Answer:
true
Step-by-step explanation:
Scientists have devoted decades of effort to understanding how deoxyribonucleic acid (DNA) replicates itself. In simple terms, replication involves use of an existing strand of DNA as a template for the synthesis of a new, identical strand. American enzymologist and Nobel Prize winner Arthur Kornberg compared this process to a tape recording of instructions for performing a task: "[E]xact copies can be made from it, as from a tape recording, so that this information can be used again and elsewhere in time and space" (Kornberg, 1960).
In reality, the process of replication is far more complex than suggested by Kornberg's analogy. Researchers typically utilize simple bacterial cells in their experiments, but they still do not have all the answers, particularly when it comes to eukaryotic replication. Nonetheless, scientists are familiar with the basic steps in the replication process, and they continue to rely on this information as the basis for continued research and experimentation.
The Molecular Machinery of Bacterial DNA Replication
A typical bacterial cell has anywhere from about 1 million to 4 million base pairs of DNA, compared to the 3 billion base pairs in the genome of the common house mouse (Mus musculus). Still, even in bacteria, with their smaller genomes, DNA replication involves an incredibly sophisticated, highly coordinated series of molecular events. These events are divided into four major stages: initiation, unwinding, primer synthesis, and elongation.
Initiation and Unwinding
During initiation, so-called initiator proteins bind to the replication origin, a base-pair sequence of nucleotides known as oriC. This binding triggers events that unwind the DNA double helix into two single-stranded DNA molecules. Several groups of proteins are involved in this unwinding (Figure 1). For example, the DNA helicases are responsible for breaking the hydrogen bonds that join the complementary nucleotide bases to each other; these hydrogen bonds are an essential feature of James Watson and Francis Crick's three-dimensional DNA model. Because the newly unwound single strands have a tendency to rejoin, another group of proteins, the single-strand-binding proteins, keep the single strands stable until elongation begins. A third family of proteins, the topoisomerases, reduce some of the torsional strain caused by the unwinding of the double helix.
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