Final answer:
The p53 protein, activated by ATM kinase and Chk2 in response to DNA damage, separates from Mdm2 and halts the cell cycle at the G₁ checkpoint to enable DNA repair or induce apoptosis if repair is not possible.
Step-by-step explanation:
The p53 protein is a crucial component in the cellular response to DNA damage and stress. It is activated and stabilized by ATM (a kinase) and Chk2 in response to such events. The ATM kinase phosphorylates Mdm2, leading to its dissociation from p53 and allowing p53 to function. Subsequently, ATM activates Chk2, while free p53 gets phosphorylated as well. This activation results in the separation of the p53-Mdm2 complex, enabling p53 to effectively act as a checkpoint in the cell cycle.
Within the cell, p53, along with proteins like Rb and p21, primarily functions at the G₁ checkpoint. When DNA damage is detected, p53 works to halt the cell cycle and recruits specific enzymes for DNA repair. The protein also induces the production of p21, which helps to enforce the cell cycle arrest by inhibiting the Cdk/cyclin complexes. If the repair is not possible, p53 can initiate apoptosis through the intrinsic pathway, avoiding the propagation of damaged DNA.
Therefore, the correct statement to fill in the blanks is 'The p53 protein pathway is activated and stabilized by ATM and Chk2 in response to DNA damage to arrest the cell cycle and allow DNA repair to occur, but can also induce apoptosis through the intrinsic pathway.'