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Interphase refers to the ‘metabolic phase’ where the cell grows, replicates its DNA, and prepares for mitosis (division of the nucleus). It is one of the phases of the cell cycle that occupies around 95% time of the overall cycle.
- Interphase is also known as the resting phase.
- Cell cycle refers to a series of events that occur during the life of a cell.
- A typical cell spends most of its life in the ‘metabolic phase’ or interphase.
- In this phase, the cell prepares for division through DNA replication and cell growth.
- Cells in interphase undergo the synthesis of proteins and the transcribing of DNA into RNA.
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Key Terms: Interphase, Stages of Interphase, Cell Division, Cell Cycle, Cells, DNA Replication, RNA, Mitosis, Nucleus, S Phase
Interphase
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Interphase is the preparatory phase for cell division, where the cell prepares for mitosis or meiosis of the nucleus. It is the longest phase in the cell cycle and takes place in the cytoplasm and nucleus.
- The duration of time spent in interphase depends upon the type of cell and the species of organism.
- Aside from undergoing metabolic reactions, the cell also replicates its DNA.
- Interphase can be used to repair DNA double-strands.
- G1 Phase, S Phase and G2 Phase are three phases of interphase.
- It also undergoes a quiescent stage, where cells are not further divided and remain inactive.
Interphase
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Stages of Interphase
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The interphase is divided into three phases which are as follows:
G1 Phase (Gap 1)
G1 Phase is the first stage of interphase, which occurs between the initiation of replication of the cell's genetic material and mitosis. During this stage, the cell synthesizes high levels of protein and carries out normal functions related to cell growth.
- The cell expands its size and volume due to the production of cell organelles.
- The cell needs to produce a large quantity of ribosomes to prepare itself for the later stages.
- Basically, the cell creates the molecular building blocks during the G1 phase.
- After this phase is completed, the cell's mitochondria become part of a larger network to produce energy effectively.
S Phase (Synthesis)
The S phase is one of the important stages of interphase as it involves DNA replication. Semiconservative replication also occurs during this phase, during which the number of chromosomes remains constant.
- Along with DNA duplication, the cell also duplicates a microtubule-organizing structure called the centrosome.
- It helps in separating the DNA during the M phase.
- To make DNA stable, copies of DNA are created with packaged proteins called histones wrapped around them.
- Phospholipids, which constitute the membranes of cell and cell organelles, are also synthesized during the S phase.
G2 Phase (Gap 2)
The G2 phase is the stage where the cell is prepared to undergo mitosis. During this phase, proteins, RNA, lipids and macromolecules are required for the multiplication of cell organelles.
- The G2 phase involves the division of mitochondria and chloroplast for nucleus division.
- In this process, the cell continues its growth processes and synthesizes more proteins and organelles while preparing itself for cell division.
- The number of discrete organelles also increases during this phase.
Stages of Interphase
Things to Remember
- Interphase in a cell is that part of a cell's growth where several metabolic reactions take place.
- It comprises three stages: G1, S Phase and G2.
- Additionally, there is also a G0 phase for cells that do not undergo cell division.
- In the G1 phase, the cell grows and synthesizes ribosomes to prepare for the later stages.
- In the synthesis phase, the cell replicates its DNA.
- In the G2 phase, the cell continues with its growth.
- Two checkpoints exist to monitor cell division and prevent damaged cells from replicating.
- Interphase happens differently in different cells.
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Sample Questions
Ques. What is interphase? (2 marks)
Ans. The life of a cell involves a cycle of cell growth and cell division. Interphase is that phase of cell growth where multiple metabolic activities occur. It is the resting phase of cell cycle, in which the cell waits before undergoing mitosis to perform cell division.
Ques. What are the phases of interphase? (2 marks)
Ans. Interphase has three main phases, namely, G1, S and G2. In G1 phase, the cell displays physical growth by accumulating protein and organelles. In S phase, a cell replicates its DNA and centrosome. The cell continues with its growth processes and synthesizes more proteins and organelles while also preparing itself for cell division during G2 phase.
Ques. What is M Phase? (3 marks)
Ans. During the mitotic (M Phase), the cell divides its duplicated DNA and cytoplasm to make two new daughter cells.
- M Phase involves two division-related processes: mitosis and cytokinesis
- During mitosis, the nuclear DNA of the cell is broken down into visible chromosomes and is separated by the mitotic spindle.
- During cytokinesis, the cytoplasm of the cell divides to create two new daughter cells.
Ques. Why is interphase important in cell division? (2 marks)
Ans. Interphase is crucial for cell division because it enables the cell to develop, repeat its DNA, and complete the last preparations for mitosis—cell division. The G1 phase is characterized by the cell's growth, function, and physical enlargement. The S phase is when DNA replication occurs in the cell.
Ques. What is the role of interphase in cell cycle? (3 marks)
Ans. The cell cycle comprises cell growth and cell division. Interphase plays an important role in a cell cycle by preparing the cell for cell division. Interphase facilitates the growth of a cell, helps in the synthesis of important proteins and organelles and the replication of DNA.
- Several external and internal conditions need to be met by the cell prior to mitosis.
- There also exists a unique stage called G0 which some cells undergo, which does not allow cell division.
- Cells which do not perform cell division stay in the G0 permanently.
Ques. What is centrioles? (2 marks)
Ans. Centrioles are tiny, barrel-shaped organelles found near the nucleus in most animal cells. They are made up of microtubules, which are tiny protein tubes that act like the cell's skeleton. They typically exist as a pair, arranged perpendicular to each other. Each centriole has a specific structure with nine triplets of microtubules organized in a cylindrical pattern.
Ques. What is the role of interphase in different cells? (3 marks)
Ans. Different cells have different kinds of interphase mechanisms. For example, a eukaryotic cell undergoes all the stages of interphase (Gap 1, Synthesis Phase and Gap 2).
- Cells that undergo cell division spend around 95% of their time in the interphase.
- Certain cells which do not undergo cell division remain permanently in the interphase, whereas more active cells like the skin cells must enter the interphase in order to synthesise all the necessary organelles.
- There also exist certain cells which do not undergo the process of interphase, like the bacterial cells as there is DNA replication occurring.
Ques. How does interphase perform controlling functions during cell division? (5 marks)
Ans. When Gap 1 is completed, a checkpoint known as G1/S scrutinises the cell in order to verify if it is fit to go for DNA replication. At this step, damages or errors in the DNA are checked to ensure that cell replication thrives.
- A mechanism called molecular switching takes place during which multiple proteins interact with DNA.
- This process continues to take place throughout the entire duration of the S phase.
- If certain cells are found to be damaged or erroneous, they undergo apoptosis or programmed cell death.
- A second checkpoint is present at the G2 phase, after the synthesis of DNA in the S phase, during which kinase enzymes are used to control various processes in cell division cycles.
- Uncontrolled cell mutation may lead to carcinogenesis or development of tumors.
- Furthermore, in case the cell misses to go through the second checkpoint, cancer cells may develop.
Ques. Why is interphase called resting phase? (2 marks)
Ans. Since there is no cell division during interphase, it was referred to as the resting state. Subsequent research demonstrated that a cell's interphase is highly metabolically active. There are three subphases in interphase: G1, G2, and S. S-phase is when DNA synthesis takes place.
Ques. What are four stages of M Phase? (2 marks)
Ans. The four stages of M phase are as follows:
- Prophase
- Metaphase
- Anaphase
- Telophase
Ques. What are the characteristics of interphase? (3 marks)
Ans. The characteristics of interphase are as follows:
- During interphase, chromosomes are in the diffused and coiled stage.
- The amount of DNA is doubled during the replication phase.
- There is no damage to the nuclear membrane.
- The size of the nucleolus increases during rRNA synthesis.
- The cells are used for the synthesis of proteins, lipids, and membranes.
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