Helicase – which unwinds the DNA double helix into two individual strands.Because each resulting DNA double helix retains one strand of the original DNA, DNA replication is said to be semi-conservative The incoming DNA double helix is split into two single strands and each original single strand becomes half of a new DNA double helix. In this process, many different proteins which are clustered together in particular locations in the cell act concertedly. In DNA Replication an entire double-stranded DNA is copied to produce a second, identical DNA double helix. One major difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA being replaced by the alternative pentose sugar ribose in RNA The asymmetric ends of DNA strands are called the 5′ and 3′ ends, with the 5' end having a terminal phosphate group and the 3' end a terminal hydroxyl group. In a double helix the strands are antiparallel. These asymmetric bonds mean each strand of DNA has a direction. The pentoses are joined together by phosphate groups that form phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar rings. The backbone of the DNA strand is made from alternating phosphate and 2-deoxy-ribose, a pentose. The DNA chain is 22 to 26 Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Å (0.33 nm) long. DNA is a long polymer made from repeating units called nucleotides.
