Question

Match the correct set.

A. CdK${}_4$	1. First growth phase
B. S phase	2. Differential phase
C. G${}_0$ phase	3. Synthesis of tublin
D. G${}_2$ phase	4. Replication of DNA
	5. Molecule active during G${}_1$phase for protein synthesis

• A. A - 3, B - 4, C - 2, D - 1
• B. A - 1, B - 2, C - 3, D - 4
• C. A - 5, B - 3, C - 2, D - 1
• D. A - 5, B - 4, C - 2, D - 3

Answer 1

The correct option is D A - 5, B - 4, C - 2, D - 3

• DNA replication occurs during the synthesis or S phase.
• Non-proliferative cells in multicellular eukaryotes generally enter the quiescent $G_0$ state from $G_1$and may remain quiescent for long periods of time, possibly indefinitely (as in the case of neurons). Thus, $G_0$ is also called a differential stage.
• Tubulin proteins are used in spindle formation and synthesized in G${}_2$ phase.
• The events of the cell cycle are tightly regulated. Two key classes of regulatory molecules, cyclins and cyclin-dependent kinases (CDKs), determine a cell's progress through the cell cycle. Cyclin D binds to existing CDK4, forming the active cyclin D-CDK4 complex during $G_1$ phase, so that cell can successfully enter $S$ phase.