Cell Cycle

The cell cycle is a series of events that occur during the life of a cell. Interphase, mitotic phase, and cytokinesis are the three stages that make up the eukaryotic cell cycle. Cell growth occurs during the interphase through the synthesis of needed proteins for the cell's subsequent stages, as well as the replication of DNA for cell division. The nucleus is divided into two genetically identical daughter nuclei during the mitotic phase, resulting in cell division. Cytokinesis is the division of the parent cell's cytoplasm.

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Stages of Cell Cycle 

A cell must perform many crucial activities in order to divide: it must grow, duplicate its genetic material (DNA), and physically split into two daughter cells. The cell cycle is a sequence of phases in which cells perform various functions in an orderly and predictable manner. The cell cycle is a cycle rather than a linear pathway because each daughter cell can also undergo the same processes.

There are two key phases in the cell cycle of eukaryotic cells, or cells containing a nucleus, namely, interphase and mitotic (M) phase.

• During interphase, the cell divides and duplicates its DNA.

• The cell splits its cytoplasm and divides its DNA into two sets during the mitotic (M) phase, resulting in the production of two new cells.

Cell Cycle Interphase

Let's start the cell cycle from the beginning when a cell divides from its mother cell. There are mainly three steps to prepare for division, as discussed below.

G₁ Phase

The cell becomes physically larger, duplicates organelles, and makes the chemical building blocks that will be needed in later processes during the G₁ phase, also known as the first gap phase.

S Phase

The cell synthesizes a full copy of DNA in its nucleus during the S phase. The centrosome, a microtubule-organizing structure, is also copied. During the M phase, the centrosomes assist in the separation of DNA.

G₂ Phase

The cell grows, produces proteins and organelles, and begins to restructure its contents in preparation for mitosis during the second gap phase, or G₂ phase. When mitosis commences, phase G₂ comes to an end.

Interphase is the combination of the G₁, S, and G₂ phases. The prefix inter-means between, reflecting the fact that interphase occurs between mitotic (M) phases.

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M Phase

During the mitotic (M) phase, the cell divides its copy DNA and cytoplasm to generate two new cells. During the M phase, two distinct division-related mechanisms occur mitosis and cytokinesis.

Mitosis

During mitosis, the cell's nuclear DNA condenses into visible chromosomes, which are pulled apart by the mitotic spindle, a specialised structure made up of microtubules. Mitosis is divided into four stages: prophase (sometimes known as early prophase and prometaphase), metaphase, anaphase, and telophase.

Cytokinesis

During cytokinesis, the cell's cytoplasm is split in half, resulting in the production of two new cells. Cytokinesis usually begins immediately as mitosis is concluding, with a little overlap. Importantly, cytokinesis happens in different ways in animal and plant cells.

Cell division occurs in mammals when the contractile ring, a band of cytoskeletal fibres, contracts inward and pinches the cell in half, a process known as contractile cytokinesis. The cleavage furrow is the indentation created as the ring contracts inward. As animal cells are delicate and squishy, they can be pinched in half.

Plant cells are substantially stiffer than animal cells, with a strong cell wall surrounding them and high internal pressure. Plant cells divide in half as a result of this, with a new structure forming in the middle of the cell. The cell plate is a structure that divides the cell in two and is made up of plasma membrane and cell wall components transported in vesicles. Plant cells have a stiff cell wall and a high internal pressure, making them much tougher than animal cells. As a result, cytokinesis happens differently in plant and animal cells.

Duration of the Cell Cycle

The cell cycle takes varying amounts of time for different cells. While a typical human cell divides in roughly 24 hours, fast-cycling mammalian cells, such as those that line the gut, can complete a cycle in as little as 9-10 hours when cultivated in vitro. Different cell types divide their time between cell cycle phases in various ways. For example, in early frog embryos, cells spend very little time in G₁ and G₂, preferring instead to cycle quickly between S and M phases, resulting in the division of one large cell, the zygote, into many smaller cells.

Some of the important differences between cell cycle and cell division are tabulated below.

What is the Difference Between Cell Cycle and Cell Division?

Did you Know?

• Which is the Longest Cell Phase? 

The longest cell phase is interphase, during which the cell goes through regular growth processes while also preparing for cell division. It is the longest phase of the cell cycle, with the cell spending over 90% of its time here.