Introduction

• During interphase, the cell undergoes normal growth processes while also preparing for cell division.

• In order for a cell to move from interphase into the mitotic phase, many internal and external conditions must be met.

G1 Phase

• G1 phase: the cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus.

• Little change is visible.

S Phase

• S Phase: DNA replication occurs and forms identical pairs of DNA molecules—sister chromatids—that are firmly attached to the centromeric region.

• The centrosome is duplicated

  • The two centrosomes will give rise to the mitotic spindle

    • Mitotic spindle: the apparatus that orchestrates the movement of chromosomes during mitosis

• At the center of each animal cell, the centrosomes of animal cells are associated with a pair of rod-like objects, the centrioles, which are at right angles to each other.

• Centrioles help organize cell division.

• Centrioles are not present in the centrosomes of other eukaryotic species, such as plants and most fungi.

G2 Phase

• G2 phase: the cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation.

• There may be additional cell growth