What is Cell Cycle?
The succession of occasions by which a cell copies its genome and synthesises any remaining cell contents and then ultimately separates into two daughter cells is known as cell cycle. The cell cycle is a four-stage process in which the cell increases in size (gap 1, or G1, stage), duplicates its DNA (synthesis, or S, stage), prepares for division (gap 2, or G2, stage), and divides (mitosis, or M, stage).
The cell cycle is partitioned into two stages called (I) Interphase: the period of preparation for cell division, and (ii) Mitosis (M stage): the real-time cell division. Interphase is additionally partitioned into G1, S, and G2. The G1 stage is the period when the cell develops and completes normal metabolism.
Growth is proportional to reproduction in unicellular organisms (such as Amoeba, Euglena, and Paramecium). While in multicellular organisms, growth and reproduction are different phenomena.
Phases of Cell Cycle
(A) Interphase
Interphase cell cycle is further divided into different phases.
(B) M Phase: Here, actual cell division happens. The number of chromosomes in the parent and daughter cells remains the same, so it is called equational division.
(C) Karyokinesis: The nuclear division is trailed by cytokinesis, for example, the division of the cytoplasm to bring about two daughter cells.
Phases of cell cycle
Cell Division
Cell division happens when cells multiply involving both nuclear and cytoplasmic divisions.
There are two sorts of cell division: mitosis and meiosis.
More often than not when individuals refer to "cell division," they mean mitosis, the most common way of making new body cells.
Meiosis is the kind of cell division that makes egg and sperm cells. Mitosis is a fundamental process.
Mitosis
Different stages of mitosis
Mitosis forms the somatic cells of the body.
All cells of the body except germ cells go under mitosis.
Flemming (1882) was the one who coined this term.
It is popularly known as equational division because chromosomes replicate and get equally distributed quantitatively as well as qualitatively into two daughter nuclei.
Depending upon the type of cell and species, it can vary from 30 minutes to 3 hours for completion.
It consists of two major steps: Karyokinesis and Cytokinesis.
Meiosis
Meiosis is a kind of cell division that reduces the number of chromosomes in the parent cell significantly and produces four gamete cells.
This interaction is expected to deliver egg and sperm cells for sexual reproduction.
The consequence of meiosis is the development of four unique cells, each conveying another combination of genes and chromosomes, and each with a half of the quantity of original chromosomes, subsequently maintaining the chromosome number of an animal variety from one generation to another.
The significant periods of meiosis include Interphase, prophase I, metaphase I, anaphase I, telophase I, cytokinesis, interphase II, metaphase II, anaphase II, and telophase II.
Cell Division Phases
Prophase
Prophase of mitosis
It is the first and the longest phase of mitotic cell division.
Chromosomes become visible as short and thick.
Each chromosome splits into two chromatids connected at the centromere.
The nuclear membrane and nucleolus start dissolving.
Chromosomes become shorter and thicker.
Metaphase
Nuclear membrane and nucleolus disintegrate and disappear completely.
Spindle fibres start appearing and these fibres get attached to chromosomes at centromeres.
Chromosomes become shorter and thicker.
Chromosomes arrange themselves in the centre or on the equatorial plate.
At the end of metaphase, the two chromatids of each chromosome also start separating.
Anaphase
Chromatids separate from each other at the centromere and are called daughter chromosomes.
These daughter chromosomes move to the opposite poles forming “U” or “J” shapes during their movement towards the pole.
Telophase
Telophase of mitosis
Daughter chromosomes are now at the end of the spindle, i.e., present at the opposite poles.
Reformation of the nuclear membrane around each daughter chromosome.
Nucleolus reforms.
Two nuclei are thus organised singly at each pole of the parent cell.
Chromosomes begin to lose their compact structure.
Spindle fibres disappear gradually.
Cytokinesis
In animal cells, a ring of actin filaments forms at the metaphase plate.
The ring contracts, forming a cleavage furrow, which further divides the cell in two.
In plant cells, Golgi vesicles coalesce at the metaphase plate, forming a phragmoplast.
A cell plate formed by the fusion of the vesicles of the phragmoplast grows from a centre toward the cell walls and the membranes of the vesicles fuse to form a plasma membrane which divides the cell in two.
Correct Sequence of Cell Cycle
The correct sequence of cell cycle stages in the cell is G1 → S → G2 → M.
On the other hand, meiosis includes interphase, prophase I, metaphase I, anaphase I, telophase I, cytokinesis, interphase II, metaphase II, anaphase II, and telophase II.
Significance of Mitosis
It results in the formation of two daughter cells identical to the parents.
DNA is distributed equally due to this process in both the daughter nuclei.
Both daughter cells are identical and have the same genetic constitution.
The number of chromosomes remains the same from one generation to the other.
It is used for growth and repair.
Cells are diploid.
It is the only way to increase the cell number without changing the genetic material.
Mitosis always maintains the gap between two rounds of cell division which is essential for:
Repair of DNA damages
And cytoplasmic growth of the cell.
Conclusion
This article has given all the necessary detail about the Phases of the cell cycle with respect to the NEET syllabus. The questions added at the end of the article are frequently asked questions and are important from the exam point of view and thus the student can have a clear understanding of the type of questions that might come in the exam.
FAQs on Phases of Cell Cycle - Important Topic for NEET
1. How many questions can you expect from the cell cycle in the NEET examination?
This topic holds a strong weightage in the examination and on average 6 questions are asked from this unit. Almost every year, you can expect one question from this topic. It has around 10% weightage in the examination.
A student must thoroughly go through each line and diagram of the NCERT and make tables to revise these topics in the long run separately. Students can also get innovative with diagrams and can form sticky notes, mind maps, and mnemonics for better understanding and easy recalling during the examination.
2. What are the most important topics to cover from this part of the unit?
Though this complete topic is very important from an exam point of view, you surely can’t afford to miss the differences and characteristics between phases like prophase, metaphase, anaphase, and telophase.
The student should thoroughly read and practise NCERT with some additional information to sail through this examination. You must pay attention to every detail and diagram given in the book, you must practise and revise the concepts at a regular interval of time so that they will become easier to recall in the examination.