Advanced Biology Study Notes: Cell Structure and Function (Topic 2.1)

Overview of Cellular Structure and Function

  • Generalized animal and plant cell models serve as foundational frameworks for topic 2.12.1 of the 20252025–20262026 Advanced Biology curriculum.

  • Real biological cells are specialized for specific physiological functions and differ from generalized models.

Ribosomes and Common Ancestry

  • Structure & Function: Composed of ribosomal RNA (rRNA\text{rRNA}) and proteins; execute protein synthesis (translation) by reading messenger RNA (mRNA\text{mRNA}) to assemble amino acids.

  • Evolutionary Significance: Present in all prokaryotes and eukaryotes, proving common ancestry from a single origin approximately 3.5×109 years3.5 \times 10^9\text{ years} ago.

The Endomembrane System

  • A coordinated network (RER, SER, Golgi complex, nuclear envelope) that modifies, packages, stores, and transports proteins, lipids, and polysaccharides.

  • Utilizes phospholipid membrane vesicles for intracellular routing and extracellular secretion.

Endoplasmic Reticulum: Smooth and Rough

  • Smooth ER (SER): Tubular network lacking ribosomes; synthesizes lipids (phospholipids, steroids) and performs chemical detoxification.

  • Rough ER (RER): Membrane sheets studded with ribosomes; synthesizes proteins into its lumen, packages them into transport vesicles, and aids compartmentalization.

Cellular Compartmentalization

  • Eukaryotic internal membranes create distinct compartments with specific microenvironments (e.g., pH, enzyme concentration), optimizing biochemical reactions and preventing metabolic interference.

Golgi Complex

  • Stacked, flattened membrane sacs (cisternae) acting as the cell's receiving and shipping hub.

  • Chemically modifies, folds, sorts, and packages RER products into vesicles for specific destinations.

Mitochondria and Cellular Respiration

  • Site of cellular respiration and ATP\text{ATP} synthesis (cellular energy currency).

  • Double-membrane organelle with a smooth outer membrane and a folded inner membrane that maximizes surface area for electron transport and enzyme activity.

Lysosomes and Apoptosis

  • Membrane-bound sacs of hydrolytic enzymes that digest cellular waste, foreign material, and damaged organelles.

  • Mediates apoptosis (programmed cell death) by releasing enzymes to degrade the cell in a controlled manner.

Vacuoles and Osmoregulation

  • Plant Central Vacuole: Large central sac responsible for osmoregulation; exerts hydrostatic turgor pressure against the cell wall for structural rigidity.

  • Animal Vacuoles: Smaller, multiple sacs used for localized storage.

Chloroplasts and Photosynthesis

  • Site of photosynthesis in plants and algae; converts radiant light energy into chemical energy (carbohydrates).

  • Double-membrane structure containing stacks of flattened thylakoid membrane discs housing photosynthetic pigments.

Diagrammatic Breakdown and Organelle Identification

  • Plant Cells: Identified by central vacuole, chloroplasts, cell wall, nucleus, ER, Golgi, lysosomes, and mitochondria.

  • Animal Cells: Identified by nucleus, ER, Golgi, mitochondria, ribosomes, lysosomes, and small storage vacuoles (lacking central vacuole and chloroplasts).