Archana

1. Cell Cycle Overview:

The cell cycle is the process by which a cell grows, prepares for division, and then divides to form two daughter cells.

Main Phases:

Interphase (the cell prepares for division)

M phase (Mitotic phase) (the cell divides

Interphase (Preparation for cell division):

Interphase takes up most of the cell cycle time and is divided into three stages:

a. G₁ phase (Gap 1):

The cell grows in size.

It produces RNA, proteins, and organelles.

It performs normal cell functions.

This is a checkpoint to decide if the cell should divide.

b. S phase (Synthesis):

DNA is replicated (copied) so each daughter cell will get a complete set.

Chromosomes become duplicated but still joined (as sister chromatids).

c. G₂ phase (Gap 2):

The cell continues to grow.

It makes final preparations for division (e.g., more proteins, organelles).

Another checkpoint ensures DNA is copied correctly.

M Phase (Mitotic Phase):

This is when the cell actually divides. It has two main parts:

Mitosis (division of the nucleus)

Cytokinesis (division of the cytoplasm)

Mitosis is divided into 4 stages:

1. Prophase:

Chromatin condenses into visible chromosomes.

Each chromosome has two sister chromatids.

The nuclear envelope breaks down.

Spindle fibers begin to form.

2. Metaphase:

Chromosomes line up at the middle of the cell (equator).

Spindle fibers attach to the centromeres of the chromosomes.

3. Anaphase:

Sister chromatids are pulled apart to opposite poles by the spindle fibers.

Each chromatid becomes an individual chromosome.

4. Telophase:

Chromosomes begin to uncoil back into chromatin.

Two new nuclear envelopes form around the chromosomes.

The cell starts to pinch in the middle (cleavage).

Cytokinesis:

The cytoplasm divides.

Two identical da

ughter cells are formed.