How do normal cells and cancer cells differ in terms of cell-cycle regulation?

To answer this question, we first need to understand the cell cycle, which is the series of events that lead to cell growth and division. The cell cycle can be divided into four phases: G1 (gap 1), S (synthesis), G2 (gap 2), and M (mitosis).

Normally, cell-cycle progression is tightly regulated by proteins that ensure proper cell growth and division. Key regulatory components include cyclin-dependent kinases (CDKs), cyclins, and checkpoint proteins. Together, these proteins ensure that cells pass through each phase of the cell cycle only if the conditions for growth and division are met.

Cancer cells differ from normal cells in that their cell cycle regulation is defective, which results in uncontrolled growth and division. There are several reasons for this defect, including: 1- Mutations in the genes that encode checkpoint proteins: These mutations can cause the loss of function, meaning that cells can progress through the cell cycle even if conditions are not met for growth and division. 2- Overexpression of cyclins and CDKs: This can cause cells to divide more rapidly than normal, potentially leading to cancer formation. 3- Inactivation of tumor suppressor proteins: These proteins help maintain cell cycle regulation and prevent the formation of cancer cells. Cancer cells often have mutations in tumor suppressor genes, causing their inactivation and resulting in the loss of cell-cycle regulatory control.

As a result of these defects in cell cycle regulation, cancer cells grow and divide uncontrollably. This uncontrolled growth can lead to solid tumors, which can disrupt normal tissue function and potentially become malignant if allowed to spread to other parts of the body.

In summary, normal cells and cancer cells differ in terms of cell cycle regulation. While normal cells have tightly controlled regulation mechanisms involving CDKs, cyclins, and checkpoint proteins, cancer cells often possess defects that lead to a loss of control over the cell cycle. These defects can result in uncontrolled growth and division, leading to the formation and progression of cancer.