During which three phases are individual chromosomes no longer Visible

During Which Three Phases Are Individual Chromosomes No Longer Visible?

We all know that cell division is a series of events where the components of the cell divide. It proceeds through a series of stages – cell growth, synthesis of DNA, and division of components, generating two identical cells.

In eukaryotic cells, the stages are divided into two main phases – interphase and mitotic phase.

Throughout this cycle, there are only three phases in which the individual chromosomes become invisible. These are interphase, telophase, and cytokinesis.

1. INTERPHASE

It is the major part of the cell cycle where most of the development occurs. It occurs in 3 different steps:

1. G₁phase – This is the first gap phase, also known as the growth phase. We cannot see the individual chromosomes at this stage, and the chromatin fibers remain diffused and unorganized. The cell collects chromosomal DNA and protein building blocks in this phase, and stores enough energy to replicate every chromosome in the nucleus.
2. S phase –This is the synthesis phase, where a copy of DNA is synthesized inside the nucleus. Due to DNA replication, two identical copies of each chromosome called sister chromatids are created. These two sister chromatids are conjoined at the centromere region of each chromosome. The mitotic spindle, which controls how the chromosomes move during mitosis, develops from the two centrosomes, which separates during the M phase.
3. G₂phase – The second gap phase, or the G2 phase, is a time of increased cell growth, protein and organelle production, and content reorganization in preparation for mitosis. The cell produces the proteins required for chromosomal manipulation and restores its energy reserves. At this phase some cell organelles are replicated and cytoskeleton split to form mitotic spindle fibres. During G2, more cell proliferation could occur. Finally, the preparation for the mitotic phase must be finished before starting the mitosis.
4. MITOSIS PHASE

During this phase, the chromosomes in the nucleus divide into two identical sets. The mitosis is further divided into 4 further phases –

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
5. Prophase

During prophase, small vesicles begin forming when the nuclear membrane ruptures. The endoplasmic reticulum and the Golgi apparatus break apart and scatter to the cell's edge. Centrosomes begin to move to the opposite poles as the nucleolus disappears. The microtubules that form the base of the mitotic spindle then push the centrosomes apart as the microtubule fibres increase. The sister chromatids coil more tightly and are more visible below a light microscope.

2. Metaphase

The metaphase plate is, generally known as the equatorial plane, is where all chromosomes are lined up at the equator between the cell's two poles. Sister chromatids remain attached as the chromosomes at this stage show most shrinkage.

3. Anaphase

At the equatorial plane, the centromere divides into sister chromosomes. The orientation of the centrosome, where each chromatid's microtubule is attached, is quickly drawn by each chromatid, which is now known as a chromosome. At the metaphase plate, where they overlap, the non-kinetochore microtubules slide against one another, giving the impression that the cell is longer.

4. Telophase

As the chromosomes reach their opposing poles, they start to decondense and become invisible. During this process, each daughter cell's cytoskeleton will be assembled from the chromomere separated from the mitotic spindles. Chromosomes develop nuclear envelopes around them.

1. CYTOKINESIS

The cytoplasmic components of the two daughter cells are physically divided to complete cytokinesis. In this stage, the individual DNA becomes invisible and forms a cluster of nuclei. Cytokinesis occurs to divide a cell in two halves and to provide one nucleus to each of the cell.

In order to divide the cell in half and make sure that each daughter cell has one nucleus, cytokinesis must be performed. Cytokinesis begins at the anaphase phase of nuclear division and lasts all the way through telophase. At the equator of the cell, the contractile ring contracts, squeezing the plasma membrane inward and creating a cleavage furrow. The contractile ring eventually contracts until a plasma membrane connects two distinct cells.

FAQs

1. What are the stages of cell division?

Ans: The four stages of cell division are – prophase, metaphase, telophase, and anaphase.

2. Which phase of the cell cycle is the most crucial?

Ans: Interphase is the most important phase of the cell cycle. The cell cycle's longest phase is this one. This stage involves the cell preparing for division. During this stage, the cell expands and divides.

3. How many years do cells live?

Ans: It completely depends on the cell type. Your small intestine's cells only survive for 2-4 days. Skin cells live for 10 to 30 days. Sperm cells live for two months. A red blood cell's lifespan is 70–140 days. Some brain and ocular cells, as well as egg cells, are immortal.

4. What cell phase is the longest?

Ans: Interphase, the longest cell phase, is when the cell prepares for cell division and goes through normal growth activities.

5. How long does the cell cycle take?

Ans: The length of these cell cycle phases varies greatly in various types of cells. The G1 phase may last around 11 hours, the S phase around 8 hours, the G2 phase around 4 hours, and the M phase around 1 hour for a typical rapidly growing human cell with a total cycle period of 24 hours.