AP BIOLOGY

Detailed explanation-1: -DNA is always synthesized in the 5’-to-3’ direction, meaning that nucleotides are added only to the 3’ end of the growing strand. As shown in Figure 2, the 5’-phosphate group of the new nucleotide binds to the 3’-OH group of the last nucleotide of the growing strand.

Detailed explanation-2: -The need for accuracy probably explains why DNA replication occurs only in the 5′-to-3′ direction. If there were a DNA polymerase that added deoxyribonucleoside triphosphates in the 3′-to-5′ direction, the growing 5′-chain end, rather than the incoming mononucleotide, would carry the activating triphosphate.

Detailed explanation-3: -Each end of DNA molecule has a number. One end is referred to as 5’ (five prime) and the other end is referred to as 3’ (three prime). The 5’ and 3’ designations refer to the number of carbon atom in a deoxyribose sugar molecule to which a phosphate group bonds.

Detailed explanation-4: -DNA is made differently on the two strands at a replication fork. One new strand, the leading strand, runs 5’ to 3’ towards the fork and is made continuously. The other, the lagging strand, runs 5’ to 3’ away from the fork and is made in small pieces called Okazaki fragments.