The cytoskeleton is the internal framework that gives a eukaryotic cell its shape, strength, and organization. It is not a rigid skeleton, but a living network of protein fibers that can grow, shrink, bend, and rearrange. This network helps cells move, divide, resist mechanical stress, and position organelles.
Understanding the cytoskeleton explains how cells act as organized, active systems rather than bags of fluid.
Key Facts
- Microfilaments are made of actin and are about 7 nm in diameter.
- Intermediate filaments are about 10 nm in diameter and provide tensile strength.
- Microtubules are made of tubulin and are about 25 nm in diameter.
- Motor proteins convert chemical energy into motion using ATP: ATP + H2O -> ADP + Pi + energy.
- Kinesin and dynein move cargo along microtubules, usually in opposite directions.
- The mitotic spindle is a microtubule-based structure that separates chromosomes during cell division.
Vocabulary
- Cytoskeleton
- The cytoskeleton is a dynamic network of protein filaments that supports cell shape, movement, transport, and division.
- Microfilament
- A microfilament is a thin actin-based fiber that helps cells change shape, move, and contract.
- Intermediate filament
- An intermediate filament is a rope-like protein fiber that helps cells resist stretching and mechanical stress.
- Microtubule
- A microtubule is a hollow tubulin-based tube that forms tracks for transport and structures such as the mitotic spindle.
- Motor protein
- A motor protein is a molecule that uses ATP energy to move along cytoskeletal filaments or move cellular cargo.
Common Mistakes to Avoid
- Thinking the cytoskeleton is fixed like bone is wrong because cytoskeletal filaments are constantly assembled, disassembled, and reorganized.
- Mixing up microtubules and microfilaments is wrong because microtubules are hollow tubulin tubes used for transport and division, while microfilaments are thin actin fibers used in shape change and contraction.
- Assuming organelles float randomly is wrong because many organelles are positioned and transported along cytoskeletal tracks by motor proteins.
- Forgetting ATP in motor protein movement is wrong because kinesin, dynein, and myosin require ATP hydrolysis to generate force and motion.
Practice Questions
- 1 A microtubule is 25 nm in diameter and a microfilament is 7 nm in diameter. How many times wider is the microtubule than the microfilament?
- 2 A vesicle travels 12 micrometers along a microtubule in 6 seconds. What is its average speed in micrometers per second?
- 3 A cell is treated with a drug that prevents microtubules from polymerizing. Explain how this could affect intracellular transport and chromosome separation during mitosis.