Cells of living things

Cells living beings - libraries with thousands of pages of information

In 1953, two molecular biologists, James Watson and Francis Crick, made public a discovery of major importance for understanding life: the double helix structure of DNA. The DNA molecule, found in the nucleus of most cells, contains coded information, making cells true living libraries.

What are cells?

Cells are the basic structural, functional and genetic units of all living organisms. The cell was discovered by Robert Hooke. It is the smallest unit of life that can be classified as a living thing and is often referred to as the 'building block of life'. Some organisms are simpler, such as most bacteria, and are called unicellular because they consist of a single cell. Other organisms are more complex, such as humans, who are multicellular entities.

The word cell comes from the Latin term cellwhich means, "small room". This word, meaning the smallest structure of biological life, was given by the English scientist Robert Hooke, who excelled as an astronomer and physicist. Hooke anticipated some of the most important discoveries and inventions of his time. He invented and perfected many instruments for observation and measurement (telescopes, thermometers, microscopes). With the Gregorian telescope, Hooke first observed plant cells. In a book he published in 1665, Hooke uses the term 'cell', comparing the cork cells he saw through his microscope to the small living quarters of monks.

Cells contain information

If we were to ask how a tree develops from a seed, or how a human develops from a fertilised egg, or how we inherited certain personality traits, the answers to all these questions are related to the information contained in cells, specifically in the DNA of the cell.

Deoxyribonucleic acid, or DNA for short, is a nucleic acid made up of complex organic molecules. DNA is found in every cell of living things and is essential to the identity of that organism.

DNA is the genetic material of the body and is the main chemical constituent of chromosomes. Each chromosome contains a DNA molecule, which supports the control of cellular activities and the transmission of hereditary traits.

The DNA molecule is very long and consists of two strands twisted around each other, forming a double helix. The sequence of structures on the DNA strands form a special code, the genetic code, which determines how the body looks, grows and functions.

On one of the strands is the information that coordinates protein synthesis by enzymes. Proteins are what control cellular activity. During cell division, enzymes separate the two strands and synthesise two new strands in front of the old ones. This forms two new DNA molecules, identical to the original one. These two new DNA molecules are each destined for another daughter cell. This phenomenon, called DNA replication, ensures genetic identity during cell multiplication.

The DNA molecule encodes not only the information needed for self-replication, but also the information needed to build a whole living organism. The specific blueprints for a bee, a fish, a nightingale or a human are embedded in the DNA structure of that organism in a molecular code billions of letters long.

DNA looks like long, twisted ladders. In the human genome - the totality of our genetic material - the ladders have about three billion chemical 'rungs'. Scientists call these rungs base pairs, because each rung is made up of two chemicals. In total, there are four such substances, called adenine, thymine, cytosine and guanine. These are coded using their initials: A, T, C and G. The DNA helix has a double helical shape, a so-called 'double helix'. For each rung of the 'ladder' two of the four nitrogenous bases coexist and we always have pairs of A and T or G and C, so if one side of one rung of the ladder is known, automatically the other is also known. Step by step and for the price of 3 billion letters, the "formula", the "code" necessary for the emergence of a human being, is thus revealed.

The existence of this tiny code, written molecule by molecule inside each cell, is in itself an epochal discovery. But since the 1960s, scientists have done even more, 'reading' or, in other words, decoding this code, i.e. examining it letter by letter and recording or memorising in various forms both the human genome and the genetic codes of other living things.

Identification based on DNA evidence

The DNA molecule can be likened to a 'twisted or spiral ladder'. The rungs of this ladder consist of the four molecules: adenine, thymine, cytosine and guanine. These four molecules represent the 'letters' that make up the genetic code. Step by step, these letters make up the formulas that define every living organism. The formula associated with a human being - the human genome - contains over 3 billion letters.

On a genetic level we humans are all almost identical. Although the differences between human genes are insignificant compared to the size of the human genome, modern DNA decoding technologies can detect and identify these differences. The uniqueness of each human's genetic code can be a feature that makes the decoding procedure a very useful tool in a variety of applications, from DNA-based identification and paternity establishment to forensic medicine and criminal investigations.

Specialists in this field can recover and extract DNA samples from the smallest human tissue samples. Once a quantitatively sufficient and qualitatively appropriate sample has been obtained, a multi-step process called 'DNA electrophoresis' begins, a procedure that reveals even the smallest molecular differences within a genetic sequence.

At first, specialised enzymes are used to chemically separate the DNA 'strands' at specific positions in the genetic sequence structure. This process results in DNA fragments of different sizes for different individuals. These DNA fragments are immersed in a special gel to which an electric current is applied. DNA fragments of different sizes move through the gel at different speeds when the electric current is applied. The result is a specific distribution of DNA in the colloidal solution, from which the 'owner' of the DNA can be identified. The resulting pattern is a so-called 'DNA fingerprint', unique to each individual.

The information in a bacterial cell would fill a thousand-page book

Information, whether it is images, sounds or words, can be stored and processed in many ways. Living cells store and process their information chemically, the basic compound being DNA. It is transmitted during cell division and reproduction, which are essential capabilities for life.

DNA can be compared to a series of recipes, each recipe involving processes that take place in successive steps. In turn, the steps are described in precise terms. But instead of a cake or a cake, the end result may be, for example, a tomato or a horse.

Genetic information is stored for as long as necessary to replace ageing or diseased cells with new, healthy ones, or to pass on certain traits to offspring.

DNA contains a huge amount of information. German researcher Bernd-Olaf Küppers said of the bacterium, which is one of the smallest organisms: "Transcribed into human language, the molecular text describing the formation of the bacterial cell would fill a book of about a thousand pages". David Deamer, professor of chemistry, rightly said: "Even the simplest life form is astonishingly complex!". But what about the human genome? "It would fill a library with several thousand volumes," said researcher Küppers.

The genetic code is written in a way that we can understand

Calling the writing in DNA "molecular-genetic language" is not "mere metaphor", Küppers said. He added: "Like human language, molecular-genetic language has a syntactic dimension." In other words, DNA has a "grammar" or set of rules, which strictly regulates how instructions are composed and followed.

"The 'words' and 'sentences' in DNA make up different 'recipes' that determine how proteins and other substances that make up the different types of cells in the body are produced. For example, one 'recipe' may command the making of bone cells, another the making of muscle, nerve or skin cells.

Biologist Matt Ridley wrote: "The DNA strand is information, a message written in a code of chemicals, one for each letter. Although it sounds too good to be true, the code turns out to be written in a way we can understand."

How did the information get into the DNA?

When the most sophisticated code ever known to man, the chemical code of life, was discovered, many scientists wondered, "How did the information get there?"

It is remarkable that there have been scientists, such as Dr Gene Hwang and Professor Yan-Der Hsuuw, who have given common sense explanations.

Dr. Gene Hwang was a professor of mathematics at National Chung Cheng University in Taiwan. He is also Professor Emeritus at Cornell University (USA), where he has taught and researched probability and statistics. He studies the mathematical basis of genetics.

In an interview he gave to a magazine, he said: "The more I thought about the origin of life, the more I became convinced that the first form of life must have been very complex. For example, it must have had the ability to reproduce, which requires genetic information and a mechanism to replicate that information exactly. Also, even the simplest living cell needs molecular machinery to build all the parts of a new cell, as well as means to harness and direct energy. How could such complex mechanisms randomly form from non-living matter? As a mathematician, I could not accept such a hypothesis. It demands too much from random processes. In recent years I have provided mathematical support for scientists studying gene function. The study of genetics provides a clearer understanding of the mechanisms of life, an understanding that fills me with admiration for God's wisdom."

Another scientist, Professor Yan-Der Hsuuw, who is the Director of the Embryo Research Centre in the Faculty of Science and Technology at National Pingtung University in Taiwan, said of cell division and cell specialisation: "A certain type of cell must be produced in a certain order and in a certain place. First, they group together to form tissues, which in turn group together to form organs and limbs. No engineer in the world could ever write the instructions for such a process! However, the instructions for embryo development are masterfully written in DNA. When I think of the beauty of the whole process, I am even more convinced that life was created by God."