Question

at which checkpoint does the cell assess whether dna replication has been completed accurately?
s checkpoint
g1 checkpoint
g2 checkpoint
m checkpoint
what are the two key players in regulating the cell cycle?
cyclins and checkpoints
growth factors and hormones
dna replication and p53
cdks and dna repair

Explanation:

• First question:
• The \(G2\) checkpoint occurs after the \(S\) phase (where DNA replication happens). Its main role is to check if DNA replication has been completed accurately before the cell enters mitosis (\(M\) phase).
• The \(S\) checkpoint monitors DNA replication as it is occurring. The \(G1\) checkpoint checks for cell size, nutrients, growth factors, and DNA damage before the cell enters the \(S\) phase. The \(M\) checkpoint (spindle - assembly checkpoint) checks for proper attachment of chromosomes to the spindle fibers during mitosis.
• Second question:
• Cyclins are proteins that regulate the cell cycle by activating cyclin - dependent kinases (\(CDKs\)). Checkpoints are control points in the cell cycle that ensure the cell meets certain requirements (like DNA integrity, proper cell size) before progressing to the next phase.
• Growth factors and hormones can influence the cell cycle but are not the key regulatory "players" in the sense of directly controlling the progression through the cell - cycle phases like cyclins and checkpoints. DNA replication is a process in the cell cycle, and \(p53\) is a tumor - suppressor protein involved in DNA repair and cell - cycle arrest (but not one of the two main regulators asked about). \(CDKs\) need cyclins to be activated, and DNA repair is a mechanism rather than a key regulatory "player" in the overall cell - cycle regulation as presented in the options.

Answer:

• First question: G2 checkpoint
• Second question: Cyclins and Checkpoints