Biology Chapter: The Cell

Cell Structure and Function

• Plasma Membrane: Lipid bilayer of phospholipids and cholesterol, controls substance movement, enables intercellular communication, and contains recognition markers.
• Nucleus: Double membrane with pores; houses DNA regulating protein synthesis and cell functions, features nucleoli for ribosomal RNA production.

Cytoplasmic Organelles

• Ribosomes: Composed of ribosomal RNA and proteins; sites of protein synthesis found as free ribosomes or attached to rough endoplasmic reticulum.
• Rough Endoplasmic Reticulum (RER): Membranous tubules with attached ribosomes; synthesizes and transports proteins to the Golgi apparatus.
• Smooth Endoplasmic Reticulum (SER): Membranous tubules without attached ribosomes; manufactures lipids, detoxifies chemicals, stores calcium.
• Golgi Apparatus: Stacked membrane sacs; modifies, packages, and distributes proteins and lipids for secretion or internal use.
• Lysosomes: Membrane-bound vesicles containing digestive enzymes for material breakdown.
• Peroxisomes: Membrane-bound vesicles involved in lipid and amino acid degradation, breakdown hydrogen peroxide.
• Proteasomes: Complexes that degrade proteins in the cytoplasm.
• Mitochondria: Double-membraned organelles; major ATP production sites in the presence of oxygen.
• Centrioles: Cylindrical organelles that assist in microtubule formation and cell division.
• Cilia: Extensions that move materials over cell surfaces; contain microtubules.
• Flagellum: Propels sperm in humans; extension of the plasma membrane.
• Microvilli: Increases plasma membrane surface area for absorption and secretion; modified for sensory functions.

Fluid Mosaic Model

• Describes the non-rigid, dynamic structure of the plasma membrane.

Transport Mechanisms

• Sodium-Potassium Concentration: Essential for cell volume and generating electrical signals.
• Secondary Active Transport: Uses ion concentration gradients established by primary active transport to move substances across membranes; involves symporters (same direction) and antiporters (opposite direction).

Endocytosis Types

• Receptor-Mediated Endocytosis: Selective uptake of specific ligands via receptor binding and vesicle formation.
• Phagocytosis: Engulfing of large particles by phagocytes (e.g., macrophages, neutrophils); forms phagosomes that fuse with lysosomes for digestion.
• Bulk-phase Endocytosis (Pinocytosis): Uptake of extracellular fluid; vesicles containing fluid detach from the plasma membrane.

Exocytosis

• Releases materials from cells via fusion of secretory vesicles with the plasma membrane; occurs in both secretory and nerve cells.

Transcytosis

• Vesicular transport across a cell, facilitating movement between blood plasma and interstitial fluid.

Osmosis

• Movement of water through selectively permeable membranes from higher to lower concentration until equilibrium; involves simple diffusion or aquaporins.

Principles of Osmosis

• Net water movement occurs when solute particles cannot pass through the membrane affecting cell volumes.
• Isosmotic Solutions: Equal osmotic pressure on both sides.
• Osmotic Pressure: Pressure needed to stop fluid movement across membranes.

Tonicity

• Isotonic Solution: Equal solute concentrations; maintains normal RBC shape (e.g., 0.9% NaCl).
• Hypotonic Solution: Lower solute concentration; causes RBCs to swell and potentially burst (hemolysis).
• Hypertonic Solution: Higher solute concentration; leads to cell shrinkage (crenation).

Dialysis

• Process using a semipermeable membrane to separate particles of different sizes, allowing small molecules to diffuse while retaining larger ones.

Explore the components and functions of cell parts in this quiz on cell biology. Understand the role of the plasma membrane and other organelles in maintaining cellular processes. Perfect for students studying biology at an advanced level.