Cell Cycle & Cell Division - Cell Cycle & Checkpoint
Download My App just search - Gujarat Biology NEET PLUS on google play store
Link 👇
CELL CYCLE
- Cell cycle is a series of events by which a cell duplicates its genome, synthesises other constituents of the cell and eventually divides into two daughter cells.
- In a typical eukaryotic somatic cell, cell cycle has two main phases- a long non-dividing interphase (I-phase) and a short nucleus dividing mitotic phase (M-phase).
- Interphase is metabolically active phase and is divided into first gap phase or G1-phase, synthetic phase or S-p DNA synthesis hase and second gap phase or G2-phase.
- G1 phase : This phase is in between the end of M-phase of previous cell cycle and initiation of S-phase. It is the longest phase of interphase. In this phase, cell grows in size and RNA and proteins are synthesised. Cell organelles also increase in number. From G, phase, cells may enter into S-phase or sometimes in Go phase.
- S-phase : During this phase DNA synthesis takes place. DNA content becomes double, though the ploidy level remains same. Histone proteins are synthesised during S-phase.
- G2 phase : In this phase, synthesis of DNA stops, however, formation of RNAS and proteins continues which are required for multiplication of cell organelles, spindle formation, aster formation and cell growth. In animal cells, centrosome begins to divide and there is an extensive synthesis of tubulin protein to form microtubules.
- M-phase is divided into -karyokinesis or the division of nucleus followed by cytokinesis or the division of cytoplasm. Karyokinesis in again divisible into - prophase, metaphase, anaphase and telophase.
- Go phase is a period in the cell cycle in which cells exists in a quiescent state. Go phase is viewed either as an extended G, phase, where the cell is neither dividing nor preparing to divide or a distinct quiescent stage that occurs outside the cell cycle.
Cell Cycle Checkpoints
- Two key classes of regulatory molecules, cyclins and cyclin dependent protein kinases (CDKS) determine a cell's progress through the cell cycle.
- Cell cycle checkpoints are the control mechanisms that ensure the fidelity of cell division. There are two regulatory mechanisms which takes decision about cell division.
- First checkpoint is called G1 cyclin (CG1 or Gj/S) which is present in between G, and S phase. In G1, CDK becomes active by Gj cyclin and ATP at its activation site. It causes transition of G, to S phase. Gj cyclin is destroyed at the end of S-phase and CDK becomes inactive.
- Second checkpoint is present between G2 and M-phase. During G2 phase, inactive CDK binds to mitotic cyclin (CM or Gz/M). It gets phosphorylated at its both activation and inhibitory sites but still remains inactive. On removal of PO4 from the inhibitory site, it becomes active and causes transition from G, to M-phase. At the end of M-phase, mitotic cyclin (CM) is degraded, PO4 at activation site is removed and the cell enters into G, again.
===== Connecting With Me For More Knowledge Of Biology =====
Download My App just search - Gujarat Biology NEET PLUS on google play store
Link 👇
MANISH MEVADA
M.Sc, M.Phil, B.Ed
GUJARAT BIOLOGY NEET
NEET MATERIAL IN GUJARATI
KNOWLEDGE ON THE WAY....................
Please Do Not enter any sparm link in comment box