Question

How can disruption of the cell cycle result in cancer?

Answer 1

Cancer is a disease caused by the abnormal and uncontrollable division of the cells. This occurs when the normal functioning mechanism of the body stops working.

Complete answer:
The sequence of events that occurs in a cell prior to its division is called the cell cycle. It has four main stages- $G_1$ phase, S phase, $G_2$ phase, and the division or M phase. The first three phases are collectively called the Interphase. Major events occurring in the stages of eukaryotic cell division are-
$G_1$ phase/ Gap 1 phase/ Growth 1 phase- In this phase, the size of the cell increases, and proteins and RNA required for the synthesis of DNA is formed. The cells from this stage can also go to a state of dormancy or Go phase.
S phase/ Synthesis phase- In this phase, the synthesis or replication of DNA occurs inside the nucleus of a cell. It is the longest and the most regulated phase of the interphase.
$G_2$ phase/ Gap 2 phase/ Growth 2 phase- In this phase, the cell prepares itself for the division. The growth of the cell occurs along with the formation of proteins.
M phase/ Mitotic phase/Division phase- A fully grown cell divides to form 2 daughter cells.
A eukaryotic cell cycle has few checkpoints where the cell checks if it should proceed to the next stage or not. They are-

$G_1$ checkpoint- Only the cells that have undergone sufficient growth and have the desired proteins for the replication of DNA cross this checkpoint.
$G_2$ checkpoint- It checks the integrity of the DNA. If the DNA is anyhow damaged or not replicated, the cell does not undergo mitotic division.
Spindle checkpoint- It checks the attachment of the chromosomes to the spindle apparatus.
In a normal cell, the cell cycle is controlled by a series of signaling pathways, proteins, enzymes, inhibitors, and checkpoints. If errors are found during the checkpoints, they are either corrected, or the cells undergo programmed cell death called- apoptosis.

Cancerous cells divide rapidly and spread to the surrounding tissues. The old cells do not die and form abnormal cells that may form a mass of tissue called- tumors. These cells are also capable of destroying the body tissues. Tumors are of two types- Benign and Malignant.
An abnormal cell cycle may lead to cancer. If the checkpoints are missing or not working, the cells will undergo an uncontrollable and unregulated growth, and their DNA will not be checked. Any mutation or error in their DNA will be inherited in the new cells.

The inhibitors limit the process of division and regulators promote this process. In the absence of inhibitors or over productivity of regulators, the cells will have an uncontrollable growth. The mutation in these proteins can also alter their function. The tumor formed due to the uncontrollable division of cells is called a Malignant tumor.

Note: Benign tumors- lacks the ability to spread or invade other tissues. Whereas, malignant tumors can spread and invade other tissues. They can also recover after they are removed from the specific organ. Their uncontrollable growth can be life-threatening.