Q20.1-4CC. Compare Figure 20.7 with Figure ... [FREE SOLUTION]

Chapter 20: Q20.1-4CC. (page 421)

Compare Figure 20.7 with Figure 16.20. How does replication of DNA ends during PCR proceed without shortening the fragments each time?

Short Answer

Expert verified

The synthesis of a new strand contains RNA nucleotides in primer, which are not replaced by DNA polymerase in the DNA replication process. This leads to the synthesis of a daughter DNA molecule of a shorter length.

In contrast, PCR contains DNA nucleotides in primers that do not need to be replaced and become part of the new strand. As a result, copies produced are of the desired size.

Step by step solution

PCR (Polymerase chain reaction)

In PCR, the desired DNA sequence is copied. In this process, short stretches of DNA called primers are used that bind to either side of the DNA segment and initiate the PCR reaction process.

Thus, a double-stranded molecule of DNA of the desired size is produced at the end of the cycle.

DNA Replication

DNA replication is a process that doubles the DNA while retaining the genetic information encoded in the base sequence. This process requires a template strand for sequence information.

DNA replication uses RNA primer, which is extended based on the template strand sequence and results in the synthesis of the new strand. As a result, a new DNA molecule with a new strand and an old strand is synthesized.

Replicated DNA fragments have an exact length as that of the target sequence used

In DNA replication, the newly synthesized strand contains RNA nucleotides in RNA primer that needs to be removed and replaced by DNA nucleotides at the 3鈥� end. However, DNA nucleotides cannot be added to the new strand in place of RNA primers because the 3鈥� end is not available for DNA polymerase to add nucleotides.

As a result, the daughter molecules produced are shorter in length. The length of the daughter molecules reduces further with subsequent cycles.

However, the DNA nucleotides of the primers become part of the new strand in the PCR. As a result, the copies produced at the end of the cycle are of exact length as the desired DNA sequence.