Borrowing from Biology — Nature's Nanotechnology
by Dora Lee
When it comes to molecular manufacturing, why not turn to a real expert for advice? Nature's been making nano-size machines since life on earth began. With that kind of experience, maybe it can teach us a thing or two about making machines one millionth of a millimeter in size.
Machinery that is small needs motors and gears that are even smaller. Nanotechnologists are just starting to tackle that problem, but nature solved it a long time ago. Flagella are corkscrew-shaped propellers that transport bacteria like tiny motorboats. The long, stringy flagella, connected to a hook structure, fit over a rod that rotates inside a ring attached to the bacterium. As the rod rotates, the flagella twirl around, pushing water down and behind them to thrust the bacterium forward. The motion is a lot like the scooping one your hand makes while you're swimming.
Nature has also perfected the solar power factory. Ever wonder why plants need sunlight? The leaves of green plants contain chloroplasts – tiny factories that collect carbon dioxide, water, and sunlight for photosynthesis. Inside chloroplasts, chlorophyll molecules soak up the sun and pass it on to the reaction center. There, during photosynthesis, some of the energy is used to extract protons from water and to drive photosynthetic reactions. The rest is used to make ATP, an important fuel used by most living organisms, or glucose, which stores the energy until it's needed.
And let's not forget about ourselves. The human body is nothing but tiny factories working around the clock. Most of the things we do or feel are controlled by proteins, which are machines themselves.
Enzymes are proteins that set off biological reactions, and hormones are proteins that signal cells to change behavior. Their manufacture takes place inside our cells in factories called ribosomes. First, the instructions for making a protein are copied onto RNA from DNA, the genetic material inside our cells. Inserted into a ribosome, the RNA specifies what amino acid “parts” to use and where to put them. It even detects mistakes and corrects them! Finished proteins are sorted and “shipped” to destinations inside and outside the cells via a “conveyor belt” consisting of membranes called Golgi apparatus.
But how does all this help nanotechnologists? Well, nanotechnologists have found some of nature's designs useful to copy. For example, viruses are experts at sneaking into human cells, escaping the body's attempts to destroy them, and multiplying themselves. That's why they're so good at getting us sick! Taking advantage of these properties, scientists are experimenting with packaging genes into artificial viruses and sending them into patients to correct genetic diseases by replacing defective genes with normal ones. Of course, they remove the disease-causing parts of the virus first!
Liposomes are another example of man-made machines copied from nature. Many cancer-fighting drugs are great at killing cancer cells, but are toxic to healthy cells, too. Liposomes are bubbles of fat that can be loaded with drugs and injected into patients. Because they're similar to the fatty membrane that surrounds all cells, they sneak by the body's defenses. The fat layer keeps the drugs from spreading all over healthy cells and holds them safely inside the bubble until it reaches the disease site. Then, if designed properly, the liposomes self-destruct and release the drug where it does the most good — and the least harm.
Nanotechnologists have now gone one step further. Instead of just copying whatever they find in nature, scientists are building their own parts from scratch. First, a Japanese scientist showed that the enzyme ATP Synthase was a biological motor. Its central shaft rotates clockwise when making ATP, but rotates in the reverse direction when using up ATP. For American scientists Devens Gust and Thomas and Ana Moore, this was a unique opportunity. They had invented an artificial “chloroplast” by embedding bacterial photosynthesis reaction center molecules into a liposome. It harvested light energy, but the energy wasn't put to any practical use — until they added ATP Synthase to their system. Now, the collected light energy is passed on to ATP Synthase, causing it to spin and create ATP.
This was perfect for another scientist, Carl Montemagno. by fusing tiny metal bars to the rotating shaft of ATP Synthase, he had created a nanodevice whose blades would spin when he added ATP to it. But adding ATP wasn't practical. So he teamed up with Gust and the Moores, mixed his nanodevice with their ATP-producing liposomes, and showed that they could make the blades spin just by shining a light on them!
That's not all. Viola Vogel invented a nano-scale “conveyor belt” using a collection of molecular motors lined up all in a row. When a tiny tube is placed on top of the nearest motor and ATP is added, the motors rotate, passing the tube off all the way down the line.
Gust is also working on turning his liposomes into tiny refineries that could someday make gasoline from sunlight and carbon dioxide. Right now, they make only simple compounds, but Gust has high hopes for his liposomes.
In the early days, molecular manufacturing was considered science fiction. Few believed that microscopic machines would someday provide everything we could possibly need or want (think replicators in Star Trek). At that time, the tiny tools required to build such machines hadn't even been invented yet! But with nature's help, nanotechnology these days is looking a lot more like science than science fiction.
- amino acid: Any of a group of chemical compounds containing carbon, hydrogen, oxygen, and nitrogen that living organisms need to make protein.
- bacteria: Tiny one-celled organisms. Some bacteria help digest food; other bacteria cause diseases.
- gene: A short segment of DNA that determines an organism, and it's traits.
- proton: A particle in the nucleus of an atom that has a positive charge.
- Nanotechnologies are designed to accomplish a specific task in a specific way. Why might a nanotechnology that is designed to repair a neuron not be able to repair a muscle cell? Write a sentence or two explaining your answer.