- The prokaryotic cell polymerizes 500 ucleotides/second. The eukaryotic cell synthesizes only 50 nucleotides/second. The eukaryotic cell, however, contains between four and five billion nucleotides! The prokaryotic cell chromosome is circular, and replication occurs efficiently. Eukaryotic cells employ the use of multiple replication bubbles, greatly speeding up replication. • Each replication bubble has two y-shaped replication forks. - DNA replication occurs at sites on the molecule called replication bubbles, and both strands are replicated simultaneously at a y-shaped structure called the replication fork. The position of the fork is constantly moving as replication proceeds. The illustrations on the left show replication bubbles and forks. - Synthesis of both complementary strands occurs in the 5’ to 3’ direction. The strand that is growing towards the replication fork grows continuously and is called the leading strand. Note that the newly formed leading strand is antiparallel to the parental strand that served as its template.

- continuous in one strand and discontinuous in the other. Events basic to the process of DNA replication and specific to the leading strand are discussed below

The overall events by which both strands are replicated are as follows:

1. Strands are separated and unwound by DNA helicase. 2. The strands are prevented from coming together by helix-destabilizing proteins. 3. The enzymes that catalyze the synthesis of the new complementary strands are called DNA polymerases. DNA polymerase can only add nucleotides to the 3’ end of the growing nucleotide strand. 4. RNA primer is required initiate synthesis of either new strand to provide the first 3’ end that the enzyme requires. The RNA primer is later removed and substituted with DNA.

During DNA synthesis, elongation of the leading strand:

- Depends on the action of DNA polymerase.

The purpose of multiple origins of replication is to

- speed up replication of eukaryotic chromosomes

The slow strand-synthesis rate in prokaryotes is overcome by:

- Prokaryotes actually have a relatively rapid strand synthesis rate

6.4.1 Events at the Replication Fork: The Leading Strand Flashcards by Irina Soloshenko

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6.4.1 Events at the Replication Fork: The Leading Strand Flashcards

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