MadSci Network: Cell Biology

Re: Is it impossible to artificially create sperm or human eggs?

Date: Wed Jan 23 11:07:00 2002
Posted By: Paul Szauter, Staff, Mouse Genome Informatics, The Jackson Laboratory
Area of science: Cell Biology
ID: 1006060583.Cb

You have asked an interesting question. It is hard to answer this, because I 
don't know what material we are allowed to start with, and I'm not sure what 
the intent of your question really is.

Human sperm and eggs are complex, highly differentiated cell types that 
arise from other human cells. Because they only arise from other living 
cells, many people in the history of biological science have wondered 
whether there is anything special about living things that distinguishes 
them from nonliving things. This question can be framed more precisely by 
asking whether there are any processes outside the realm of chemistry and 
physics that explain what is going on in living organisms.

A very limited aspect of this question was addressed in the nineteenth 
century, when it was thought that "organic" chemical compounds were those 
that could only be synthesized by living things, while inorganic compounds 
could be formed from chemical reactions that did not involve living cells. 
In 1828, Friedrich Wohler synthesized urea accidentally while attempting to 
make ammonium cyanate. We now use the term "organic chemistry" to refer to 
the study of carbon-containing compounds. Hundreds of thousands of organic 
compounds have been synthesized without the use of living cells or enzymes, 
showing that there is nothing about chemical synthesis in living cells that 
distinguishes it from chemical synthesis in glassware.

We have learned a great deal about biology in the last half of the twentieth 
century. The mechanism of inheritance has been solved down to the molecular 
details. It is a reasonable summary to say that everything that a cell can 
do is ultimately dictated by the genetic material within the cell. We are 
very close to completing the sequencing of the human genome. This will allow 
us in principle to specify all of the proteins that can be synthesized by a 
human cell. If we understood the function of all of the proteins that are 
encoded by the genome, we could understand everything that a cell could do. 
Are there any processes that happen in living cells that would not be 
immediately apparent from looking at all of the genes?

Many people who have thought carefully about this problem take difficult 
examples of human behavior to try to challenge the idea of physics and 
chemistry explaining living things. If you enjoy literature, poetry, or art, 
you probably don't see them as being entirely explained by physics and 
chemistry. Yet an artist's thoughts, besides being the consequence of his or 
her life experiences, are the product of chemical and electrical activity in 
his or her brain, all of which can ultimately be explained by chemistry and 
physics. This is not to say that we can synthesize art in a test tube, just 
that even though many scientists enjoy art, they do not regard it as having 
a supernatural or nonmaterial origin. The consensus in the life sciences now 
is that there are no new principles in biology that are not ultimately 
explained by chemistry or physics. There are many interesting stories in 
biology, but they rest on chemistry and physics.

This is a sort of digression that really is an attempt to address your 
question. It is possible to chemically synthesize DNA. The longer the 
molecule, the more difficult and expensive the synthesis, but the entire 
human genome could in principle be synthesized once a complete sequence is 
known. This is not enough to make a cell, though, because the protein 
products of some genes regulate the activity of other genes. Differentiated 
cells express a subset of regulatory genes that result in the expression of 
a restricted subset of genes. This is just one example of a complex set of 
gene products that must be present in the cell. The entire array of gene 
products necessary for gene expression must also be present in the right 
amounts. Some of these are complex macromolecular assemblies, such as 
ribosomes. All of the enzymes necessary for metabolism must also be in 
place. In addition, the cell has internal membranes that divide it into 
compartments, such as the nucleus. We can chemically synthesize 
phospholipids, and even form them into membranes, but the real nuclear 
membrane has "pores" made of proteins that are encoded by genes. In your 
question, are we allowed to have genetically-engineered bacteria synthesize 
the proteins, or do we have to do that chemically? In addition, the cell has 
other complex subcomponents like mitochondria, which even have their own 
genome. To make a human cell, we would have to build these as well.

The point of this is that we might in principle be able to synthesize each 
of the components of a human cell, and even put one together, with enough 
knowledge and technical skill. It may seem that accomplishing this would be 
a demonstration of the completeness of our knowledge, but each individual 
piece of knowledge about human cells can be demonstrated and verified in 
experiments that require less than building a human cell from scratch. So 
there is no scientific reason to attempt to construct a human cell by 
chemical synthesis.

The answer to your question therefore is that it might be theoretically 
possible to build a human cell from scratch using only chemical synthesis, 
but that this is an extremely difficult technical feat that has no 
scientific purpose.

For some good background reading on the structure and function of cells, 
please see "The Molecular Biology of the Cell" at:

For definitions of terms in genetics, please see:

Thanks again for an interesting question.


Paul Szauter
Mouse Genome Informatics

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