ugg men boots a new chapter in health and disease
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While it has been known for some time that diet and specific nutrients can affect the gene functions, new research is expected to greatly advance our knowledge of nutrition and health. With the arrival of the first draft of the human genome, a whole new chapter on genetics, health and nutrition will be written. Research in this area has accelerated since the unravelling of genes in humans because scientists can now identify the various ways in which diets and nutrients affect individuals and how our genes are turned on or off by what we eat.
In February 2001 two independent teams of researchers raced against the clock to simultaneously publish their findings in two of the world’s most prestigious journals Nature and Science. The first „rough draft“ of the human genome had been unravelled. This is an achievement nothing short of astonishing when one considers that the complete sequence of the human genome consists of 3.2 billion letters and is so enormous that it can only be published in data bases on the Internet. It has been estimated that it would take more than 75,000 pages of a newspaper just to print the full sequence!
The entire sequence of the human genome is expected to be completed by 2003 yet this will only signal the beginning of increased activities into identifying specific functions and interactions of genes in an effort to unlock the enormous potential of genetic information. Research on the human genome has been painstaking and exacting, requiring an in depth knowledge of cell function and reproduction. The following paragraphs very briefly and simply review current understanding of the structure and function of various aspects of the human genome.
2.1 DNA structure and function
Cells are the fundamental units of all living systems. We are all made up of billions and billions of cells, but each has the information necessary to make a new entire human. This is possible because all of the information and instructions needed to make a human are encoded in a single group of molecules called deoxyribonucleic acid (DNA). DNA is found in the nucleus of the cell. In humans, and all higher species, a DNA molecule consists of two strands of DNA, which wrap around one another to resemble a twisted ladder (Figure 1). The sides of the ladder are made up of sugar and phosphate molecules (deoxyribose) while the rungs consist of chemical compounds called bases.
DNA encodes an information language made up of just 4 letters, which are termed chemically, bases. In the DNA molecule the two strands are mirror images of each other because each base in one strand is matched to a specific partner on the opposite strand. Adenine (A) is paired with thymine (T), and guanine (G) is paired with cytosine (C).
All of the information needed for a cell to function or reproduce is encoded in the sequence of these four bases. This sequence extends for billions of bases along the genome. Every life form on the planet uses this same language and hence, the particular order of the bases adenine, thymine, guanine and cytosine is important because this is what makes a human a human, rather than an earthworm. In other words, it is the sequence of bases that underlies the diversity of organisms. Imagine the possibilities made possible by this biological constant. All organisms use the same language to store all of the information needed to create them. The DNA sequences hold the secret of every life form from bacteria to humans, and science has now decoded these books of life called genomes.
FIGURE 1: Deoxyribonucleic acid (DNA) structure.
A genome consists of the entire DNA sequence of an organism, including, of course, its genes. Genomes vary in size depending on their source. For example, the small genomes from bacteria have approximately 600,000 DNA base pairs (bps). The human genome has about 3 billion base pairs.
While genes get a lot of attention, the actual workhorses are the proteins. Genes carry information to enable the cell to make thousands of proteins. The proteins in turn determine a whole host of features such as what the organism will look like, how well it functions and perhaps even how it behaves.
When a cell needs to use a particular piece of information, the appropriate section of the double stranded DNA molecule is opened like a zipper, and one of the strands is used as a template to synthesise a new molecule called „messenger ribonucleic acid (mRNA)“, by a process called transcription. mRNA is a long single stranded molecule that resembles a comb. It is made up of ribose (a sugar) and phosphate molecules with one of the four chemical bases attached to each ribose chain. The sequence of bases on mRNA but here consisting of uracil, adenine, guanine and cytosine is the same as the section of DNA that was used to create it. mRNA carries the DNA’s message out of the cells‘ nucleus where it can be used to make proteins.
The human genome is enormous. If the DNA molecules in just one human cell were stretched end to end they would be approximately 2 molecules wide and 5 feet long. A 1 mm thick thread of equivalent proportions would be 1000 km long. This DNA is arranged in 23 units or chromosomes, each chromosome occurs as a pair of 2 with one chromosome donated by each parent. In the simplest terms, a gene corresponds to a section of the DNA molecule that codes for a protein. In the human genome the genes are spread throughout the various chromosomes, and although all 3 billion bases of the human are now known,
scientists do not yet know precisely all the genes. This information is the basis of ongoing research.
Research using the knowledge from the Human Genome Project will ultimately enable scientists to understand the functions of human genes and the laws that regulate how they are turned on and off. This knowledge in turn will provide them with information on how genes and nutrients interact and the effect of individual genetic differences on diet, nutrition and health. For example, the actual way in which some nutrients such as those from milk, fruits and vegetables, produce desirable changes in metabolism is largely unknown, which is why dietary recommendations are still so frustratingly vague. The study of nutrigenomics can help to identify these effects and help to understand why certain ingredients and foods are of benefit to health. Similarly, the genetic basis behind the differences in how some people respond to particular foods and nutrients can be identified and used to recommend foods and diets that are most beneficial for each individual.
Nutrigenomics will also help to provide new information for developing more accurate biomarkers (indicators) to detect various diseases much earlier and identify the genes that can be targeted by nutritional intervention to prevent them.
4. POTENTIAL BENEFITS OF RESEARCH INTO GENES
Research into the functions of genes will help to identify just how diet affects gene and protein functions and why individuals vary in their response to nutrients and diets. We all know that even when people are eating the same diets, some will become overweight, some develop heart disease and some develop allergies while others do not. Wouldn’t it be wonderful to know why? This knowledge can help in the development of even more nutritious foods. Specific foods with beneficial properties (functional foods) could then be developed to help optimise the health of each individual according to its genes. This may seem far in the future, but we already eat foods according to our genetic differences. Women know that they need to eat foods with more iron than men do and the difference in iron requirement is due to their genetic difference. As we understand more about the other differences between men and women and between all of us, we can provide the knowledge to individuals so that they can choose foods that are most appropriate for them. For example, knowing how individuals develop allergies would lead to foods not simply to avoid allergens but foods that prevent people from even developing allergies in the first place.
One of the most intriguing areas of research, that will eventually help everyone, is understanding the processes of ageing and diseases of the elderly. Scientists have found that about half of the diseases that come with ageing have a genetic component. Substances in foods can influence some of these functions so the potential exists to identify dietary ways to delay ageing or to promote healthy ageing.
Genetic research can help in identifying ways to develop functional foods to deliver benefits that we hadn’t even thought of until recently. One example is the role of certain bacteria in intestinal and overall health. Imagine eating bacteria to make you feel better! Genetic research will help to understand why certain bacteria (for example lactic acid bacteria), have beneficial properties such as enhancing immune functions, assisting digestion and improving intestinal comfort. A greater knowledge of the types of beneficial bacteria and the way in which they act in the digestive tract to provide protection from other bacteria can also improve our ability to minimise harmful bacteria and foodborne illness. The expected benefits are better tasting, safer and more nutritious foods.
Although public health policy currently dictates one generalised set of dietary guidelines for all of the population, one size does not necessarily fit all. There are many examples of how individuals respond differently to diet. For example, vitamin and mineral needs vary between individuals and by age, condition, health, etc. The effects of consuming phytochemicals, such as isoflavones and other flavonoids, or even starch, differs from person to person. Sodium increases blood pressure in some people but not others and the ability of dietary fibre to reduce cholesterol is also subject to genetic influences.
The time is approaching when it will be possible to use genetic testing to screen for the risk of various diseases and to determine an individual’s ideal health promoting diet. It will become commonplace for health care professionals to deliver tailor made drug advice based on an individual’s genetic information. Similarly, it will be possible to deliver dietary advice more precisely. Better knowledge on the functions of genes and their variation does not mean that we have to measure someone’s genes to allow them to take advantage of this knowledge. After all you don’t need a genetic test to know what sex you are! By the same token, a person won’t need to know their genetic variations in order for them to select diets that improve their health. Simple blood tests that provide now for such things as cholesterol will provide much of the assessment necessary to deliver more precise dietary advice.
Another potential use of research into the functions of genes is to improve food processing of the raw materials of foods, plants, animals and micro organisms. These raw commodities can be selected for optimal levels of various nutrients or to make processing easier, or more economical, or safer or even more nutritious. In fact, commodities will be selected to have better nutrients and better processing and safer and better flavour and more value. As a simple example, potatoes with higher levels of starch could be developed that when processed into potato chips or french fries,
would absorb less fat offering the choice of a low fat potato chip. Fruits and vegetables that have delayed ripening properties could be grown so that they can be transported more easily with less damage and arrive in stores fresher and tastier.
Many genes contribute either directly or indirectly to the flavour of a plant. Scientists can identify and study the genes responsible for flavour and aroma and use the information to improve the taste of foods.