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Biotechnology Principles and Processes Test - 22

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Biotechnology Principles and Processes Test - 22
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  • Question 1
    1 / -0
    A piece of nucleic acid used to find out a gene, by forming hybrid with it, is called as
    Solution
    cDNA (complementary DNA) is double-stranded DNA synthesised from an mRNA template. This conversion is carried out by the enzyme reverse transcriptase. This technique is often used to clone eukaryotic genes in the prokaryotes. The cloned eukaryotic cDNAs lack introns and other non-coding sequences present in the corresponding genome. 
    A DNA probe is a radioactively labelled DNA segment of variable length used to detect the presence of target nucleotide sequences in the DNA sample. The DNA probe is complementary to the target nucleotide sequences and thus, forms a hybrid with the sequence.
    Sticky ends refers to any two complementary ends of a molecule that can anneal. In case of DNA, the ssDNA ends with complementary base sequence to facilitate their base pairing to form a circular DNA. 
    Most of the restriction enzymes that introduce staggered cut in DNA at their restriction site create sticky ends. The blunt ends are the base paired ends of DNA. 
    Thus, the correct answer is option B. 
  • Question 2
    1 / -0
    Which of the following is the example of chemical scissors?
    Solution
    Restriction endonucleases are the enzymes that recognise specific sequences in the DNA and cut the DNA into fragments. The specific sites are 4-6 bp long and are called as restriction sites. Since these enzymes cut the DNA molecules into small fragments, they are also known as chemical/molecular scissors. They differ from regular scissors as they do not cut the DNA at random sites rather they recognise the specific DNA sequences for which they have complementary "teeth" just like a jigsaw puzzle pieces. EcoRI is restriction endonuclease enzyme present in E. coli as a part of the restriction modification system. The nucleic acid sequence of its restriction site is 5' GAATTC 3'. HindIII is type I restriction enzyme isolated from Haemophilus influenzae. It cuts the DNA at (5') AAGCTT (3'). BamHI  is a type II restriction endonuclease isolated from Bacillus amyloliquefaciens. It recognizes short sequences of DNA (5' GGATCC 3') and specifically cleaves DNA at this site. Since, all these enzymes have specific restriction sites, they are chemical scissors. 
    So, the correct answer is option D.
  • Question 3
    1 / -0
    How many copies of DNA sample are produced in PCR technique after 6-cycles?
    Solution
    • PCR technique amplify the gene of interest 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).
    • After completion of one cycle of PCR, two copies of the target DNA are produced both of which serve as a template for the next PCR cycle and produce 4 copies. 
    • Hence, there is an exponential amplification of DNA copies. 
    • The total number of DNA molecules, produced after "n" PCR cycle = 2n2^n. Thus, the total number of DNA molecules, produced after "6" PCR cycles = 262^6 = 64. 

    Thus, the correct answer is option C.
  • Question 4
    1 / -0
    Thermal cycle takes place in which of the following technique?
    Solution
    Gel electrophoresis is the technique used for separation of different nucleic acid molecules on the basis of their size. The gel is composed of polyacrylamide (for smaller DNA fragments) or agarose. An electric field is applied to gel that makes the negatively charged molecules through a matrix of gel. The molecules move according to their size. 
    PCR - technique amplify the gene of interest in three steps namely denaturation of target DNA (thermal cycle to separate the DNA strands), annealing of primers to the ssDNA and polymerization. 
    Centrifugation is the technique used for separation of components of a mixture based on their density and mass. It is carried out by subjecting particles in suspension to centrifugal forces. 
    Southern blotting is used for transfer of DNA from agarose gels to the membrane to analyze their composition. For the purpose, the agarose gel is mounted on the filter-paper wick and the hybridization membrane is sandwiched between the gel and an absorbent material, which draw the transfer buffer through the gel by capillary action. The buffer flow draws the DNA molecules which are then immobilized on the membrane. The correct answer is B.
  • Question 5
    1 / -0
    Chimeric DNA is a
    Solution
    Chimeric DNA is the recombinant DNA molecule or hybrid DNA that carries DNA segments from other sources, i.e., it is the mix of DNA from two different organisms. Uracil is a pyrimidine base which is present in RNA, not in DNA.
    DNA strands synthesized using RNA as template are called as complementary DNA (cDNA). This process is carried out by reverse transcription enzyme which copies RNA into DNA; it does not insert foreign DNA.
    DNA is a double stranded molecule but is also present as single stranded in some organisms; the single stranded DNA is not a hybrid DNA. 
    Recombinant DNA is the general name for a piece of DNA that has been created by the combination of at least two strands. Recombinant DNA molecules are sometimes called chimeric DNA, because they can be made of material from two different species, like the mythical chimera.
    So, the correct answer is 'Recombinant DNA'
  • Question 6
    1 / -0
    Function of restriction endonuclease enzyme is
    Solution
    Restriction systems identify the origin of incoming DNA and destroy it 
    if recognized as foreign. Restriction endonucleases recognize specific 
    sequences in the incoming DNA and digest the DNA into fragments. They 
    cut the DNA either at specific sites or more randomly. Hence, 
    restriction endonucleases are synthesized by bacteria as part of their defense mechanism. These enzymes are used in genetic engineering to cut the gene of the interest from source DNA and to introduce them into the vectors; but this is not a natural function of restriction endonucleases. Transcription is the process of synthesis of RNA using the DNA template. RNA polymerase perform this function by adding ribonucleotides to the RNA primer. Translation of nucleotide sequence of mRNA into amino acid sequence of protein is called as protein synthesis. It is performed by tRNA. Restriction enzymes do not play any role in these two processes. Correct option is B.
  • Question 7
    1 / -0
    A bacterium modifies its DNA by adding methyl groups to the DNA, It does so to
    Solution
    • Restriction endonucleases recognize specific sequences in the incoming DNA and digest the DNA into fragments. 
    • They cut the DNA either at specific sites and are synthesized by bacteria as part of their defense mechanism. 
    • The restriction sites are very short sequences and can be present in their own DNA. 
    • Its own DNA is protected from destruction by adding methyl groups to it. 
    • Only a few specific bases are modified on each strand.

    Thus, the correct answer is option D.
  • Question 8
    1 / -0
    When the number of genes increases in response to some signal the effect is called as
    Solution
    Gene pool is the sum total of all genes present in a reproductive gametes of a population which are then transferred from parent to offspring. Gene frequency refers to proportion of different genes in a population; gene frequency of offspring is determined by that of parents. The number of copies of a gene present in a cell or nucleus of an individual is known as gene dosage. An increased gene dosage leads to higher levels of gene product provided the gene is not under regulation from elsewhere in the body. Gene amplification is increasing the number of copies of a gene, i.e., increase in gene dosage. It takes place when a multigene family carries mutant gene/genes. Correct answer is C.
  • Question 9
    1 / -0
    Which of the following enzyme is used to join DNA fragments?
    Solution
    DNA ligase joins the annealed cohesive ends produced by certain restriction enzymes and also catalyze the formation of phosphodiester bonds between blunt-ended fragments of DNA to join them together. DNA polymerase catalyzes the polymerization of nucleotides to form DNA and requires both a primer (a short oligonucleotide strand), to which nucleotides are added, and a template strand to guide selection of each new nucleotide. Endonucleases are the enzymes that breaks phosphodiester bond within a polynucleotide chain. For example, restriction endonucleases recognize and cleave DNA at specific DNA sequences (recognition sequences or restriction sites) to generate a set of smaller fragments. Terminase enzymes are involved in cutting and packaging the viral genome.
    So, the correct answer is 'Ligase'
  • Question 10
    1 / -0
    The restriction enzyem EcoRI has the property of 
    Solution
    Restriction endonucleases recognise specific sequences in the DNA and cut it into small fragments. The specific sites are 4-6 bp long and are called as restriction sites. Each restriction endonuclease has a specific restriction site. Ligase enzyme joins two large molecules by forming a new chemical bond; for example, DNA ligase joins two DNA fragments together via phosphodiester bond between two nucleotides. 
    Exonucleases enzymes remove nucleotides one at a time from the end of a polynucleotide chain. They shorten the DNA by one nucleotide at a time, they do not digest it into fragments. 
    DNA denaturation by helicases creates topological stress in the helical DNA structure which is relieved by the action of topoisomerases. These enzymes transiently break both DNA strands of one chromosome thereby making the other chromosome to pass through the break and relieve the stress. 
    EcoRI is present in E. coli as a part of the restriction modification system. The nucleic acid sequence of its restriction site is 5' GAATTC 3'. It cuts the DNA between G and A in the above-mentioned sequence. Since EcoRI does not cut the DNA randomly but has specific restriction site and cut DNA within the nucleotide chain; it is a restriction endonuclease. 
    So, the correct answer is option A.
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