"DNA Replication - Download as DOC"
DNA Replication 1. The double strand of DNA unzips like a zipper 2. Free-floating nucleotides match with their compliments and connect along the backbone 3. Thus, a new strand is formed along each of the open strands. In this way, a single DNA molecule becomes two. Enzymes that copy DNA - Initiator protein: finds the place to begin copying and guides the unzipper to the correct position - Topoisomerase: untwists the DNA double helix - Helicase: the unzipper separates the DNA strands by breaking the weak bonds between the nucleotides - Single-strand DNA binding proteins: keep the single strands of DNA from getting tangled - Polymerases: the builders assemble a new DNA strand along each of the exposed strands. They build by joining individual nucleotides to their matching compliments on the old strand. The free floating nucleotides bring their own energy. Remember ATP? There’s also GTP, CTP, and TTP. As the nucleotide is added to the growing chain its phosphate bond energy goes into making the new bond. i. The upper polymerase follows behind the helicase, but the lower builder must build in short lengths ii. The short lengths, called Okazaki fragments, are spliced together by ligase - Repair nuclease: find poorly matching or damaged nucleotides and snip them out - Polymerase: follow close behind to fill the gaps - Ligase: restore the continuity of the backbone of the repaired strand