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Cell Cycle and Cell Division | NCERT Lines + PYQ's Solving | NEET 2024 Biology | Basavaraj Sir

Vedantu NEET English・2 minutes read

Basaj introduces cell cycle and division in virtual class, detailing phases like mitosis and meiosis with their significance. Cell cycle involves growth, DNA replication, and division with detailed processes like G1, S, and G2 phases, leading to mitosis or meiosis.

Insights

The cell cycle involves cell growth, DNA replication, and cell division, with DNA concentration increasing from 2C to 4C.
Human cells take approximately 24 hours to complete their cell cycle, spending most of the time in the interface phase.
Mitosis is crucial for maintaining the balance between DNA content and cytoplasmic content, ensuring a 2N and 2C state in cells.
Meiosis reduces the chromosome number by half during gamete formation, leading to four haploid cells at the end of meiosis 2.

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What is the cell cycle?
The cell cycle is a sequence of events where a cell duplicates its genome, increases in size, synthesizes other cell constituents, and divides into two daughter cells.

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Summary

00:00

"Cell Cycle: Biology Master's Virtual Class"

Basaj, the biology Master teacher, introduces the topic of the cell cycle and cell division to students in a virtual class.
The first cell in the human body is the zygote, which is deployed in nature.
The process of cell division allows a single cell to develop into a multicellular organism.
The cell cycle chapter covers phases such as cell cycle, mitosis, and meiosis, each with its significance.
The cell cycle involves cell growth, DNA replication, and cell division, with DNA concentration increasing from 2C to 4C.
Cell cycle is defined as a sequence of events where a cell duplicates its genome, increases in size, synthesizes other cell constituents, and divides into two daughter cells.
Cell division is genetically controlled and not under individual control.
Bacteria have a cell division rate of 18 to 20 minutes, while yeast completes its cell cycle in around 90 minutes.
Human cells take approximately 24 hours to complete their cell cycle.
The cell cycle is divided into two phases: interphase and the Y phase, which represents mitosis or meiosis.

16:44

Cell Cycle: Interface and Yum Phase

In a movie scenario, a 3-hour movie consists of 1.5 hours of movie followed by a 10-minute break and another 1.5 hours of movie.
In the cell cycle, the opposite occurs with 1.5 hours of break time called the interface, followed by a 10-minute phase called the Yum face, and then another 1.5 hours of interface.
Within a human cell's 24-hour cycle, 95% of the time is spent in the interface, where the cell is resting, while the remaining 5% is spent in the Yum phase.
During the 24-hour cycle, a cell spends approximately 23 hours in the interface and 1 hour in the Yum phase, preparing for cell division.
The interface is a period of preparation for the Yum phase, similar to how moviegoers use intermissions to buy popcorn or go to the washroom.
In the interface, the cell is metabolically active, producing and synthesizing biomolecules, preparing for cell division.
The G1 phase, also known as the post-mitotic phase, is the longest phase of the cell cycle, characterized by an increase in cell size and production of nucleotides, RNA, and proteins, but no DNA replication.
Some cells exit the cell cycle after the G1 phase, entering a quiescent stage known as the G0 phase, where they become inactive and do not proliferate.
The S phase involves the replication of DNA molecules on each chromosome, leading to an increase in DNA content but not in the number of chromosomes, retaining the original ploidy.
Genes are duplicated during the S phase, emphasizing the importance of DNA replication in cell division.

35:14

Cell Cycle: DNA Duplication and Mitosis Phases

DNA duplication occurs in the S phase, increasing DNA content from 2C to 4C.
The S phase, or synthesis phase, involves DNA replication but not an increase in the number of chromosomes.
The G2 phase sees the duplication of mitochondria and chloroplasts, along with spindle fiber formation.
Functions of the S phase include DNA replication, centriole formation, and histone protein synthesis.
The G2 phase involves the duplication of mitochondria and chloroplasts, spindle protein formation, and RNA and protein synthesis.
The cell cycle is regulated by cyclin-dependent kinase (CDK) proteins, ensuring proper cell cycle progression.
Mitosis restores the balance between DNA content and cytoplasmic content, maintaining a 2N and 2C state.
Mitotic cell division is common in diploid somatic cells, with exceptions like male honeybees and certain plant species like algae.
Mitosis involves stages like prophase, metaphase, anaphase, and telophase, starting with chromatin condensation in prophase.
Prophase also sees the radiating out of microtubules called asters from centrosomes, aiding in chromosome organization.

53:55

Mitosis: Cell Division and Chromosome Movement

Asters are attached to the plasma membrane, along with spindle fibers released from the centrosome, forming the mitotic apparatus.
Prophase involves the condensation of chromatin to form chromosomes, the formation of Asters and spindle fibers, and the disappearance of the nuclear envelope, Golgi body, and endoplasmic reticulum.
Metaphase includes the disintegration of the nuclear envelope, complete chromosome condensation, and the alignment of chromosomes at the equator to form the metaphase plate.
Anaphase sees the separation of sister chromatids, resulting in a 4N and 4C chromosome content, with chromatids migrating towards opposite poles.
Telophase involves the clustering of chromosomes at the poles, decondensation of chromosomes, and the reformation of the nuclear envelope, Golgi body, endoplasmic reticulum, leading to the formation of two cells with 2N and 2C content.
Cytokinesis in animal cells involves the formation of a cleavage furrow that pinches the cell into two, while in plant cells, a cell plate made of fragmoplast divides the cell from the center outwards.
Mitosis is significant for growth, development, repair, reproduction in unicellular organisms, continuous growth in meristems, and restoring the nucleocytoplasmic ratio by maintaining the balance between nuclear and cytoplasmic content.
The significance of metaphase lies in its role in growth, development, repair, reproduction in unicellular organisms, continuous growth in meristems, and restoring the nucleocytoplasmic ratio by maintaining the balance between nuclear and cytoplasmic content.

01:12:12

Cell Division: Nucleus, DNA, and Chromosomes

Cyto kinesis in cell division involves the division of the nucleus but not the cell, leading to a multi-nucleated condition in the absence of cytokinesis.
The nucleocytoplasmic ratio in mitosis varies, with the DNA content doubling during the S phase, resulting in a 2 and 4 C ratio.
The weightage of the chapter on cyto kinesis, along with biomolecules and cell cycle, is approximately 11% in biology.
The G1 phase lacks cell division and DNA replication, while the S phase sees DNA replication, increasing the DNA content to 4 C.
The DNA content reverts to 2 C during prophase, metaphase, and anaphase, with the chromosome number doubling in the S phase due to DNA replication.
Chromosome number and ploidy differ, with humans having 23 pairs of chromosomes (46 total) and being 2N organisms.
Meiosis occurs in germ cells during gamete formation, reducing the chromosome number by half to 23 chromosomes.
Meiosis involves two cycles of nuclear and cell division, with meiosis 1 reducing ploidy and meiosis 2 maintaining ploidy.
Meiosis 1 starts after parental chromosomes replicate to form identical sister chromatids during the S phase.
Meiosis 1 is known as reduction division, while meiosis 2 is equational division, similar to mitosis, with DNA replication occurring only in the S phase of meiosis 1.

01:34:13

Chromosomes, Meiosis, and Cell Division Explained

Chromosomes have two centromeres, making them distinct.
Erasing a part of a chromosome results in two chromosomes.
DNA content in chromosomes cannot be differentiated visually.
Homologous chromosomes pair up during meiosis.
Crossing over occurs between non-sister chromatids of homologous chromosomes.
Meiosis results in four haploid cells at the end of meiosis 2.
Meiotic events are categorized into prophase, metaphase, anaphase, and telophase.
Prophase 1 is divided into leptotene, zygotene, pachytene, diplotene, and diakinesis.
Leptotene involves the condensation of chromatin to form chromosomes.
Zygotene includes the pairing of chromosomes through synapsis, forming a synaptonemal complex.

01:54:18

Key Events in Cell Division: Condensation to Cytokinesis

Chromosome condensation is crucial for mitotic spindle assembly after prophase, leading to metaphase where spindal fibers are ready.
Nucleolus disappears, and the nuclear envelope breaks down at the end of prophase, marking the transition to metaphase.
In metaphase 1 of meiosis, two equatorial plates form, and spindal fibers attach to homologous chromosomes at the Kore region.
Anaphase 1 of meiosis sees homologous chromosomes separating, not sister chromatids, unlike in mitosis.
Telophase 1 marks the reappearance of the nucleolus and nuclear membrane, followed by cytokinesis to form haploid cells.
Meiosis 1 is followed by an interphase, prophase 2, where sister chromatids separate, resembling normal mitosis.

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