6.2
Interphase
In eukaryotic cells, the largest portion of the cell cycle is interphase, which is divided into three stages, G1, S, and G2. In G1, the first gap phase, a newly generated daughter cell grows in size and prepares for DNA duplication in the next phase.
Now, in S, the synthesis phase, cells duplicate their nuclear DNA, which remains packaged as chromatin. Cells also duplicate the centrosomes, the microtubule organizing structure which form the mitotic spindle apparatus. Finally, in G2, the second gap phase, cells continue to grow, multiply organelles and proteins that are required for mitosis and replenish their energy stores. The cell is now ready to enter the first stage of mitosis.
The cell cycle occurs over approximately 24 hours (in a typical human cell) and in two distinct stages: interphase, which includes three phases of the cell cycle (G1, S, and G2), and mitosis (M). During interphase, which takes up about 95 percent of the duration of the eukaryotic cell cycle, cells grow and replicate their DNA in preparation for mitosis.
Phases of Interphase
Following each period of mitosis and cytokinesis, eukaryotic cells enter interphase, during which they grow and replicate their DNA in preparation for the next mitotic division.
During the G1 (gap 1) phase, cells grow continuously and prepare for DNA replication. During this phase, cells are metabolically active and copy essential organelles and biochemical molecules, such as proteins.
In the subsequent S (synthesis) phase of interphase, cells duplicate their nuclear DNA, which remains packaged in semi-condensed chromatin. During the S phase, cells also duplicate the centrosome, a microtubule-organizing structure that forms the mitotic spindle apparatus. The mitotic spindle separates chromosomes during mitosis.
In the G2 (gap 2) phase, which follows DNA synthesis, cells continue to grow and synthesize proteins and organelles to prepare for mitosis.
In human cells, the G1 phase spans approximately 11 hours, the S phase takes about 8 hours, and the G2 phase lasts about 4 hours. During G1, cells are diploid (2n, a pair of each chromosome). Following replication in S phase, cells increase their DNA content to 4n. Cells remain 4n until cytokinesis, at which point their DNA content is reduced to 2n.
In eukaryotic cells, the largest portion of the cell cycle is interphase, which is divided into three stages, G1, S, and G2. In G1, the first gap phase, a newly generated daughter cell grows in size and prepares for DNA duplication in the next phase.
Now, in S, the synthesis phase, cells duplicate their nuclear DNA, which remains packaged as chromatin. Cells also duplicate the centrosomes, the microtubule organizing structure which form the mitotic spindle apparatus. Finally, in G2, the second gap phase, cells continue to grow, multiply organelles and proteins that are required for mitosis and replenish their energy stores. The cell is now ready to enter the first stage of mitosis.
- Cell Cycle – Series of stages a cell undergoes to grow, replicate DNA, and divide into two daughter cells.
- Interphase – Longest cell cycle phase where cells grow, replicate DNA, and prepare for mitosis.
- G1 Phase – First growth phase marked by active metabolism and organelle duplication.
- S Phase – Phase when DNA is replicated and centrosomes are duplicated for cell division.
- G2 Phase – Final interphase stage with continued growth and protein synthesis before mitosis.
- Define Interphase Phases – Recognize the G1, S, and G2 stages where cells grow, replicate DNA, and prepare for mitosis (e.g., cell cycle).
- Understand DNA Replication – Learn how DNA strands are duplicated during the S phase using semiconservative synthesis (e.g., synthesis).
- Track Cell Growth – Identify key processes in G1 and G2 like organelle duplication and protein synthesis before mitosis (e.g., growth).
- Compare DNA Content – Follow chromosome duplication from diploid (2n) to tetraploid (4n) and return to 2n after cytokinesis.
- Prepare for Mitosis – Understand interphase as a foundation for cell division.
- What is interphase in the cell cycle and why is it essential for cell division?
- What happens in the S phase of the interphase and why is DNA replication important?
- What happens during the G2 phase of interphase and how does it prepare the cell for mitosis?
From Chapter 6:
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