Can living cells be produced in laboratories?
We will not seek an answer to the question, What is life? It is not possible to end or summarize in a few pages the philosophical and scientific discussions about the true nature of life that have taken place for centuries. We will base our discussion on the differentiation of living and nonliving things biologically, the differences between them and the factors that maintain these differences.
All of the living things consist of nonliving molecules. When we examine the compounds in the living things one by one we see that they are subject to the same laws as the other nonliving chemical compounds. However, when we compare the living things and the nonliving things we see that there are important differences between them.
The most important difference between the living things and the nonliving things is that they reproduce and ensure the continuation of a generation similar to them. During reproduction all of the characteristics of the species are maintained throughout generations in the giant molecules called DNA: For instance; some bacteria reached today without undergoing any changes for millions of years. All of the characteristics of a living thing are written in DNA molecules. While human beings hardly keep what they hve written on stones and metals, the codes written on the DNA of a bacterium have remained unchanged for millions of years. Even a smallest living thing has continued its generation by reproduction whereas nobody has seen a mountain give birth to another mountain.
Living things have a very rich and sophisticated structure in terms of chemical compounds. For instance, there are 5000 different compounds in the cell of an Escherichia coli, which is a very simple bacterium and weighs only 1/500 000 000 gram. 3000 of them are proteins, about 1000 of them are nucleic acids and the rest are fats and small compounds. Although the protein molecules in E. coli do the same tasks, they are not the same as the proteins in human beings and other living things. Each species has various protein and nucleic acid molecules peculiar to themselves. It is estimated that there are about 1 trillion different proteins and about ten billion different nucleic acids in the species of all living things. These proteins and nucleic acids are big molecules whose molecular weights are equal to the weights 5-10 thousand to a few million times the weight of a hydrogen atom.
Another extraordinary characteristic in living things is that these various and numerous molecules are made of simple things and in a very short time. Lets give the example of E. coli again: This bacterium can reproduce in a medium which contains only water (H2O), ammonium ion (NH4) and glucose (C6H12O6). Each E. coli cell is divided in less than twenty minutes and two E. coli cells are formed. Either cell is the same as the other. That is, in twenty minutes, 500 different molecules out of three simple compounds like water, ammonium ion and glucose are produced altogether and in necessary amounts. The production of molecules which take place in an incredible pace shows that things that happen in living things are so complex that they cannot be compared with those in nonliving things.
We used E. coli bacterium, which has a very simple structure and which consists of only one cell, as an example. If we consider that there are trillions of cells in human beings and other living things and also the difference of cells and organs, the complexity indicates a point that our mind and imagination cannot reach.
A question like the following arises: Since the actions of molecules can be explained by chemical and physical principles and some interventions on the activities of cells can be done and so many things are known about the living cell, can a living cell or a virus be produced by chemists in laboratories?
Our answer to this question is no. Before we explain why we think so, it will be appropriate to make some explanations about the structural characteristics of the DNA and protein molecules which have very important roles in living cell structures.
DNA (Deoxyribonucleic Acid) molecules function as nuclei in all living things, from viruses and simplest bacteria to organisms with highest structures. That is, they carry all the information about that living thing. That information is present in DNA as codes and it is transcribed to the proteins by RNA (ribonucleic acid) molecules. The codes in DNA molecules are formed by various arrangements of different compounds (adenine, guanine, cytosine and thymine symbolized as A, G, S and T respectively). If we have a look at the variety of proteins in the E. coli bacterium, we can guess how long the DNA molecules can be in living things.
2000 pages are necessary in order to express the DNA base arrangements of an E. coli bacterium. For a human beings arrangements about one million pages are needed. Today, it is not possible to produce even a DNA chain with a length of one tenth of a page in laboratories. What is more a DNA molecule alone is neither a virus nor a living cell. The presence of proteins, which are extraordinary compounds that can enter into all kinds of forms, is necessary in the organisms. When we consider all of the proteins present in plants, animals and bacteria together, we see that the following vital functions are carried out by proteins:
1- All of the chemical reactions in the cell are carried out by catalysts that are called enzymes and that are completely proteins. The necessities of the living things are arranged perfectly thanks to these enzymes like the arrangement of a cars speed by the accelerator.
2- The cells in the nail, skin, horn and the hairs that have a protective function are all in the structure of proteins.
3- The compounds that protect the living things from harmful agents like microbes and viruses that come from outside and that are named as immunity are antibodies which are also proteins. They recognize the things that do not belong to that living thing and eliminate them.
4- For instance, most carrying functions are implemented by some proteins like oxygen-carrying hemoglobin.
5- The input output traffic between the cell and the outside are carried out by proteins located in the cell membranes. That is, what is necessary are accepted in and the wastes and extra materials are taken out in a harmony.
6- The formation and transmission of the stimuli in the nerves are carried out by special proteins.
7- Some of the hormones that have significant roles in directing the body of the living thing like an orchestra are in the structure of proteins.
The researches that are done show that more functions can be added to the functions listed above. Now lets have a look at the complex structure of this extraordinary compound:
All of the proteins of the living things in the world consist of the arrangements of the 20 kinds of amino acids in different orders and proportions. Although the proteins in the species of the living things carry out the same function, they have different structures. Therefore when all of the species of living things are taken into consideration, it will be seen that there are more than one hundred billion kinds of proteins. As volumes of books can be written expressing different meanings with 26 letters of the alphabet, similarly billions of vital functions are arranged to be carried out by giant molecules formed by 20 kinds of compounds. We say giant molecules because except some hormones, the smallest proteins have at least 100 amino acids. Naturally the protein chains that are formed by combining so many amino acids cannot maintain the structures of chains in the cell and are folded in three-dimensional shapes by being twisted on each other.
Thus a protein can carry out its function in a living thing with its three-dimensional shape. Only a few of the protein structures that proteins can have out of billions of different three- dimensional structures can carry out functions. For instance a protein with 100 amino acids can have 1047 (a number with 47 zeros after 1) different three-dimensional structure. It is impossible to guess which one will function. Therefore it is not possible to tell how the arrangement of amino acids should be in a protein to carry out a certain function.
When we consider some of the above-mentioned characteristics of DNA and protein molecules that are indispensable in the life of a cell, we will see the reasons why we answered the question about the production of a living cell as no. If human beings are not capable of producing the molecules that a virus or a cell contains, it will definitely be impossible to synthesize them in a laboratory.
Lets suppose that technology advanced more and human beings realized these syntheses one day. It could not be a proof that life started coincidentally. An outcome that can take place after years and with the accumulation of the knowledge of millions of scientists can only be an indication of an endless ilm (knowledge, science).
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