G2 is the final stage of interphase, occurring after DNA replication. The cell shifts from copying genetic material to building the machinery, energy supply, and structural organisation required to separate chromosomes accurately during mitosis.

Where G2 fits in the cell cycle

G2 (Gap 2) occurs after S phase has duplicated the genome and before mitosis (M phase) begins.

This labeled cell-cycle diagram shows interphase subdivided into G1, S, and G2, followed by M phase, emphasizing that G2 is the final growth/preparation interval after DNA synthesis. The G0 branch highlights that cells can also exit the cycle into quiescence rather than proceeding into division. Source

During G2, the cell is typically larger than in G1 and is focused on readiness rather than genome copying.

Key idea: the genome is already replicated, so G2 prioritises protein synthesis, ATP availability, and centrosome replication to support mitotic spindle formation and chromosome movement.

Core specification features of G2

Protein synthesis: building mitotic machinery

A major requirement for mitosis is a rapid increase in proteins that will form and run the mitotic apparatus.

• Increased synthesis of microtubule subunits (especially tubulin) to build spindle fibres

• Production of motor proteins that move along microtubules (for chromosome transport and spindle dynamics)

• Synthesis of proteins that help condense chromatin and organise chromosomes for segregation

• Additional production of membrane and cytoskeletal proteins that support cell shape changes as mitosis begins

These proteins accumulate so the cell can transition quickly into prophase without pausing to manufacture core components.

Increased ATP production: powering mitosis

Mitosis is energy-demanding: microtubules constantly polymerise/depolymerise, motors generate force, and cellular architecture is reorganised. In G2, cells increase energy readiness by boosting ATP availability.

• Higher ATP production supports:

  • assembly and dynamics of the mitotic spindle

  • active transport of proteins to where they are needed

  • chromosome movement driven by motor proteins

  • overall metabolic activity associated with rapid structural reorganisation

This emphasis on ATP aligns with the specification: G2 includes increased ATP production to prepare for mitosis.

Centrosome replication: organising spindle poles

The cell must enter mitosis with two microtubule-organising centres so that a bipolar spindle can form.

• Centrosome replication (completion and maturation) occurs during late interphase so that:

  • there are two centrosomes available to serve as spindle poles

  • microtubules can be nucleated efficiently for spindle formation

• The centrosomes begin to separate as the cell approaches mitosis, supporting rapid spindle assembly once mitosis starts

This diagram summarizes the centrosome cycle, tracking centriole duplication and centrosome maturation as the cell progresses through interphase into mitosis. It visually reinforces how duplication and separation generate two spindle poles, which is essential for forming a bipolar mitotic spindle and ensuring accurate chromosome segregation. Source

A failure to produce or properly organise centrosomes risks abnormal spindle geometry and improper chromosome segregation.

Centrosomes help ensure chromosomes can be pulled toward opposite ends of the cell when division begins.

Cellular readiness tasks during G2 (high-yield details)

Although the specification highlights three major features, students should connect them to what “preparation for mitosis” functionally requires.

Structural and organisational preparation

• Expansion and reorganisation of the cytoskeleton to support spindle formation and changes in cell shape

• Positioning of duplicated components so they can be partitioned efficiently once mitosis starts

• Accumulation of key regulatory proteins needed for the cell to commit to mitotic entry (without focusing on checkpoint mechanics)

Quality control before mitosis (conceptual)

G2 is commonly associated with verifying that DNA replication has finished and that the cell is adequately prepared to divide. At an AP level, it is sufficient to understand that G2 supports orderly progression by ensuring resources and structures are in place before mitosis begins.

What to picture in a G2 cell

• DNA has been replicated; each chromosome consists of two identical DNA copies packaged for division later.

• The cell contains elevated levels of proteins needed for spindle construction and chromosome handling.

• ATP supply is ramped up to fuel upcoming mechanical work.

• Two centrosomes are available or nearing readiness, enabling rapid assembly of a bipolar spindle at mitotic entry.