Scientists in Spain have created artificial cells that move up a chemical gradient all by themselves.
This process is called "chemotaxis", it is ubiquitous in nature. Bacteria use it to find food, white blood cells use it to find sites of infection, and sperm cells use it to find the egg.
The artificial cells in this experiment were created from scratch, they are little more than micelles, made of a phosphatidyl lipid bilayer with some enzymes inside. The physical question is, what forces are in play to move the cell up a concentration gradient? How do the cells "swim" up a gradient?
Obviously, such directional propulsion requires a breaking of symmetry. If all the forces are symmetric, the cell won't move. The force has to be asymmetric in the direction of motion, essentially "pushing" the cell up the gradient.
To accomplish this, the scientists first created symmetric cells with some digestive machinery inside, a glucose oxidase enzyme to break up glucose molecules. Then they put the cells in a glucose solution, which has no effect because the cell membrane is not permeable to glucose.
Next the scientists created an asymmetry by inserting a single hemolysin channel into each cell. Hemolysin is a large molecule with 7 identical subunits that spontaneously self assemble to form a "pore" inside the lipid bilayer, a channel through which glucose can move.
Once the channel was in place, the cells first aligned themselves along the gradient, then began to move in the direction of increasing concentration.
The mechanism causing these forces is entirely physical: the disappearance of glucose from the front of the cell causes water to flow from back to front around the outside of the cell, creating an osmotic pressure. The cells then simply "ride the gradient".
Chemotaxis is "the" simplest propulsion mechanism, it doesn't use flagella or microtubules or actin-myosin motors. It simply takes advantage of the universal laws of physics.
This process is called "chemotaxis", it is ubiquitous in nature. Bacteria use it to find food, white blood cells use it to find sites of infection, and sperm cells use it to find the egg.
The artificial cells in this experiment were created from scratch, they are little more than micelles, made of a phosphatidyl lipid bilayer with some enzymes inside. The physical question is, what forces are in play to move the cell up a concentration gradient? How do the cells "swim" up a gradient?
Obviously, such directional propulsion requires a breaking of symmetry. If all the forces are symmetric, the cell won't move. The force has to be asymmetric in the direction of motion, essentially "pushing" the cell up the gradient.
To accomplish this, the scientists first created symmetric cells with some digestive machinery inside, a glucose oxidase enzyme to break up glucose molecules. Then they put the cells in a glucose solution, which has no effect because the cell membrane is not permeable to glucose.
Next the scientists created an asymmetry by inserting a single hemolysin channel into each cell. Hemolysin is a large molecule with 7 identical subunits that spontaneously self assemble to form a "pore" inside the lipid bilayer, a channel through which glucose can move.
Once the channel was in place, the cells first aligned themselves along the gradient, then began to move in the direction of increasing concentration.
The mechanism causing these forces is entirely physical: the disappearance of glucose from the front of the cell causes water to flow from back to front around the outside of the cell, creating an osmotic pressure. The cells then simply "ride the gradient".
Chemotaxis is "the" simplest propulsion mechanism, it doesn't use flagella or microtubules or actin-myosin motors. It simply takes advantage of the universal laws of physics.
