they still contain essential structures for life processes.

• Nucleoid: Region containing compressed DNA; not surrounded by a membrane.

• Ribosome: Site of protein synthesis; smaller than eukaryotic ribosomes.

• Cell membrane: Boundary of the cell, composed mainly of lipids; controls entry and exit of substances.

• Cell wall: Provides structural support and shape; made up of polysaccharides (e.g., peptidoglycan in bacteria).

• Flagellum: Tail-like structure used for movement.

• Plasmids: Small, circular DNA molecules; often carry genes for antibiotic resistance.

• Cytoplasm: Gel-like substance where cellular processes occur.

Additional info: Prokaryotes do not have membrane-bound organelles such as mitochondria or chloroplasts.

Eukaryotic Cells

Eukaryotic cells are more complex, containing a variety of membrane-bound organelles that compartmentalize cellular functions.

• Nucleus: Contains the cell's DNA; surrounded by a nuclear envelope; site of ribosome synthesis in the nucleolus.

• Rough Endoplasmic Reticulum (Rough ER): Studded with ribosomes; synthesizes and transports proteins.

• Smooth Endoplasmic Reticulum (Smooth ER): Lacks ribosomes; involved in lipid synthesis and detoxification.

• Golgi Apparatus: Stacked, flattened sacs; modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles; known as the cell's "post office."

• Mitochondrion: Site of cellular respiration; produces ATP; contains an inner membrane and matrix space.

• Chloroplast: Site of photosynthesis in plant cells; contains thylakoids (green pancake-like sacs) and stroma (fluid-filled space).

• Vacuole: Stores food, water, and waste; provides turgor pressure in plant cells.

• Lysosome: Contains digestive enzymes; breaks down waste and cellular debris.

• Peroxisome: Involved in oxidation reactions and detoxification.

• Vesicle: Small membrane-bound sac for transport of substances within the cell.

• Plasma Membrane: Cell boundary made up of a lipid bilayer; regulates movement of substances in and out of the cell.

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that provide structural support, shape, and facilitate movement.

• Motor Proteins: Move organelles and vesicles along cytoskeletal tracks.

• Stroma: Fluid-filled space in chloroplasts surrounding the thylakoids.

• Thylakoid: Membranous sac within chloroplasts; site of the light-dependent reactions of photosynthesis.

Key Organelles and Their Functions

Examples and Applications

• Example: The mitochondrion is often called the "powerhouse of the cell" because it generates ATP through cellular respiration, a process essential for energy supply in both plant and animal cells.

• Example: Chloroplasts are found only in plant cells and some protists, enabling these organisms to convert solar energy into chemical energy via photosynthesis.

Key Equations

• Cellular Respiration (Mitochondria):

• Photosynthesis (Chloroplasts):

Comparison of Prokaryotic and Eukaryotic Cells