The receptor stretched the length of the ship and was irregular in outline, as though it were embracing a pattern of bulges along the plastic hull. The hull was smooth and featureless to the eye, of course, but Morrison was quite certain that there was an electric field that bulged in just the locations where the hydroxyl groups would be in the glucopyranose structure, the bulges taking on just the shapes they would in the natural molecule.
Morrison looked out again. The receptor virtually blanked out vision on the side of the ship along which it lay. If he looked beyond the receptor, however, he could see a farther stretch of the neuron's surface, seemingly without end, for it vanished beyond the reach of the ship's light.
The neuronic surface seemed to be heaving slightly and he could see greater detail. Among the regular domes of the rank and file of phospholipid molecules, he caught occasional glimpses of an irregular mass, which he guessed to be a protein molecule that ran through the thickness of the cell membrane. It was to these molecules that the receptors were attached, which did not surprise Morrison. He knew that the receptors must be peptides - chains of amino acids. They were part of the thread of a protein backbone, sticking outward, each different receptor made up of different amino acids in a specific order so designed as to possess an electric field pattern matching (in opposing attractions and physical shape) that of the molecule it was designed to pick up.
Then, even as he watched, it seemed to him that the receptors were moving toward him. He could see them now in greater numbers and could also see that those numbers were still increasing. The receptors and the protein molecules to which they were attached seemed to be swimming through the phospholipid molecules (with a film of cholesterol molecules underneath, Morrison knew), which opened before and closed behind.
"Something's happening," said Morrison as he felt the ship's own motion through the tiny drag of inertia that remained to them at their thoroughly negligible mass.
Kone said, "The surface is gathering us in."
Dezhnev nodded. "It looks like its doing this." He held up his thick and callused hand, cupping it.
"Exactly," said Konev. "It will invaginate, make a deeper and deeper cup, narrowing the neck and finally closing it, and we will be inside the cell." He seemed quite calm about it.
So was Morrison. They wanted to be inside the cell and this was the way it was done.
The receptors continued coming together, alongside each one of them some molecule - some real molecule - and in among them the feigning molecule of the ship. The cell's surface, like Dezhnev's cupped hand, closed upon them entirely and drew them in.
"Now what?" said Dezhnev.
"We're in a vesicle inside the cell," said Kaliinin. "It will grow more acid and the receptor will then detach itself from us. It and all the receptors will then return to the cell membrane."
"And we?" persisted Dezhnev.
"Since we are recognized by our electric field as a glucose molecule," said Kaliinin, "the cell will try to metabolize us - break us up into smaller fragments and extract energy from us."
Even as she spoke, the peptide receptor fell away, uncoiling.
"Is that a good idea, having it metabolize us?" asked Dezhnev.
"It won't," said Morrison. "We'll be attached to an appropriate enzyme molecule which will find that we don't react as expected. We won't take on a phosphate group, so it will be helpless and will probably release us. We're not really a glucose molecule."
"But if the enzyme molecule releases us, won't another enzyme molecule of the same type attach itself to us and try again - and so on indefinitely."
"Now that you mention it," said Morrison, rubbing his chin and absently noticing the bristles grown since his morning shave, "it may be that the first molecules won't let us go, I suppose, if we won't do the expected."
"A fine situation," said Dezhnev indignantly, slipping into his local dialect of Russian, as he always seemed to do when excited, and which Morrison always had a bit of difficulty in following. "The best we can expect is that an enzyme molecule either holds us forever all by himself or holds us forever in a relay race as we pass from one enzyme to another indefinitely. - My father used to say: 'To be saved from the jaws of a wolf by a hungry bear is no great cause for gratitude.'"
"Please notice," said Kaliinin, "that no enzyme molecule has attached itself to us."
"Why is that?" asked Morrison, who had, indeed, noticed that.
"Because of a slight change in electric charge pattern. We had to mimic a glucose molecule to get into the cell, but once in, we don't have to be one anymore. In fact, we must mimic something else."
Boranova leaned forward. "Won't any molecule we mimic be liable to metabolic change, Sophia?"
"Actually, no, Natalya," said Kaliinin. "Glucose - or any other simple sugar in the body - belongs to a certain molecular configuration, so that we call it D-glucose. I've simply altered the pattern to its mirror image. We have become L-glucose and there isn't an enzyme that will touch us now, any more than any of us are likely to put a right shoe on a left foot. - Now we can move about freely."
The vesicle which had formed on their introduction to the cellular interior had broken up and Morrison gave up as hopeless any attempt to follow what was going on. Fragments around him were enveloped by much larger enzyme molecules that seemed to embrace them and then relax. Presumably, an altered victim of the enzymatic squeeze was set free to be embraced again by another enzyme.
It was all happening at once and, Morrison knew, this was only the anaerobic portion of the process (in which no molecular oxygen was used.) It would end by breaking up the glucose molecule, with its six carbon atoms, into two three-carbon fragments.
A little energy would be produced in this fashion and the fragments would be shunted to the mitochondria for the completion of the process with the use of oxygen; a process in which the universal energy-transfer molecule, adenosine triphosphate (or ATP, for short) would be invested in order to get things started and, in the end, be produced once more in quantities substantially greater than the investment.
Morrison felt the urge to drop everything and to find a way into a mitochondrion, the small energy factory of the cell. After all, the fine details of mitochondrial processes had still not been worked out - but then he pulled away almost angrily at the thought. The skeptic waves came first. He shouted that to himself, as though trying to force a realization of priorities onto an overly curious brain that was threatening to diffuse its interests.
Apparently, the same thought occurred to Konev, for he said, "We're finally inside the neuron, Albert. Let's not be tourists. What do you find in the way of skeptic waves now?"
Chapter 14. Axon
Those who say "A penny for your thoughts" are usually being overgenerous.
Morrison bristled at Konev's order. (It had definitely been that.)
He indicated his resentment by refusing to respond at all for a while. He continued to stare out into the interior of the neuron and could distinguish nothing he recognized. He could see fibers, convoluted plates, hulks of uncertain size and of no clear shape. What's more, he had a strong feeling that there was a skeletal presence in the cell that held the larger objects - the organelles - in place, but that the ship was slipping past it all too quickly, as though it were in a river racing downstream. The feeling of motion was far stronger here than in the bloodstream, for though there were small objects (debris?) that moved along with them, there were larger objects that apparently remained in place and that they passed rapidly.