Final answer:
The first phase of interphase is the G1 phase, where the cell grows and gathers resources for DNA synthesis. Cyclins bind to CDKs and regulate the cell cycle, ensuring proper progression to the S phase for DNA replication.
Step-by-step explanation:
First Phase of Interphase and the Role of Cyclin
The first phase of interphase in the cell cycle is known as the G1 phase (first gap). During this phase, the cell is metabolically active, increasing in size, and preparing the necessary components for DNA synthesis. It accumulates the building blocks of chromosomal DNA, associated proteins, and enough energy reserves to replicate each chromosome in the nucleus. The importance of cyclin during the G1 phase lies in its role in regulating the cell cycle. Cyclins are proteins that bind to enzymes called cyclin-dependent kinases (CDKs). This binding is crucial for the cell to pass the G1 checkpoint and transition into the S phase, during which DNA replication occurs. Without adequate levels of cyclin, CDKs remain inactive, thus preventing the cell from progressing to the next stage of the cell cycle, ensuring that cell division is carried out accurately and effectively.
The first stage of interphase is called the G1 phase (first gap) because, from a microscopic aspect, little change is visible. However, during the G1 stage, the cell is quite active at the biochemical level. The cell is accumulating the building blocks of chromosomal DNA and the associated proteins as well as accumulating sufficient energy reserves to complete the task of replicating each chromosome in the nucleus.