CBSE Questions for Class 12 Medical Biology Biotechnology: Principles And Processes Quiz 13 - MCQExams.com

• PCR stands for a polymerase chain reaction. This is a technique used to amplify a given sample of DNA. 
• In this the first step is to denature the DNA template by melting the hydrogen bonds and making it into a single strand at 94 degrees celsius.
• The second step involves the annealing step that involves joining the primers to the single-stranded DNA.
• Then this step is followed by the extension or elongation step that involves the extension of the DNA by the Taq polymerase by the addition of the nucleotides. 

• Autoradiography includes labelling of biomolecules with radioactive material (radioactive thymine for DNA, radioactive uracil for RNA, and radioactive S for proteins) followed by localizing these radioactively labelled molecules by applying photosensitive emulsion on the surface of prepared slides. 
• In gel electrophoresis, an electric field is applied to gel that makes the negatively charged DNA fragments move through a matrix of gel and thereby allows sorting of these fragments according to their size. 
• PCR is a technique that amplifies the DNA sample in three steps namely denaturation of target DNA (thermal cycle to separate the DNA strands), annealing of primers to the ssDNA, and polymerization (extension of primer into complete DNA strand complementary to the template strand). 

$$\textbf{Correct answer: B}$$ 

$$\textbf{Option (A):}$$ 

$$\bullet$$ Preservation is a part of downstream processing because after the products are purified the preservation process needs to be performed so that they can be stored for a longer period. 

$$\textbf{Option (B):}$$ 

$$\bullet$$ Expression is a component of the process of biosynthesis.

$$\bullet$$ This occurs in the bioreactor and not during downstream processing. 

$$\bullet$$ Expression is the ability to produce the product using the given substrate in the medium. 

$$\textbf{Option (C):}$$ 

$$\bullet$$ Separation is the process of separating the cellular debris and the remnants of the media from that of the end product.

$$\bullet$$ When the product is collected from the bioreactor, all these come out of the outlet pipes. 

$$\bullet$$ The separation process helps in the removal of unnecessary products. 

$$\textbf{Option (D):}$$ 

$$\bullet$$ To avoid contamination in the actual product the purification process needs to be performed. Different chemical molecules have different purification processes.

$$\bullet$$ Depending on the chemical nature of the molecule the purification process is performed to get the absolute end products without any contaminants.

Hence, the correct answer is option (B).

• PCR (Polymerase Chain Reaction) is the process of amplification of the DNA. The enzyme Taq polymerase is the enzyme that is used to add the nucleotides to the copies of new DNA which are synthesized. The enzyme is stable at various temperatures and does not gets denatured when the PCR is carried out at different temperatures in different stages. 
• Downstream processing involves the various steps which are carried out to separate the product and then purify. This step is performed when the product is obtained in the crude form. These are the steps that are important with respect to quality control. 
• Restriction endonuclease is the enzymes that are used for the cleavage of the DNA at specific sites. There is a recognition site at which there is a specific base sequence that allows cleavage at the proper site. EcoRI is the restriction enzyme that is isolated from E.coli. 
• Selectable markers are the specific genes that are used to identify the transformants and the non-transformants after the process of recombination. The ampicillin gene is commonly used as a selectable marker.

• Gel electrophoresis helps in the separation of DNA, RNA, or proteins according to their molecular size. 
• It forms a major part of applications of biotechnology like DNA fingerprinting where it is used to separate the loaded sample on the basis of their size.
• Ethidium bromide is the fluorescent material which is exposed to U.V light for fluorescence effect. 
• It DNA tagged by it can easily be traced out on the transparent gel.
• So, the correct answer is option A.

• The palindromic sequences are the sequences of the nucleotides which are the same when reading from either side. 
• These are the sequences that are present on the DNA or RNA double helix. 
• The sequence is the same when reading from 5' to 3' on one strand and 3' to 5' on the other. Option C not satisfying the same condition. 

• Avery, McCarty and MacLeod are the scientists who performed the experiments which proved that the transforming principle is the DNA.
• The DNA of the virulent bacteria helped in the conversion of the DNA of the non-virulent bacteria.
• The non-virulent bacteria were transformed into a virulent form. The DNAse is the enzyme that can destroy the DNA. 
• It causes cleavage of the nucleotides in the sequence of the DNA. 

$$\textbf{Correct answer: C}$$ 

$$\textbf{Option (A):}$$ 

$$\bullet$$ The two strands of DNA have the base sequence complementary to one another. 

$$\bullet$$ There is no mutation because all the nucleotide bases are perfectly complementary to one another. 

$$\bullet$$ There are no base mutations or changes in sequence observed in the two stems. 

$$\textbf{Option (B):}$$ 

$$\bullet$$ The start codon is present in the mRNA sequence.

$$\bullet$$ The AUG codon codes for methionine which starts the process of translation. This initiates the process of polypeptide chain formation.

$$\textbf{Option (C):}$$ 

$$\bullet$$ The given sequence is a palindromic sequence because the two DNA strands read the same from the 5' to 3' direction. 

$$\bullet$$ These are the sequences that act as the recognition site for the restriction enzyme where the DNA is cut into fragments. 

$$\textbf{Option (D):}$$ 

$$\bullet$$ This sequence does not show the completion of DNA replication.

Hence, the correct answer is option (C).

• PCR - technique amplifies the DNA sample in three steps namely denaturation of target DNA, annealing and polymerization. 
• Denaturation refers to the thermal cycle that separates the DNA strands and forms the ssDNA. 
• Annealing refers to the pairing of primers to the ssDNA and polymerization is the extension of primer into complete DNA strand complementary to the template strand. 

• The z-gene controls beta-galactosidase enzyme as it is inserted on the DNA sequence it becomes inactivated by the process of insertional activation and the normal blue colour of cell culture with active beta-galactosidase will not appear but due to its absence, it will be of white coloured and will be of recombinant nature. However the non-recombinants formed were of blue colour.