PATHOLOGY

Detailed explanation-1: -1. The protein that is maintained at constant levels throughout the cell cycle that requires cyclin to become catalytically active is CDK. Explanation: CDK stands for cyclin-dependent kinase.

Detailed explanation-2: -Which of the following is a protein maintained at constant levels throughout the cell cycle that requires cyclin to become catalytically active? cyclins.

Detailed explanation-3: -Although levels of Cdks remain constant throughout the cell cycle, the activitiy of Cdks oscillate due to cell cycle-dependent phosphorylation and changes in the amounts of cyclins. In addition, the ubiquitin-mediated degradation of cyclins is critical for proper cell cycle progression.

Detailed explanation-4: -For example, yeast have only a single CDK, whereas vertebrates have four different ones. As their name suggests, CDKs require the presence of cyclins to become active. Cyclins are a family of proteins that have no enzymatic activity of their own but activate CDKs by binding to them.

Detailed explanation-5: -The formation of cyclin/CDKs controls the cell-cycle progression via phosphorylation of the target genes, such as tumor suppressor protein retinoblastoma (Rb). The activation of cyclins/CDKs is induced by mitogenic signals and inhibited by the activation of cell-cycle checkpoints in response to DNA damage [8].