Cell Biology: Smooth ER and Lysosomes

Cell Structure and Function

• Cells are the basic units of life, enclosed by a membrane. They have varying structures and functions
• The cell is a complex system of interacting structures, each performing a specific task
• A cell's structure is interconnected, with one part affecting another

Cytoplasmic Organelles

• Cytoplasm: The jelly-like substance inside the cell. Contains dissolved substances
• Smooth Endoplasmic Reticulum (SER): Produces lipids and steroids, involved in detoxification. Abundant in cells that produce hormones
• Rough Endoplasmic Reticulum (RER): Covered in ribosomes and produces proteins intended for export
• Ribosomes: Involved in protein synthesis, can be free-floating or attached to RER
• Golgi Apparatus: Modifies, sorts, packages, & transports proteins received from the ER
• Lysosomes: Contain digestive enzymes to break down waste and cellular debris
• Mitochondria: The powerhouses of the cell, producing ATP (cellular energy) through cellular respiration. Abundant in high-energy cells such as muscle. Membrane-bound organelle.
• Centrioles: Essential for cell division, involved in organizing the microtubules that guide chromosomes during cell division. Pair of cylindrical structures.
• Microvilli: Finger-like projections on the cell membrane that increase surface area for absorption. Found on cells involved in absorption
• Nucleolus: Found inside the nucleus, it makes ribosomes. A dense region of the nucleus
• Nucleus: The control center of the cell, containing DNA and regulating cell activities. Double-layered membrane. Has chromosomes carrying genes.
• Nuclear Envelope: The membrane surrounding the nucleus. Continuous with the endoplasmic reticulum.
• Plasma Membrane: The outer boundary of the cell. Regulates the passage of substances in and out of the cell.

Endoplasmic Reticulum

• Tubular network continuous with the nuclear membrane.
• Rough ER (RER): Granular appearance (ribosomes), specializing in protein synthesis
• Smooth ER (SER): Agranular, involved in lipid synthesis, detoxification
• Different functions in different cell types

Functions of Smooth ER

• Lipid synthesis (e.g., in testes and adrenal glands)
• Calcium ion storage for muscle contraction
• Detoxification (e.g., in liver)

Ribosomes

• Small dense granules composed of ribosomal RNA (rRNA) and proteins
• Found free in cytoplasm or attached to RER.
• Function in protein synthesis (both free and bound).

Golgi Apparatus

• Composed of flattened sacs known as cisternae.
• Modifies, sorts, and packages proteins and lipids received from the ER.
• Packages into vesicles for different destinations (secreted proteins, cell membrane components, and lysosomes).

Lysosomes

• Membrane-bound vesicles containing digestive enzymes
• Digest macromolecules within the cell or foreign materials
• Crucial for waste breakdown and recycling

Cytoskeleton

• Network of protein fibers giving the cell shape, structure, and movement
• Includes microtubules, microfilaments, and intermediate filaments
• Maintains cell shape, anchors organelles, and assists in movement
• Involved in cell motility and determining cell shape

Centrioles and Cilia/Flagella

• Centrioles are involved in cell division.
• Cilia and flagella are microtubule-based extensions of the cell surface
• Cilia and flagella are involved in cellular movement. Basal bodies, at the base of cilia and flagella, are similar to centrioles.

Mitochondria

• Rod-shaped organelles with double membranes (cristae)
• Contain their own DNA
• Site of cellular respiration (ATP production)
• Abundant in high-energy cells (muscle cells)

The Nucleus

• Largest organelle, enclosed by a double membrane (nuclear envelope)
• Contains DNA (genetic material) organized into chromatin
• Controls cell activities via gene expression regulation
• Contains nucleoli where ribosomes are synthesized