Question

After 4 PCR cycles, how many DNA molecules are formed from one DNA template molecule?
A. 4
B. 32
C. 16
D. 8

Answer 1

Hint: PCR or Polymerase Chain Reaction, is a process of amplification of a given template of DNA, by utilizing various primers supplemented with free nucleotides and a polymerase enzyme. PCR finds an important application in genetic engineering and even in investigational forensics. The PCR process can amplify a single DNA to $2^n$ times, where n is the number of cycles. Thus for 4 cycles of PCR, a given DNA template can be amplified to 16 duplicate strands.

Complete answer:PCR, also known as Polymerase Chain Reaction, as the name suggests is a chain of reactions that are initiated by predefined DNA strands called primers, which make multiple copies of a given single strand of DNA with the help of a polymerase enzyme.
Invented in 1942, by Karry Mullis, PCR had found its primary use in genetic engineering, where a single strand of DNA is amplified for further analysis and studies. This is also one of the base components of DNA Fingerprinting in forensic sciences where a small DNA sample obtained from a crime scene can be amplified and studied.
The primary mechanism behind PCR is thermal cycling. This is a process where there is an interval of heating and cooling which initiates various reactions such as DNA replication, DNA cleaving, and much more.
A single cycle of the PCR setup can be divided into denaturation, annealing and elongation. The denaturation phase is where the double-stranded DNA is split into two. In the annealing phase, the temperature is lowered so that primers can attach to the single DNA strands, and in the elongation phases, the polymerase enzyme replicates the DNA strands. Now the DNA strands fuse to become double-stranded DNA at the end of final elongation.
So, for one cycle, a single DNA template splits into 2 single strands, both of which get replicated. So, in the middle of the cycle, we have 4 single-stranded DNA, 2 sense and 2 antisense, and when they cool at the end of the cycle, they fuse to form 2 similar DNA strands.
For the next cycle, the 2 strands from the first cycle act as templates and will yield 4 strands at the end of the second cycle and so on. Thus, the formula $2^n$ is employed to identify the number of duplicates formed based on the cycle.

Thus, the correct answer is option C, 16, as $2^4=16$

Note:
PCR is a process of amplification of template DNA
Important chemicals used are Taq polymerase, primers, free nucleotides.
Thermal cycling ensures the initiation and termination of each phase
Each phase of a single cycle has specific temperature requirements depending on the type of DNA being amplified.