Cosuppression of Genes (Gen Kosupresi)

Kosupresi adalah keadaan dimana ada banyak gen tanaman endogen, terjadi ekspresi yang berlebihan (over ekspresi) dari sense RNA atau mRNA dan menyebabkan pengurangan drastis dalam level ekspresi gen yang berkaitan.

Salah satu cara untuk memperoleh sebuah over ekspresi dari mRNA adalah dengan memasukkan sebuah konstruksi sense homolog dari gen yang berkaitan, sehingga akan menghasilkan sense RNA atau mRNA.

Efisiensi dari kosupresi bervariasi di antara gen tanaman. Kosupresi belum pernah teramati pada gen petunia chalcone isomerase, sedangkan pada gen nucleus tobacco glutamine synthetase selalu muncul kosupresi. Gen CHS (pada Petunia) merepresentasikan keadaan intermediet.

Mekanisme kosupresi tidak dapat dimengerti. Berdasarkan pada model ambang, ketika transkrip RNA dari get1e berakumulasi dalam tingkat kritik (situasi ambang), mereka secara selektif terdegradasi oleh RNase. Akumulasi tingkat tinggi transkrip RNA dari sebuah gen kemungkinan akan menyebabkan produksi transkrip sense RNA yang menyimpang dari transgen.

Sebuah akumulasi dari transkrip RNA yang menyimpang ditujukan untuk mengaktivasi RNA-dependen RNA polymerase tanaman asal, yang mentranskripsi transkrip RNA untuk memproduksi antisense RNA. Transkrip antisense RNA akan berasosiasi dengan akumulasi transkrip RNA yang normal dan yang menyimpang dari transgen, demikian juga pada gen endogen.

Hal ini akan menghasilkan RNA dupleks yang menunjukkan target untuk RNase spesifik RNA untai-ganda seperti pada RNase H. Degradasi transkrip RNA dari sebuah gen menunjukkan bahwa, entah bagaimana keadaan ini akan menyebabkan hipermetilasi sekuen homolog DNA sampai pada sekuen RNA terdegradasi. Seringkali hal ini juga menyebabkan reduksi drastis dalam tingkatan ekspresi transgen dan gen homolog endogen, jika ada. Inilah yang kemudian disebut dengan gene silencing.

Etilen adalah fitohormon yang penting dan ikut serta (bersama-sama dengan zat yang lainnya), dalam pematangan buah, seperti pada pisang, tomat, alpukat, dll., absisi daun dan pengguguran daun. Hormon ini diproduksi dari biosintesis etilen yang terjadi menurut urutan sebagai berikut: jika produksi etilen menurun akan menyebabkan tertundanya pengguguran mahkota pada bunga anyelir dan lambatnya pematangan buah tomat. Penurunan drastis produksi etilen telah diteliti, menurut jalur berikut:

① ekspresi konstruksi antisense ACC sintase atau ACC oksidase,
② kosupresi dari enzim-enzim, dan
③ ekspresi enzim yang memetabolisme S-adenosil metionin (SAM), seperti SAM hidrolase dari bakteriofase T3 (pada tomat), atau ACC, misalnya ACC daminase (over-ekspresi dalam tomat). Varietas bunga anyelir dengan vase hidup yang lama memiliki gen ACC sintase-nya sendiri yang ter-kosupresi. Sebuah pendekatan kosupresi yang sama telah digunakan untuk menghalangi serangan pematangan buah pada tomat.

Sumber:
1. http://www.molecular-plant-biotechnology.info/transgenic-plants-II/co-suppression-of-genes.htm
2. http://www.scq.ubc.ca/antisense-rna/

Ethical Dilemmas

Suppose that one day you are in the chemistry lab conducting an exercise by following the instructions given to you by your teacher. You have followed the instructions very closely and so far you have to completed all the steps and recorded all of your actions in your notebook. Suddenly you realize that the class will be over in five minutes and you still have the last step to finish. Since you know what will be the eventual outcome and time is running out, you are tempted to write up the last step as though you had completed the entire exercise. You feel that you have gained all the knowledge and experience that you can even without finishing the exercise. On the other hand, you realize that you are writing false data in your notebook and that you are not being truthful. What should you do?

One day you discover that your friend has taken money froma fund-raising activity in order to pay her lunch. You know that she is very poor and may not have enough money to pay for her lunch. You do not want to see her go hungry. Besides, the fund raising has gone extremely well and has made more than enough money to pay for the trip next month. Yet you know that stealing is wrong and that the theft should be reported. Should you report the theft or just look the other way?

These two series scenarios are what are known as ethical dilemmas. What is the correct thing to do in each instance? Logical-sounding arguments can probably be made for taking either action, and both deals with making a decision and taking an appropriate course of action based on what is right or wrong, moral or immoral. Almost every day we are faced with making decisions about what is the right thing to do. The solution may be simple and can be made without a lot of thought, or it may be extremely complicated to arrive at the right conclution. A concrete definition of ethics can fluctuate among individuals because of differing views on what is good, bad, moral, or immoral. Conflict often arises because of the differing values among people or even whole societies. A lot of the time, conflict comes about because people don’t understand the beliefs and values of those taking the opposite view the issue.

People with different religion backgrounds often have conflicting views. For example, the Hindu religion holds that cattle are sacred animals and are not to be used for beef. But other religions do not share this same conviction, finding it acceptable to use cattle for food and other purposes. Those of the Muslim and Jewish faith believe it is wrong to eat pork and meat from animals they deem unfit.

Ethics is also regulated by the facts of a particular situation. For instance, many people are against cosmetic companies using animals for product testing; however, when the situation is changed and animals are used for research to find cures for diseases, the general consensus shifts to support for animal research. The difference in opinion relates the perception of the risks and benefits on the research.

A huge task in solving an ethical problem is separating human emotions from factual information. An individual’s morals, values, and religious beliefs are often very strong ans are instrumental in developing the way people think. It is essential when analyzing a question of ethics to gather as much information on both sides of an issue as possible in order to make a responsible decision. Always keep in mind that ethics can vary from person to person depending on an individual’s perspective and background. The following sections will discuss some of the ethical issues faced by research scientists who develop biotechnology and by general public who are asked to accept and use the new discoveries.

Ethics in Cloning

Many consider cloning to be the most controversial area of biotechnology, with human cloning being more specific area of concern. Human cloning has been the subject of science fiction for decades, but it has only been in recent years that this technology has become a real likelihood. Cloning came to the forefront of the news in 1996 with the presentation of the cloned sheep Dolly. This milestone in scientific research was met with tremendous curiosity as well as a backlash of concern. The apprehensions ranged from religious concerns to questions of animal welfare. However, scientists involved in this field of research argue that species outweighs the associated risks. The potential benefits for cloning livestock are numerous and fascinating. A producer with a prize cow that can no longer reproduce can take advantage of cloning to ensure her genes influence the herd for years to come. Some people have even dreamed of using cloning in the horse industry. Imagine being able to clone a gelding that has exhibited tremendous talents in reining, cutting, or any other area of performance. Cloning him could produce a stallion that might pass on those desirable traits to offspring. What if producers could guarantee that each animal they sent to slaughter would grade choice or prime?

The possibilities of cloning are immense; but at the same time little is known about this developing area of science, and there may be valid concerns. For example, critics point out that although we have had success with cloning many animals, we still know relatively little about the long-term characteristics of cloned animals grow, develop, and age until we have a population of many hundreds of cloned animals to study. Critics question the ethics of producing this many animals through a process that we know so little about. Proponents argue that this is the case with any animal bred, since a purpose is an “unknown” until several generations have passed. They further contend that the animals that have been cloned appear to be, for the most part, as normal as any other animal.

From: Introduction to Biotechnology, Ray V Herren. page 349-350