When the two strands of DNA double helix are separated, each can serve as a template for the replication of a new complementary strand, producing two daughter molecules each of which contains two DNA strands with an antiparallel orientation. The enzymes involved in DNA replication process are template-directed polymerases that can synthesize the complementary sequence of each strand with extraordinary fidelity. This complex leads to the local denaturation and unwinding of an adjacent A + T rich region of DNA. The interaction of proteins with the origin is what defines the start site of replication and provides a short region of single stranded DNA essential to initiation of synthesis of the nascent DNA strand. Then helicase binds and allows for processive unwinding of double stranded DNA into single stranded DNA. As helicase unwinds the DNA, DNA single stranded protiens bind and stabilize the single stranded DNA. The polymerase III holoenzyme binds to template DNA as a part of a multi protein complex that consists of several polymerase accessory factors. DNA polymerase synthesizes DNA only in the 5 ' to 3 ' direction and only one of the several different types of polymerases is involved at the replication fork. As the DNA strands are anti parallel, the DNA polymerase functions asymmetrically. On the leading (forward) strand, the DNA is synthesized continuously. On the lagging strand (retro strand) the DNA is synthesized in short (1-5 kb) fragments. These DNA fragments are called as okazaki fragments. The proof function identifies copying errors and corrects them. Polymerase III is an enzyme with high processivity and catalysing capacity than others. The initiation of DNA synthesis requires priming by a short length of RNA about 10-200 nucleotides long. This priming process involves the nucleophilic attack by the 3' -OH group of the RNA primer on the aphosphate of the deoxyribonucleotide triphosphate that enters first,...
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