AP BIOLOGY

Detailed explanation-1: -Eukaryotic DNA replication is regulated to ensure all chromosomes replicate once and only once per cell cycle. Replication begins at many origins scattered along each chromosome. Except for budding yeast, origins are not defined DNA sequences and probably are inherited by epigenetic mechanisms.

Detailed explanation-2: -The division cycle of most eukaryotic cells is divided into four discrete phases: M, G1, S, and G2. M phase (mitosis) is usually followed by cytokinesis. S phase is the period during which DNA replication occurs.

Detailed explanation-3: -The preparation for DNA replication initiation is tightly linked to cell-cycle progression, ensuring that replication occurs only once per cycle. The time is ripe for a molecular dissection of the links between the two processes.

Detailed explanation-4: -S phase. In S phase, the cell synthesizes a complete copy of the DNA in its nucleus. It also duplicates a microtubule-organizing structure called the centrosome.

Detailed explanation-5: -Initiation of replication occurs only once per cell division cycle, and simultaneously at all origins present in a cell (Skarstad et al., 1986).