Final answer:
During PCR, nucleotide triphosphates (dNTPs) are added to the growing DNA strand during the extension/elongation phase. This involves adding complementary nucleotides to the DNA template strand.
Step-by-step explanation:
The nucleotide triphosphates (dNTPs) are added to the growing DNA strand during the extension/elongation phase of PCR (Polymerase Chain Reaction).
In this phase, an enzyme called DNA polymerase adds complementary nucleotides to the DNA template strand, which results in the elongation of the DNA molecule.
For example, if the template strand has the sequence 'AGTC,' the added nucleotides would be 'T,' 'C,' 'A,' and 'G,' respectively, creating the complementary strand 'TCAG.'