Requirements of Replication

Although the process of replication includes many components, they can be combined into three major groups:

  1. A template consisting of single-stranded DNA

  2. Raw materials (substrates) to be assembled into a new nucleotide strand

  3. Enzymes and other proteins that “read” the template and assemble the substrates into a DNA molecule

Because of the semiconservative nature of DNA replication, a double-stranded DNA molecule must unwind to expose the bases that act as a template for the assembly of new polynucleotide strands, which will be complementary and antiparallel to the template strands.

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The raw materials from which new DNA molecules are synthesized are deoxyribonucleoside triphosphates (dNTPs), each consisting of a deoxyribose sugar and a base (a nucleoside) attached to three phosphate groups (Figure 9.6a). In DNA synthesis, nucleotides are added to the 3′-hydroxyl (3′-OH) group of the growing nucleotide strand (Figure 9.6b). The 3′-OH group of the last nucleotide on the strand attacks the 5′-phosphate group of the incoming dNTP. Two phosphate groups are cleaved from the incoming dNTP, and a phosphodiester bond is created between the two nucleotides.

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Figure 9.6: New DNA is synthesized from deoxyribonucleoside triphosphates (dNTPs). The newly synthesized strand is complementary and antiparallel to the template strand; the two strands are held together by hydrogen bonds (represented by red dotted lines) between the bases.

DNA synthesis does not happen spontaneously. Rather, it requires a number of enzymes and proteins that function in a coordinated manner. We will examine this complex array of proteins and enzymes in Section 9.3 as we consider the replication process in more detail.

CONCEPTS

DNA replication requires a single-stranded DNA template, deoxyribonucleoside triphosphates, a growing nucleotide strand, and a group of enzymes and proteins.