Overview
This lecture covers the structure and function of key eukaryotic cell organelles required for A-level biology, focusing on both plant and animal cells.
Eukaryotic Cell Organelles: Structure & Function
- The cell surface (plasma) membrane is a phospholipid bilayer with embedded proteins that controls entry and exit of substances.
- The nucleus has a double membrane (nuclear envelope) with pores, contains nucleoplasm, chromosomes, and a nucleolus for rRNA production.
- The nucleus is the site of DNA replication, transcription, and stores genetic information.
- The rough endoplasmic reticulum (RER) has ribosomes on its surface and is the site of protein synthesis.
- The smooth endoplasmic reticulum (SER) lacks ribosomes and is the site of lipid and carbohydrate synthesis and storage.
- The Golgi apparatus consists of curved, folded membranes (cisternae), modifies and packages proteins, forms glycoproteins, creates lysosomes, and transports materials in vesicles.
- Lysosomes are membrane-bound vesicles containing digestive enzymes to break down phagocytosed material, worn out organelles, and dead cells (autolysis).
- Mitochondria have a double membrane, inner folds (cristae), matrix, and their own DNA; site of aerobic respiration and ATP production.
- Ribosomes, made of rRNA and proteins, exist as 80S (eukaryotes) or 70S (prokaryotes) and synthesize proteins.
- Plant cell vacuoles are fluid-filled, bounded by a tonoplast membrane, provide structural support, and temporarily store sugars, amino acids, and pigments.
- Chloroplasts (in plants only) have a double membrane, thylakoid membranes (form grana), stroma, and are sites of photosynthesis; contain chlorophyll pigment.
- Plant cell walls are made of cellulose microfibrils, giving structural strength; fungal cell walls contain chitin.
- The plasma membrane is present in all cells and organelles, selectively permeable due to its structure (phospholipid bilayer, proteins, glycoproteins, glycolipids, cholesterol).
Key Terms & Definitions
- Organelle — a specialized cell structure with a specific function.
- Phospholipid bilayer — the double-layered structure forming cell membranes.
- Nucleus — contains genetic material and controls cell activities.
- Nucleolus — site of rRNA synthesis within the nucleus.
- Rough Endoplasmic Reticulum (RER) — membrane system with ribosomes for protein synthesis.
- Smooth Endoplasmic Reticulum (SER) — membrane system for lipid and carbohydrate synthesis.
- Golgi apparatus — modifies, sorts, and packages proteins and lipids.
- Lysosome — vesicle with digestive enzymes to break down substances.
- Mitochondrion — organelle for aerobic respiration and ATP production.
- Ribosome — structure for protein synthesis.
- Vacuole — storage and support organelle in plant cells.
- Chloroplast — site of photosynthesis in plant cells.
- Cell wall — provides structural support, made of cellulose in plants and chitin in fungi.
Action Items / Next Steps
- Review diagrams of each organelle and practice labeling.
- Test yourself on organelle functions and structures.
- Ensure you know definitions and differences between organelles for exam preparation.