By John Ogunlela
As bricks form a building, all humans and indeed big organisms – plants animals alike – are made up of microscopic structures called cells. Cells are the building blocks of our bones and muscles, hairs and even a good part of our blood. The number of cells it takes to build a human being is estimated to be about 30 trillion. Hairs and nails are dead cells and they are actually the same in structure called keratin.
Take it under the microscope and a cell looks rather unimpressive. It is a simple frail thing, somewhat round in an irregular manner but when it is appropriately stained; a few curious things inside of it become visible. There is an unmistakable, prominently dark patch within the cell called the nucleus and it looks like the most important of all the little blotches and thin lines within the cell. This region, this sack rather, contains some of the most wonderful things known to man. We call them ‘some of the most wonderful things’ just not to startle you. They are definitely the things you will never be able to define without your biggest superlatives – as we shall see.
The wonder structures hide from probing eyes until they are nudged by a special timing mechanism to divide and then they thicken into view. At the beginning, they look like short threads but gradually, they get thicker and align in pairs. A point of joining is defined and the pair forms a rough letter ‘H’ – which seem to some rather as an X. The point where they come together – the dash of the ‘H’ is called a centromere and this point hold both sides in place and then wonderful things start to happen.
There are 44 regular chromosomes in human beings along with two special chromosomes – the X and Y chromosomes – which decide whether you will be a man or a woman – 46 in all which pair up into 23. (In genetics, this is referred to with an ‘n’ prefix, they’ll say, in referring to the number of chromosomes in the particular organism, that 2n= so and so. In humans, 2n=23; it is six in mosquitoes, 2n=20 in maize and 30 in the giraffe.
Chromosomes reveal their miracles upon further probing. Half of their mass is some sort of proteins to hold them together while the other half are strings of highly compressed polymers, mostly of a special molecule called deoxyribonucleic acid or DNA. They are accompanied by their simpler cousins, the RNA or ribonucleic acid. The deoxy – type is chemically made up of two strands of while the other type is a single strand.
But strands of what? And here is where the big story begins, the big story of the miracle of life and the bewildering complexity that appears in elegant simplicity from which life itself comes and by which it is sustained. It is a bit detailed but is worth taking some pains with for understanding it is understanding the basis of living and diversity among people, animals, plants by their billions.
The DNA molecule is a giant molecule – the type called polymers in chemistry. A polymer is a molecule formed from a repeat of a basic smaller unit, joined in a chain. Certain simple gases, for example are compressed and they form long chains of the same basic chemical and this transforms them from being gas into plastic! DNA is a polymer of what we call nucleotides. Nucleotide in turn is a big molecule with three parts. While the water molecule is simple, consisting of two hydrogen atoms and one oxygen atom, the nucleotide consists of about 25 atoms of nitrogen, oxygen, phosphorus all arranged in three groups in a unique way. It is a lot of chemistry, but we should just say they are arranged into the following groups:
- A Phosphate group;
- a Ribose sugar group and
3; a NITROGENOUS BASE, which is the crucial element of all.
The first two are always the same while the third is not. That Number 3, nitrogenous base, comes in four or better still, five different forms named ADENINE, CYTOSINE, GUANINE AND TYMINE in the DNA. (The guanine is replaced with URACIL in RNA). Now here is the core of the thing: THE SEQUENCE OF THESE FOUR OR FIVE BASES IS THE CODE CONTAINING ALL THE INFORMATION OR INSTRUCTIONS FOR MAKING THE PARTICULAR ORGANISM OR THE INDIVIDUAL. THE PATTERN OF THEIR ORDER ARE THE COMPLETE INSTRUCTION MANUAL FOR MAKING AND MAINTAINING THE LIFE OF THE PARTICULAR ORGANISM.
If we take a single cell from your body – something so tiny you won’t even feel a thing, your DNA can be fully read off from the chromosomes it contains and we can know your gender, trace your ancestry, determine the diseases you are susceptible to and in fact, make a thousand, even a million or billion copies of you!
The sequence of the nucleotide bases we described earlier are the codes that instruct your body how to develop, fight diseases, respond to drugs, stress, in short, it is the control room of your life in ways you can imagine or not imagine. It also contains all the information needed for making half of your children – your spouse will provide the remaining half. If Cytosine follows Guanine and Adenine is next, the implication is vastly different from if Adenine stays in the middle, for example. The exact sequence or arrangement of these bases in a specified number is called a gene. That is, a complete set of instructions defining a feature of the organism. As we said earlier about the DNA, it comes in two strands which form into something like a twisted ladder and the bases hold one another across the space separating the two legs of the ladder. This is called pairing and the human genome contains 3.2 billion such pairs. The project to count this was commissioned in 1990 and was completed thirteen years after.
Next is the identity of the combination of those pairs that make up an exact set of a specific instruction on how to make what – or the gene of the human being. In all, there are 20,000-25,000 of such short code sets; in other words, a human being is made up of 20,000-25,000 genes. If scientists can understand the exact sequence of the base pairs that make each of those genes and find means to rearrange them in safe and precise order, virtually any type of humans – or plant or animals whose gene structure and base paring have been so fully understood, can be made.
All cells in the body contain exactly the same genes but they function differently because only specific portions of the codes in their DNA is activated so that they appear and behave in different ways. This is why brain cells act differently from blood cells. This is how DNA basically causes our bodies to form and maintain itself.
The second duty of genes is that they help to create a new individual from their parents. The process of reproduction has designed a clever way to make this happen. Remember we said the cells in the human body have 46 chromosomes in all, right? We need to re-examine that as we look at the finer points of how babies are made.
All body cells have 46 chromosomes except the cells formed in the special parts of the male testicles and the female ovaries in a process called gametogenesis – {gamete: genesis or beginning}. In that unique process, the cells divide in a special way so that they end up with half the normal number of chromosomes. This is meiosis and its effect is obvious – it allows both genders to bring only half of the baby to be born. The advantage of this is in what biologists call the advantage of diversity. The offspring is stronger as the genetic differences between the parents get bigger. Diversity strengthens, uniformity weakens.
Many interesting things happen in this process in the name of crossovers and linkages to further deepen diversity so that the offspring will be better than its parents in the ever increasing process of purification and reinforcement of life.
So the sperm cell descends by their millions – about 300,000 per emission in humans and the woman readies usually just one egg. The egg is one of the biggest cells known – so big you can see it with your naked eyes as a tiny speck while the sperm is hopelessly little and invisible until it is under the microscope. The egg is thirty times bigger than the sperm cells. (Your instincts are correct – in the end, the woman contributes more genes to making the baby than the man. But that is a different issue for another day. For now, we stick to the genes in the nucleus of the cell 23 in both the egg and the sperm cells).
The sperms wiggle their tails and swirl all over the egg, one of them manages to dissolve the skin of the egg with a chemical in its cap and he makes it inside. At that moment, the egg hardens up in a chemical reaction so that no other sperm cell can come in and the rest 299,999 sperm cells locked out die mere death out there in the cold.
The successful sperm cell promptly mixes his 23 chromosomes into the egg and along with the 23 already present in the egg, the standard 46 number of chromosomes is restored in the newly formed special cell called a zygote. The zygote divides into two and then into four, eight, 16, 32 on and on in the process of forming a new complete human. By Day 5, there is now a tiny bundle of cells called a blastula and until the cells are up to 60-150, they carry a strange quality – if they are separated, each of them can grow up to full individual beings of their own right. They are the STEM CELLS and in this sense, they are said to be pluripotent. The act of actually separating cells at this blastula stage to create separate new organism is called cloning.
All of the babies produced that way have nearly 100% genetic similarity. (Another person may not add the word, ‘nearly’, for reasons of the disparity in the size of the egg and the sperm. I will explain that in the comments). Identical twins are therefore actual clones as they are formed when the zygote divides into two and the two cells drift apart. Since they carry basically the same genetic information, they are the same person now duplicated.
Once the cells grow past the 150 mark however, they lose their pluripotency. They have differentiated and become totipotent – they cannot grow into individual people anymore but will grow to form the different tissues and organs of the body. The burden of stem cell research is the idea that people may be able to get medical help in some special circumstances under this special science. ACCORDING TO THE MAYO CLINIC, “STEM CELLS CAN BE GUIDED INTO BECOMING SPECIFIC CELLS THAT CAN BE USED TO REGENERATE AND REPAIR DISEASED OR DAMAGED TISSUES IN PEOPLE. PEOPLE WHO MIGHT BENEFIT FROM STEM CELL THERAPIES INCLUDE THOSE WITH SPINAL CORD INJURIES, TYPE 1 DIABETES, PARKINSON’S DISEASE, AMYOTROPHIC LATERAL SCLEROSIS, ALZHEIMER’S DISEASE, HEART DISEASE, STROKE, BURNS, CANCER AND OSTEOARTHRITIS. STEM CELLS MAY HAVE THE POTENTIAL TO BE GROWN TO BECOME NEW TISSUE FOR USE IN TRANSPLANT AND REGENERATIVE MEDICINE.”
The idea here will be clearer when we explain the second type of cloning – cloning using somatic cells or cells with 46 chromosomes which is available everywhere in the body. Somatic cell cloning was the means used to create Dolly the Sheep in 1996 in Scotland. In this amazing leap of science, a cell was taken from the mammary glands of the animal. The nucleus was extracted and inserted into another mammary gland cell of another animal which had had its nucleus removed. The new cell (with 46 chromosomes, remember) was induced with an electric shock so that it starts dividing. At the moment is begins to divide, it has transformed from a normal body (that is, somatic) cell and had started behaving like a zygotic cell that is made from the fusion of sperm and egg as we saw earlier! This is the wonderful miracle of somatic cloning – the ability to reproduce an individual completely without the opposite sex.
This cell is now pluripotent and it can be introduced into a ready womb where it will establish as a pregnancy. The baby born is an exact image of the woman that supplies the nucleus that the process began with. That was how Dolly the Sheep was made – she had no father. (The gender of all such asexual or pathenogenetic offspring is female since the process has no access to the Y chromosome that is borne on the sperm cells alone). By the books, a human being can be made through such means and the baby so born will live. The implication of this is as straightforward as it seems – any number of you can be made from a single cell taken from your body.
The medical angle to this is obvious, looking at the Mayo Clinic position above: suppose a person is in need of a new heart and has no donors whose tissue fits. Or, suppose, tissue rejection is really an issue here for various reasons. Scientists are thinking that it could be okay to take a cell from the patient, induce it and then, once the cells begin to differentiate into body parts, carefully separate the tiny cluster that will develop into the heart for harvest and destroy the rest of the tissues. The new heart will be tended and after it has reached the correct size, it will be transplanted into the patience. Since the new heart originates from the patient’s genes, the graft can be expected to take, and there will be no rejection whatsoever.
There is a swirl of ethical questions around this however and understandably so; but as we query its morality, we should also ask for the opinion of the patient and those of their loved ones to obtain a balanced view.
We have established that the sequences of DNA molecules compressed into the chromosomes that inhabit the nucleus of our cells are the genes that define everything about us. A gene is the exact way the four base pairs in the nucleotide follow one another as they are strung on two lines which hold to one another like a twisting ladder. It therefore follows that if we can rearrange that sequence, we can bring about serious changes in the baby that will be born.
This is absolutely true and it is the basis for genetic engineering and it can result in good or ill. Let us assume for example, that the sequence: Guanine-Adenine- Cytosine-Adenine-Thymine-Adenine-Adenine is the code for forming the fingernails. Suppose a scientist unbundles the sperm cell carrying this information and tampers with the Cytosine and changes it to Guanine. Serious coding error is the result and it might mean the fingernails will begin at the bottom of each finger rather than on the tip!
Lets look at a real life example of a gene called TP53. It is a powerful, exceptional and elegant gene that instructs cells to stop dividing. If this gene is missing, cells will keep diving on and on and this is what happens in cancer patients. The gene has been found missing in half cancer patients. (This process where a gene just gets missing occurs when it is cut off from its string on the chromosome and it is called mutation) . Mutation can be caused when reproductive cells are bombarded by high energy electromagnetic radiation or fast moving heavy particles like beta particles, gamma rays, x-rays and high speed neutrons.
They simply knock off DNAs from their mooring and the result is abnormalities in the new born. Codes for making the hands may be missing, or for making the hairs or for making melanin, the pigment, melanin, that gives colour to our skin. TP53 is known by geneticists as the guardian cells and it suppresses runaway growth or cancer, according to Nature International Journal of Science. Genetic engineers and oncologists are trying to see if they can replace missing TP59 gene in cancer patients to effect a perfect cure at the level of the DNA.
We will stop here today and tomorrow, the Part 2 will be posted. That part will deal with how genes are edited, designer babies and answer questions on genetically modified organisms or GMOs. We will also look at the dangers of the practice of editing genes which is why people fear genetically modified foods.
