AP BIOLOGY

Detailed explanation-1: -Primers are required because DNA polymerases, the enzymes responsible for the actual addition of nucleotides to the new DNA strand, can only add deoxyribonucleotides to the 3’-OH group of an existing chain and cannot begin synthesis de novo.

Detailed explanation-2: -They always need a template. They can only add nucleotides to the 3’ end of a DNA strand. They can’t start making a DNA chain from scratch, but require a pre-existing chain or short stretch of nucleotides called a primer.

Detailed explanation-3: -Since DNA polymerase requires a free 3’ OH group for initiation of synthesis, it can synthesize in only one direction by extending the 3’ end of the preexisting nucleotide chain. Hence, DNA polymerase moves along the template strand in a 3’–5’ direction, and the daughter strand is formed in a 5’–3’ direction.

Detailed explanation-4: -The nucleotide exists in the triphosphate form before being added to the chain, and the removal of two of the phosphate groups provides the energy to bind it to the growing chain. This is why nucleotides are only added on the 3’ end.

Detailed explanation-5: -DNA Synthesis In Vivo and In Vitro DNA polymerase cannot initiate new strands of nucleic acid synthesis because it can only add a nucleotide onto a pre-existing 3′-OH. Therefore, an 11 to 12 base-pair length of RNA (an RNA primer) is made at the beginning of each new strand of DNA.