THE MOLECULAR BASIS OF INHERITANCE
DNA REPLICATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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DNA polymerase I must create a base for it to start at
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Primase lays down thymine and cytosine
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DNA polymerase III doesn’t need any help
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Primase lays down RNA primers
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Detailed explanation-1: -Primase synthesizes RNA primers complementary to the DNA strand. DNA polymerase III extends the primers, adding on to the 3’ end, to make the bulk of the new DNA. RNA primers are removed and replaced with DNA by DNA polymerase I. The gaps between DNA fragments are sealed by DNA ligase .
Detailed explanation-2: -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-3: -These primers serve as a starting point for DNA synthesis. The synthesis of a primer is necessary because the enzymes that synthesize DNA, which are called DNA polymerases, can only attach new DNA nucleotides to an existing strand of nucleotides.
Detailed explanation-4: -An RNA primer is a short segment of single-stranded RNA used as a binding site for DNA polymerase to initiate DNA replication. DNA polymerase is only able to add nucleotides to an existing nucleotide chain; it cannot “start from scratch, ” and therefore needs the RNA primer to start the process.
Detailed explanation-5: -The main function of the third polymerase, Pol III, is duplication of the chromosomal DNA, while other DNA polymerases are involved mostly in DNA repair and translesion DNA synthesis. Together with a DNA helicase and a primase, Pol III HE participates in the replicative apparatus that acts at the replication fork.