Cell Cycle
The cell
cycle is a fundamental, most crucial and highly regulated process that governs
the life of a cell. It is a series of process in which a cell grows, increases
its cytoplasm, duplicates its genetic material and ultimately divide into two
daughter cells. It is a very crucial process as it maintains the continuity of
life from single celled bacteria to highly complex multicellular organisms like
humans. The cell cycle is a dynamic process consisting of distinct phases and
various checkpoints to regulate the cell cycle process.
These phases are typically divided into
interphase and mitosis, although some cells, like those in the reproductive
organs, undergo an additional phase called meiosis.
The longest
cell cycle phase, interphase, is further broken into the three stages G1 (Gap
1), S (Synthesis), and G2 (Gap 2). The cell gathers the required materials and
energy during G1 to get ready for DNA synthesis. The cell then enters the S
phase, where it replicates its DNA to provide each daughter cell an identical
collection of genetic information. The cell undergoes further processing in G2,
during which it synthesizes various proteins and organelles required for the
next phase ( M phase).
The cell
splits its cytoplasm and nucleus during mitosis to produce two daughter cells
that are genetically identical, which is the culmination of the cell cycle.
Prophase, Metaphase, Anaphase, and Telophase are the many substages of mitosis,
each of which is responsible for a particular aspect of the creation of two
separate nuclei and the segregation of chromosomes.
Critical checkpoints, control mechanisms, and regulatory proteins
tightly govern the cell cycle to prevent errors and ensure that each phase
occurs accurately and in the correct order. These checkpoints keep the check on
the integrity of DNA and also look for various proteins, growth factors and
organelles required in the next phase to be synthesized properly or not.
Phases of cell cycle
All living
things are guaranteed to continue existing thanks to this essential biological
cycle. Gap 1, Synthesis, Gap 2, and Mitosis are the four main phases of the
cell cycle, respectively. In addition, some cells enter the G0 resting phase
when they stop dividing either temporarily or permanently.
1)Phase G1 (Gap 1)
The cell
cycle gets started in the G1 phase. It reflects the cell's initial phase of
growth and comes after cell division (mitosis or meiosis).
The cell
creates the RNA, proteins, and different organelles required for cell division
and function during this stage.
At a
critical phase known as the G1 checkpoint, the cell also keeps an eye on its
surroundings and internal conditions. It will move on to the following stage if
the circumstances are good and the cell is healthy. However, if there are
problems, the cell may enter G0 or experience cell death (apoptosis).
2)Synthesis Phase (S)
The cell
concentrates on DNA replication during the S phase. The nucleus's chromosomes,
which contain all of the genetic material, are duplicated.
This stage
is strictly controlled to guarantee precise genetic information replication and
guard against mistakes and mutations.
Each
chromosome is made up of two sister chromatids that are joined at the
centromere after the S phase. These sister chromatids share the same genetic
makeup.
3)Phase G2 (Gap 2)
The G2
phase, which serves as a second period of growth and preparation for cell
division, follows DNA replication in the cell.
The cell
continues to make proteins during G2, particularly those required for mitosis.
Additionally, it confirms that DNA replication proceeded properly and checks
for DNA damage.
Another
critical time when the cell determines whether it is prepared for mitosis is
the G2 checkpoint. When everything is in place, the cell moves on to the
subsequent stage.
4)Mitosis
The crucial
cell cycle mechanism of mitosis allows eukaryotic cells to divide into two
daughter nuclei that are genetically identical. In growth, tissue healing, and
asexual reproduction, it is essential. Prophase, Metaphase, Anaphase, and
Telophase are the four distinct stages of mitosis, and each step has unique
events and activities.
A)Prophase
Chromatin, a
combination of DNA and proteins, condenses into observable structures termed
chromosomes during prophase. Two sister chromatids, which are identical DNA
copies, make up each chromosome.
The
formation of the spindle apparatus is made possible by the nuclear envelope
starting to break down. The sister chromatids will be separated by this
microtubule-based structure.
Centrosomes,
which are hubs for organising microtubules, go to the cell's polar opposites.
Spindle fibres are microtubules that extend from the centrosomes in the
direction of the chromosomes.
B)Metaphase
The condensed
chromosomes align at the metaphase plate, which is the cell's equatorial plane,
during metaphase.
Each
chromatid's centromere is touched by spindle fibres from opposing centrosomes.
This guarantees that during anaphase, each chromatid will be drawn to its
opposing pole.
C)Anaphase
Sister
chromatids separate during anaphase. At the centromere, enzymes dissociate the
protein connections holding the chromatids together.
Each
chromatid that has been divided is treated as a separate chromosome. The
chromosomes are drawn towards the polar opposites of the cell when the spindle
fibres shrink.
In order to
maintain genetic integrity, this guarantees that each daughter cell will
receive an identical set of chromosomes.
D)Telophase
Prophase is
followed by telophase. At the opposite poles of the cell, the split chromosomes
are located.
Each set of
chromosomes forms a fresh nuclear envelope, encasing them in separate nuclei.
As they move
into interphase, chromosomes start to decondense again and transform back into
chromatin.
Cytokinesis
The last
stage of cell division, cytokinesis, frequently occurs during telophase. In
order to form two daughter cells, the cytoplasm and organelles of the cell must
be divided.
Actin
filaments create a contractile ring just below the cell membrane in animal
cells. In Animals this stage is done via cell furrow method, where a furrow
starts forming at the periphery and converging towards the centre and
ultimately dividing the cell into two daughter cells.
In plant
cells, a structure known as the cell plate develops in the cell's centre and
with time it moves towards the periphery dividing the cell into two daughter
cell.
Phase G0 (Resting Phase)
Not all
cells cycle through the G1, S, G2, and M stages continually. A non-dividing
state known as G0 is reached by some cells, including nerve and muscle cells.
Although
cells do not prepare for division or duplicate their DNA in G0, they are
metabolically active.
When
necessary, prompted by either internal or external triggers, cells in G0 may
leave this phase and enter the cell cycle once more.
Conclusion
The cell
cycle is not only important for understanding the fundamental process of the
life cycle of a cell but is also significant in understanding various diseases
which occur due to malfunctioning in the cell cycle process such as cancer.
G1, S, G2, and M are the four main phases of
the cell cycle, which is a complicated and tightly controlled process. Each
step serves a particular purpose, and checkpoints make sure the cycle is
running precisely and safely.
Mitosis is a
process in which two daughter cells are produced both genetically identical to
each other and having same number of chromosomes as the parent cells. These
daughter cells have the potential to develop further, carry out their distinct
tasks, or, in the case of unicellular organisms, continue to carry out all the
tasks required for life.
Mitosis is a
highly regulated process that ensures accurate genetic material distribution
and maintains genetic stability within an organism with the help of various
checkpoints and regulatory points. Any mitotic mistakes or irregularities might
have detrimental effects, such as cancer or genetic diseases.
