PROCESS OF GENETIC ENGINEERING

Genetic engineering is the process of manually adding new DNA to an organism. The goal is to add one or more new traits that are not already found in that organism. Examples of genetically engineered (transgenic) organisms currently on the market

Review Questions :

Identify the word being described by the given statement. ______________1. part of the flower that produces the pollen

______________2. animals having both the male and female sex organs ______________3. a type of reproduction which uses only the cells from one parent

______________4. flowers having both the reproductive organs ______________5. the fertilized egg of animals

include plants with resistance to some insects, plants that can tolerate herbicides, and crops with modified oil content.

DNA

Deoxyribonucleic acid or DNA is a genetic material which is stored in the nucleus. The nucleus is a part of the eukaryotic cell and contains nucleic acids and it is responsible in protein production. Small segments of DNA are called genes. Each gene holds the instructions for how to produce a single protein.

DNA is usually a double-helix and has two strands running in opposite directions.

DNA is the recipe for life. It is a molecule found in the nucleus of every cell and is made up of 4 subunits called bases and are represented by the letters A ( Adenine ), T ( Thymine), G ( Guanine ), and C ( Cytosine ). The order of these subunits in the DNA strand holds a code of information for the cell. The genetic language uses 4 letters to spell out the instructions for how to make the proteins an organism will need to grow and live. Structures of the Bases

Pairing of Subunits

In the double-stranded DNA, the two strands run in opposite directions and the bases pair up such that A always pairs with T and G always pairs with C. The A-T base- pair has 2 hydrogen bonds and the G-C base-pair has 3 hydrogen bonds. The G-C interaction is therefore stronger (by about

30%) than A-T, and A-T rich regions of DNA are more prone to thermal fluctuations.

The smaller base is always paired with a bigger one. The effect of this is to keep the two chains at a fixed distance

from each other all the way along. These particular pairs fit exactly to form very effective hydrogen bonds with each other. It is these hydrogen bonds which hold the two chains together.

Exploring a DNA chain

The backbone of DNA is based on a repeated pattern of a sugar group and a phosphate group. The full name of DNA, deoxyribonucleic acid, gives the name of the sugar present - deoxyribose.

Deoxyribose is a modified form of another sugar called ribose. Ribose is the sugar in the backbone of RNA, ribonucleic acid.

Each of the four corners where there isn't an atom shown has a carbon atom in the ring.

Deoxyribose, as the name might suggest, is ribose which has lost an oxygen atom - "de-oxy".

Numbering of carbon atoms in deoxyribose ring The carbon atom to the right of the oxygen is numbered 1, and then around (clockwise direction ) to the carbon on the CH2OH side group as number 5.

Attaching a phosphate group

The other repeating part of the DNA

backbone is a phosphate group. A phos- phate group is attached to the sugar molecule in place of the –OH group

on the 5’ carbon

Attaching a base and making a nucleotide

One of four bases, cytosine (C) , thymine ( T ), adenine ( A ), and guanine ( G ), is added to the above structure to form a DNA strand ( nucleotide ).These bases attach in place of the -OH group on the 1' carbon atom in the sugar ring.

simplified

nucleotide

diagram of

nucleotide

Location of Bonding on Base Structures with Sugar Ring

These bases attach in place of the –OH group on the 1’ carbon atom in the sugar ring. The nitrogen and hydrogen atoms ( in blue ) on each molecule show where these molecules join on to the deoxyribose. In each case, the hydrogen is lost together with the -OH group on the 1'

OH O – P = O

carbon atom of the sugar. This is a condensation reaction - two molecules joining together with the loss of a small one (not necessarily water).

Example of nucleotide containing cytosine

Joining the nucleotides into a DNA Strand

A DNA strand is simply a string of nucleotides joined together. The phosphate group on one nucleotide links to the 3’ carbon atom on the sugar of another one. In the process, a molecule of water is lost – another condensation reaction.

Adding more nucleotides in the same way build up a DNA chain for one strand. Pairing the two strands of DNA chains forms the structure resembling a ladder twisted into a spiral , called the double helix. One chain of DNA strand

Final structure for DNA with 2 strands , each at opposite direction

How is genetic engineering done?

Genetic engineering, also called transformation, works by physically removing a gene from one organism and inserting it into another, giving it the ability to express the trait encoded by that gene.

The process of genetic engineering requires the successful completion of five steps :

Step 1 : DNA Extraction

DNA is extracted from the desired organism. A sample of an organism containing the gene of interest is taken through a series of steps to remove the DNA.

Step 2 : Gene Cloning

The second step of the genetic engineering process is gene cloning. During DNA extraction, all of the DNA from the organism is extracted at once. Scientists use gene cloning to separate the single gene of interest from the rest of the genes extracted and make thousands of copies of it.

Step 3 : Gene Design

Once a gene has been cloned, genetic engineers begin the third step, designing the gene to work once inside a different organism. This is done in a test tube by cutting the gene apart with enzymes and replacing gene regions that have been separated.

Step 4 : Transformation or Gene Insertion

Since plants have millions of cells, it would be impossible to insert a copy of the transgene into every cell. Therefore, tissue culture is used to propagate masses of undifferentiated plant cells called callus. These are the cells to which the new transgene will be added.

The new gene is inserted into some of the cells using various techniques. Some of the more common methods include the gene gun, agrobacterium, micro-fibers, and electroporation. The main goal of each of these methods is to transport the new gene(s) and deliver them into the nucleus of a cell without killing it. Transformed plant cells are then regenerated into transgenic plants. The transgenic plants are

grown to maturity in greenhouses and the seed they produce, which has inherited the transgene, is collected.

Step 5 : Backcross Breeding

Transgenic plants are crossed with elite breeding lines using traditional plant breeding methods to combine the desired traits of elite parents and the transgene into a single line. The offspring are repeatedly crossed back to the elite line to obtain a high yielding transgenic line. The result will be a plant with a yield

potential close to current hybrids that expresses the trait encoded by the new transgene

.

Genetic engineering compared to traditional breeding

Although the goal of both genetic engineering and traditional plant breeding is to improve an organism’s traits, there are some key differences between them.

While genetic engineering manually moves genes from one organism to another, traditional breeding moves genes through mating, or crossing, the organisms in hopes of obtaining offspring with the desired combination of traits.

Traditional breeding is effective in improving traits, however, when compared with genetic engineering, it does have disadvantages. Since breeding relies on the ability to mate two organisms to move genes, trait improvement is basically limited to those traits that already exist within that species. Genetic engineering, on the other hand, physically removes the genes from one organism and places them into the other. This eliminates the need for mating and allows the movement of genes between organisms of any species. Therefore, the potential traits that can be used are virtually unlimited.

Breeding is also less precise than genetic engineering. In breeding, half of the genes from each parent are passed on to the offspring. This may include many undesi- rable genes for traits that are not wanted in the new organism. Genetic engineering, however, allows for the movement of a single, or a few, genes.

The improvement of crops with the use of genetics has been occurring for years. Traditionally, crop improvement was accomplished by selecting the best looking plants/seeds and saving them to plant for the next year’s crop.

Plant breeding is an important tool, but has limitations. First, breeding can only be done between two plants that can sexually mate with each other. This limits the new traits that can be added to those that already exist in that species. Second, when plants are mated, (crossed), many traits are transferred along with the trait of interest including traits with undesirable effects on yield potential.

Genetic engineering is a new type of genetic modification. It is the purposeful addition of a foreign gene or genes to the genome of an organism. A gene holds information that will give the organism a trait. Genetic engineering is not bound by the limitations of traditional plant breeding. Genetic engineering physically removes the DNA from one organism and transfers the gene(s) for one or a few traits into another. Since crossing is not necessary, the 'sexual' barrier between species is overcome. There- fore, traits from any living organism can be transferred into a plant. This method is also more specific in that a single trait can be added to a plant.

Lesson 6.3: BENEFITS AND RISKS OF USING GMOs