Question

Compare and contrast the roles of the positive cell-cycle regulators negative regulators.

Short answer

Positive regulators helps in the progression of cell cycle while negative regulators inhibit the processes of cell cycle.

Step-by-step solution

Given information

In addition to the cell cycle checkpoints, there are two groups of intracellular substances that control the cell cycle.

These regulatory substances either help in the progression of the cell to the next phase (positive regulation) or halt the cycle (negative regulation) to inhibit proceeding further. These regulators may act individually, or they also can influence the activity or abundance of other regulatory proteins.

Explanation

Positive Regulation of the Cell Cycle

Two groups of proteins, namely cyclins and cyclin-dependent kinases (Cdks), are the positive regulators of cell cycle. They help in the cell progression through the checkpoints.

• Cyclins: Concentrations of cyclins fluctuate throughout the cell cycle. Ithelps to regulate the cell cycle by phosphorylating different significant proteins.
• Cyclin-dependent kinases (Cdks): Upon binding with Cdks it helps to regulate the cell cycle. It also shows phosphorylation of other proteins. By phosphorylation the proteins are either activated or inactivated.

Negative Regulation of the Cell Cycle

The second group of cell-cycle regulators are the negative regulators, which prevents the cell cycle to proceed further. The three well-known negative regulatory molecules are- retinoblastoma protein (Rb), p53, and p21.

• Retinoblastoma protein (Rb): It interacts with the E2F transcription factor and thus exhibits negative regulations on the cell cycle.
• p53:It is a regulatory protein that regulates cell growth and checks for DNA damage. It can halt the cell cycle progression if there is any damaged DNA and may also execute apoptosisif necessary.
• p21:This regulatory protein is controlled by p53 , thus also inhibits the cell cycle.