Which enzyme is responsible for synthesizing new DNA strands during PCR?
Answer: A
Taq DNA polymerase from Thermus aquaticus is heat-stable and essential for DNA synthesis in PCR cycles.
Q.2Easy
In PCR, the denaturation step typically occurs at:
Answer: B
Denaturation separates double-stranded DNA into single strands, requiring high temperatures of 94-95°C.
Q.3Easy
Restriction enzymes recognize and cut DNA at:
Answer: B
Restriction endonucleases recognize specific palindromic DNA sequences and cut predictably at these sites.
Q.4Easy
The role of DNA ligase in genetic engineering is to:
Answer: B
DNA ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides, joining DNA fragments.
Q.5Easy
The polymerase chain reaction was invented by:
Answer: B
Kary Mullis invented PCR in 1983, a revolutionary technique that earned him the Nobel Prize in Chemistry in 1993.
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Q.6Easy
The extension step in PCR occurs at approximately:
Answer: B
Extension/elongation happens at 72-75°C, the optimal temperature for Taq polymerase to synthesize DNA.
Q.7Easy
In PCR, which enzyme synthesizes the complementary DNA strand during the extension phase?
Answer: A
Taq polymerase (thermostable DNA polymerase from Thermus aquaticus) synthesizes new DNA strands at 72°C during the extension phase of PCR.
Q.8Easy
What is the typical number of PCR cycles required to achieve exponential amplification of target DNA?
Answer: B
Standard PCR typically uses 25-35 cycles to achieve sufficient exponential amplification (2^n copies) without compromising specificity or introducing errors.
Q.9Easy
Which of the following is NOT a component of the PCR reaction mixture?
Answer: D
Restriction enzymes are used in DNA cloning and digestion, not in PCR. PCR requires template DNA, primers, dNTPs, Taq polymerase, and buffer.
Q.10Easy
In DNA sequencing by Sanger method, what role do ddNTPs play?
Answer: B
ddNTPs (dideoxynucleotides) lack a 3'-OH group, causing chain termination when incorporated, generating DNA fragments of different lengths for sequencing.
Q.11Easy
During PCR amplification, which enzyme synthesizes new DNA strands by reading the template DNA in the 3' to 5' direction?
Answer: B
Taq DNA Polymerase (thermostable polymerase from Thermus aquaticus) is the standard enzyme used in PCR. It synthesizes DNA by adding nucleotides to the 3'-OH group of the growing strand.
Q.12Easy
What is the typical temperature range for the annealing step in a standard PCR cycle?
Answer: A
The annealing temperature typically ranges from 50-65°C and depends on the primer's melting temperature (Tm). This allows primers to bind specifically to complementary sequences on the template DNA.
Q.13Easy
In real-time PCR (qPCR), which fluorescent dye binds directly to double-stranded DNA and is most commonly used in 2024-25 diagnostics?
Answer: A
SYBR Green intercalates into double-stranded DNA and fluoresces. It is cost-effective and widely used in qPCR for gene expression studies and viral load detection.
Q.14Easy
What is the primary principle behind whole exome sequencing (WES) in identifying disease-causing mutations?
Answer: A
WES captures and sequences exonic regions (~50 Mb) using targeted enrichment, reducing sequencing depth and cost while identifying 85-90% of disease-causing variants.
Q.15Easy
What is the optimal annealing temperature range for most PCR reactions?
Answer: A
The annealing temperature typically ranges from 45-65°C and depends on the Tm (melting temperature) of the primers used. This temperature allows primers to bind specifically to target DNA.
Q.16Easy
Which thermostable DNA polymerase is most commonly used in standard PCR?
Answer: A
Taq polymerase, isolated from Thermus aquaticus, is the most widely used enzyme in PCR due to its heat stability and ability to synthesize DNA at high temperatures.
Q.17Easy
In a typical PCR cycle, DNA denaturation occurs at approximately which temperature?
Answer: B
DNA denaturation in PCR occurs at 94-95°C (or sometimes 98°C), where hydrogen bonds between DNA strands are broken, separating the double helix into single strands.
Q.18Easy
What is the primary function of dNTPs in PCR?
Answer: B
dNTPs (deoxynucleotide triphosphates) are the precursor molecules that DNA polymerase incorporates into the growing DNA strand during the extension phase of PCR.
Q.19Easy
Which enzyme is primarily responsible for extending DNA strands during the elongation phase of PCR?
Answer: A
Taq polymerase, derived from Thermus aquaticus, is a heat-stable DNA polymerase that extends primers during PCR elongation at 72°C.
Q.20Easy
In a standard PCR cycle, at what temperature is the DNA double helix typically denatured?
Answer: C
Denaturation occurs at 94-95°C where hydrogen bonds between complementary DNA strands break, separating double-stranded DNA into single strands.
