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i. The recognition sequence shows palindrome character in which the sequence of base pairs read the same on both the DNA strands, i.e., same in 5′ → 3′ or 3′ → 5′ directions, e.g.,

5′ — G A A T T C — 3′

3′ — C T T A A G — 5′

ii. The restriction endonuclease acts on specified length of a DNA and binds to the DNA at the recognition sequence.

iii. It cuts the opposite double helix of DNA in the sugar-phosphate backbones, at little away from the centre of the palindrome sites.

iv. There are overhanging stretches called sticky ends on each strand, which form hydrogen bonds with their complementary cut counterparts. This stickiness of the ends facilitates the action of the enzyme DNA ligase.

Agrobacterium tumifaciens is a soil bacterium which causes disease in many dicot plants. It is able to deliver a piece of DNA known as T-DNA, to transform the normal cells into tumour cells and direct these tumour cells to produce the chemicals required by the pathogen. The tumour inducing (Ti) plasmid of Agrobacterium tumifaciens has now been modified into a cloning vector which is no more pathogenic to the plants but still deliver genes of interest into a variety of plants.

a) plasmid  

b) The bacteria delivers a piece of DNA know as T-DNA in the genome of host plant cell to transform it into a tumour cell. 

c) Cloning vector

• Low concentration of viral or bacterial DNA in the host cell/body can be detected much before the symptoms of the disease appear i.e. early detection of disease is possible 
• Clones of genes can be used to as probe to detect the presence of mutual alleles in cancer suspected patients.

Enzymes that cut the phosphodiester bonds of polynucleotide chains are called as nucleases.

No, our blood does not contain enzymes proteases and nucleases. If these two enzymes were there in the blood, it causes the degeneration of blood cells and lining cells of blood cells.

• Transgenic animals are designed to allow the study of how genes are regulated and how they affect the normal functions of the body and its development
• eq: Information is obtained as to how insulin has a role as growth factor
• They are designed to increase our understanding as to how genes could control the development of disease, they serve as models of human disease.
• They produce useful biological compounds created by introducing a portion of the DNA that code for the products.
• eg: a-1 antitrypsin is produced for treating emphysema
• They are being developed to test the safety vaccines,
• eg: Polio vaccines has been tested on mice 
• Transgenic animals with more sensitivity to toxic substance are being developed to the test the toxicity of drugs.

Concerns about transgenic insulin

• The removal of C-peptide during maturation 
• Assembling of the a and p polypeptides together to form mature form of insulin.

They are organisms which have been modified genetically through introduction of genes of another organism artificially by the technique of genetic engineering instead of conventional hybridisation.

• a-1- antitrypsin is used to treat emphysema.
• a – lactalbumin is produced in the milk of the transgenic cow, Rosie, this is nutritionally more balanced product for human babies than normal cow milk.

T-DNA is the only essential part required to make Ti plasmid a cloning vector. The plasmid is disarmed by deleting the tumour inducing genes in the plasmid so that it becomes an effective cloning vector and remove it harmful effect.

1. The two types of nucleases are exonucleases and endonucleases. 

2. Exonucleases remove nucleotides from the ends of the DNA. 

3. Endonucleases are those enzymes that have ability to make cuts at specific positions within the DNA molecule. 

4. Of the endonucleases, restriction endonucleases serve as the molecular scissors in genetic engineering experiments. 

5. They are used for cutting DNA molecules at specific predetermined sites. This is needed for gene cloning or recombinant DNA technology.

Transgenic bacteria are microbes carrying clones of foreign genes. It is also known as genetically modified bacteria. These bacteria are being employed for many functions .

(a) Two DNA sequence (coding for A and B chains of human insulin) were introduced into the plasmid of bacteria E. Coli. This transgenic bacteria produced insulin chain- Used as biochemical factories

(b) Microbes have been genetically changed to help in cleaning the polluted environment, 

eg:- Pseudomonas putida for cleaning oil spills pseudomonas species for removing heavy metal pollutants. Aceto bacter aerogans for decomposition of DDT and Flavobacterium for decomposition of 2,4-D.

Downstream processing

• All the processes to which a product is subjected to before being marketed as a finished product are called downstream processing.

• It includes:

a. Separation of the product from the reactor.

b. Purification of the product.

c. Formulation of the product with suitable preservatives.

d. Quality control testing and clinical trials in case of drugs.

It is the therapeutic treatment of defective heredity by the introduction healthy and functional gene which also silence the defective genes of an individual.

OR

The replacement of a nonfunctional or defective gene with a normal functional gene is called gene therapy. A person with defect in the gene for the enzyme adenosine deaminase (ADA) suffers with SC1D (Severe Combined Immuno Deficiency) The enzyme ADA is crucial for the immune system. Ideally gene therapy should be applied to the zygotes so that the progeny of defective individual also gets rid of effect. It is however, generally applied to somatic cells where the defect occurs. 

At first step towards gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. A functional ADA cDNA (using a retrovirus vector) is then introduced into these lymphocytes which are subsequently returned to the patient. Since these cells are not immortal, the patient requires periodic infusion of such genetically engineered lymphocytes.

Different types of restrictions enzymes are as follows:

1. Type I – They function . simultaneously as endonuclease and methylase e.g. EcoK. 

2. Type II – They exhibit separate cleaving and methylation activities. They are more stable and are used in r-DNA technology e.g. EcoRI, Bgll. They cut DNA at specific sites within the pallindrome. Thousands of type II restriction enzymes have been discovered. 

3. Type III – They cut DNA at specific nonpalindromic sequences e.g. Hpal, MboII.

1. Agrobacterium tumefaciens is a soil bacterium that causes crown gall disease in plants. 

2. This disease involves the formation of tumor in the plant. 

3. Ti plasmid in A. tumefaciens contains a transposon called T DNA.

4. T DNA inserts copies of itself into the chromosomes of infected plant cells. 

5. The transposons, with the foreign DNA, can be inserted into the host cell’s chromosomes. 

6. A plant cell containing this DNA, can then be grown in culture or induced to form a new, transgenic plant.

construction of Genomic library:

1. When genomic library is constructed, the entire genome or DNA is isolated from a particular organism. 

2. This DNA is fragmented using suitable restriction endonucleases. 

3. These separated fragments are later inserted into cloning vectors. 

4. This develops recombinant vectors. 

5. Such recombinant vectors are transferred into suitable organisms such as bacteria or yeast. Each host cell then contains one fragment. 

6. These transformed organisms are cultured and their clones are thus produced. These clones are stored in the genomic library.

1. Palindrome is a sequence which when read on opposite strands of DNA (3′ to 5’ or 5’ to 3’), reads same. 

2. When the enzyme EcoRI recognizes this sequence, it breaks each between the A and G residues. 

3. In palindrome, the base sequence of second half in DNA represents the mirror image of the base sequence of the first half.

4. Palindromes are actually groups of letters which form the same word when read in both forward and backward directions.

For example, recognition sequence of by the enzyme 

EcoRI is a palindrome. 

3′ —— – C T T A A G—–5′ 

5′ —— – G A A T T C—–3′

Same restriction enzyme must be used to cut vector and donor DNA, because it will produce fragments with the same complementary sticky ends, making it bond formation possible between them.

Sticky ends are short extensions of cleaved DNA molecule which can form hydrogen bonded base pairs with other complementary sticky ends.

Restriction is the process by which the DNA strand is cut into restriction fragments with the help of restriction endonuclease enzymes or REs.

Palindrome is a DNA sequence which when read on opposite strands of DNA (3′ to 5′ or 5′ to 3′) it reads same.

Correct answer is (c) endonucleases