Cell Divison

Cell Biology Cell Division Unit

What is cell division?

Cell division is the fundamental process by which a parent cell divides into two or more daughter cells, essential for growth, repair, and reproduction in all living organisms.

What is the purpose of cell division in multicellular organisms?

In multicellular organisms, cell division serves several vital purposes: for growth (increasing the number of cells), for repair (replacing damaged tissues), and for renewal (constantly replacing dead or worn-out cells to maintain tissue health).

What is the purpose of cell division in unicellular organisms?

For unicellular organisms, cell division is primarily the means of reproduction, producing entirely new, genetically identical organisms (often through asexual reproduction).

What is cancer in the context of cell division?

Cancer is a serious disease characterized by uncontrolled cell division, where cells bypass the normal regulatory checkpoints of the cell cycle, leading to rapid proliferation and often forming malignant tumors that can invade other tissues.

Define the Cell Cycle.

The cell cycle is the ordered and highly regulated sequence of events that a cell undergoes from its formation until it divides into two new daughter cells. It encompasses phases of growth, DNA replication, and subsequent division.

What are the two main phases of the cell cycle?

The two main phases of the cell cycle are:

• Interphase: A period of cell growth, DNA replication, and preparation for division.

• M phase (Mitotic phase): The period of actual cell division, comprising mitosis and cytokinesis.

What happens during Interphase?

During Interphase, the cell undergoes significant growth, duplicates its DNA, and synthesizes proteins and organelles in preparation for cell division. This phase accounts for approximately 90\% of the entire cell cycle.

Name the three sub-phases of Interphase.

The three distinct sub-phases of Interphase are: G1 phase (Gap 1), S phase (Synthesis), and G2 phase (Gap 2).

What occurs during the G_1 phase?

During the G_1 phase, the cell grows significantly in size, synthesizes proteins and organelles, and performs its normal metabolic functions. It acts as a primary growth stage before DNA replication.

What is the key event during the S phase?

The key event during the S phase is DNA replication, where the cell's entire genetic material is accurately duplicated. This results in each chromosome consisting of two identical sister chromatids.

What is the cell preparing for during the G_2 phase?

During the G_2 phase, the cell continues to grow, synthesizes proteins (such as those needed for spindle formation), and actively checks for any DNA damage or replication errors before entering mitosis. It is a critical checkpoint for genomic integrity.

What does the M phase include?

The M phase (Mitotic phase) includes two major processes:

• Mitosis: The division of the nucleus and its duplicated chromosomes.

• Cytokinesis: The subsequent division of the cytoplasm and organelles, leading to the formation of two separate daughter cells.

Differentiate between Mitosis and Cytokinesis.

• Mitosis: This is the process of nuclear division, ensuring that each of the two resulting nuclei receives an identical set of chromosomes.

• Cytokinesis: This is the division of the cell's cytoplasm and its organelles, following mitosis, to physically separate the two daughter cells.

What is the primary outcome of mitosis?

The primary outcome of mitosis is the faithful division of the nucleus of a somatic (body) cell into two genetically identical nuclei, each containing the same number and type of chromosomes as the original parent cell. This process ensures the creation of two identical daughter cells.

List the stages of mitosis.

The four main stages of mitosis are: Prophase, Metaphase, Anaphase, and Telophase.

What happens during Prophase?

During Prophase, the duplicated chromosomes condense and become visible under a microscope. The nuclear envelope begins to break down, and the mitotic spindle starts to form from the centrosomes.

Describe Metaphase.

In Metaphase, the highly condensed chromosomes align precisely along the cell’s equatorial plane, known as the metaphase plate. Each sister chromatid is firmly attached to a spindle fiber from opposite poles of the cell.

What is the key event of Anaphase?

The key event of Anaphase is the crucial separation of sister chromatids. Specialized proteins (cohesins) holding them together are cleaved, allowing individual chromatids (now considered full chromosomes) to be pulled by the spindle fibers towards opposite poles of the cell.

What forms during Telophase?

During Telophase, two new nuclear envelopes begin to reform around the separated sets of chromosomes at each pole of the cell. The chromosomes decondense, and the mitotic spindle disassembles. Cytokinesis usually begins during this stage.

What is a Genome?

A Genome refers to the complete set of genetic material (DNA, and sometimes RNA in certain viruses) present in an organism or cell. It contains all the instructions needed for an organism to develop and function.

What is a DNA molecule?

A DNA molecule is a long, highly complex, double-stranded helical structure composed of nucleotides, carrying the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses.

Define Chromatin.

Chromatin is the complex material found within the nucleus of eukaryotic cells, consisting of DNA tightly coiled around proteins called histones. In this uncondensed state (often described as