"Why did the cells become round?"
Kana tilted her head while looking through the microscope.
"What reagent did you add?" Rei asked.
"Colchicine... I think," Toma answered.
Rei nodded. "That's it. Colchicine depolymerizes microtubules. The cells lost their shape because the skeleton broke down."
"Skeleton? Cells have bones?"
"Not exactly bones, but there's a structure called the cytoskeleton. It maintains cell shape and serves as tracks for internal transport."
Toma showed interest. "What kind of structure?"
"Mainly three types. Microtubules, actin filaments, and intermediate filaments."
Kana wrote in her notebook. "How are they different?"
"Microtubules are thick and rigid. They're made of polymerized tubulin protein. The spindle during cell division is also made of these."
"What did colchicine destroy?"
"Microtubules. That's why cells became round. They couldn't maintain their shape."
Toma looked through the microscope. "You're right. They're all spherical."
Rei continued. "Actin filaments are thinner. They're involved in muscle contraction too. Important for cell movement and supporting the cell membrane."
"What about intermediate filaments?"
"Intermediate thickness. They provide mechanical strength. So cells can withstand being pulled."
Kana thought. "The three types divide the roles."
"Yes. Microtubules are roads, actin is muscle, intermediate filaments are reinforcement."
Toma asked. "But how do they transport things? Roads alone don't move anything."
"Good question. There are molecular machines called motor proteins."
"Molecular machines?"
"Proteins called kinesin and dynein. Using ATP as energy, they walk along microtubules."
Kana was surprised. "They walk?"
"It's a metaphor, but they actually advance step by step with leg-like structures. They carry vesicles and organelles on their backs."
Toma searched for an animation. "Is this it? It's really walking!"
On the screen was kinesin advancing along a microtubule on two legs.
"Amazing... just like a human," Kana admired.
Rei added. "Dynein walks in the opposite direction. Using the polarity of microtubules, they create a one-way transport system."
"Polarity?"
"Microtubules have directionality. Plus end and minus end. Kinesin goes to the plus end, dynein to the minus end."
Toma organized his thoughts. "So the cytoskeleton isn't just support. It's also a logistics system."
"Exactly. In nerve cells, materials can be transported tens of centimeters from the cell body to the axon tip."
"Tens of centimeters? For a cell?"
"Nerve cells are exceptionally long. Without the cytoskeleton, nutrients couldn't reach the axon tip."
Kana became serious. "What if the cytoskeleton breaks down?"
"Cells lose shape, transport stops. Cell division becomes impossible."
"Like in our experiment just now."
"Yes. Some anticancer drugs target microtubules. To stop cancer cell division."
Toma pondered. "But normal cells are affected too, right?"
"They are. That's why there are side effects. Especially cells that divide frequently are affected."
Kana summarized. "The cytoskeleton is involved in cell shape, transport, and division. It doesn't just gently support but actively works."
"Accurate understanding," Rei acknowledged.
Toma said, "I can't believe there's such a complex system inside cells."
"Molecules are working in invisible places. That's life."
The three looked through the microscope again. The rounded cells were gradually beginning to regain their shape.