INTERFACE: DURATION AND PHASES - BIOLOGY - 2024

The interface is a stage where cells grow and develop, taking nutrients from the external environment. Generally, the cell cycle is divided into interface and mitosis.

The interface is equivalent to the "normal" stage of the cell, where genetic material and cellular organelles replicate and the cell prepares itself in various respects for the next stage of the cycle, mitosis. It is the phase where cells spend most of their time.

Source: File: Cytokinesis eukaryotic mitosis.svg: LadyofHatsderivative work: Chabacano, via Wikimedia Commons

The interface consists of three subphases: phase G ₁, which corresponds to the first interval; the S phase, of synthesis and the G ₂ phase, the second interval. At the conclusion of this stage, the cells go into mitosis, and the daughter cells continue the cell cycle.

What is the interface?

The "life" of a cell is divided into several stages, and these comprise the cell cycle. The cycle is divided into two fundamental events: interface and mitosis.

During this stage, cell growth and chromosome copying can be observed. The objective of this phenomenon is the preparation of the cell to divide.

How long does it last?

Although the temporal length of the cell cycle varies considerably between cell types, the interface is a long stage, where a significant number of events occur. The cell spends approximately 90% of its life at the interface.

In a typical human cell, the cell cycle can divide in 24 hours and would be distributed as follows: the mitosis phase takes less than an hour, the S phase takes about 11-12 hours - roughly half the cycle.

The rest of the time it is divided into phases G ₁ and G ₂. The latter would last in our example between four and six hours. For the G ₁ phase, it is difficult to assign a number, as it varies greatly between cell types.

In epithelial cells, for example, the cell cycle can be completed in less than 10 hours. In contrast, liver cells take longer, and they may divide once a year.

Other cells lose the ability to divide as the body ages, as is the case of neurons and muscle cells.

Phases

The interface is divided into the following sub-phases: G ₁ phase, S phase, and G ₂ phase. We will describe each of the stages below.

Phase G

The G ₁ phase is located between mitosis and the beginning of the replication of genetic material. At this stage, the cell synthesizes the necessary RNAs and proteins.

This phase is crucial in the life of a cell. Sensitivity increases, in terms of internal and external signals, which make it possible to decide if the cell is ready to divide. Once the decision to continue is made, the cell enters the rest of the phases.

S phase

The S phase comes from "synthesis". In this phase, DNA replication occurs (this process will be described in detail in the next section).

Phase G

The G ₂ phase corresponds to the interval between the S phase and the following mitosis. Here DNA repair processes take place, and the cell makes the final preparations to start the division of the nucleus.

When a human cell enters the G ₂ phase, it has two identical copies of its genome. That is, each of the cells has two sets of 46 chromosomes.

These identical chromosomes are called sister chromatids, and material is often exchanged during the interface, in a process known as sister chromatid exchange.

Phase G

There is an additional stage, G ₀. A cell is said to enter "G ₀ " when it stops dividing for a long period of time. At this stage, the cell can grow and be metabolically active, but DNA replication does not occur.

Some cells seem to have been trapped in this almost "static" phase. Among these we can mention the cells of the heart muscle, the eye and the brain. If these cells are damaged, there is no repair.

The cell enters the division process thanks to different stimuli, either internal or external. For this to occur, DNA replication must be accurate and complete, and the cell must be of adequate size.

Replication of DNA

The most significant and longest event of the interface is the replication of the DNA molecule. Eukaryotic cells present genetic material in a nucleus, delimited by a membrane.

This DNA must replicate in order for the cell to divide. Thus, the term replication refers to the duplication event of the genetic material.

Copying the DNA of a cell must have two very intuitive characteristics. First, the copy must be as accurate as possible, in other words, the process must show fidelity.

Second, the process must be fast, and the deployment of the enzymatic machinery necessary for replication must be efficient.

DNA replication is semi-conservative

For many years various hypotheses were put forward on how DNA replication could occur. It wasn't until 1958 that researchers Meselson and Stahl concluded that DNA replication is semi-conservative.

"Semiconservative" means that one of the two strands that constitutes the DNA double helix serves as a template for the synthesis of the new strand. In this way, the end product of replication is two DNA molecules, each one made up of an original chain and a new one.

How does DNA replicate?

DNA must undergo a series of complex modifications for the replication process to take place. The first step is to unroll the molecule and separate the chains - just like we unzip our clothes.

In this way, the nucleotides are exposed and serve as a template for a new strand of DNA to be synthesized. This region of DNA where the two chains separate and copy each other is called the replication fork.

All the mentioned processes are assisted by specific enzymes - such as polymerases, topoisomerases, helicases, among others - with diverse functions, forming a nucleoprotein complex.

References

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5. Rodak, BF (2005). Hematology: fundamentals and clinical applications. Panamerican Medical Ed.