A E P Study Circle

The cell cycle is the series of events that a cell goes through to grow and divide. It has two main phases:

1. Interphase – The preparatory phase (about 90% of the cycle)
2. M Phase (Mitotic Phase) – The division phase

Interphase: The Growth & Preparation Stage

Interphase is divided into three sub-phases:

1. G₁ Phase (Gap 1)

• The cell grows in size.
• Organelles are duplicated.
• Proteins and enzymes necessary for DNA replication are synthesized.
• The cell performs its normal metabolic functions

2. S Phase (Synthesis)

• DNA replication occurs—each chromosome duplicates to form sister chromatids.
• The amount of DNA doubles, but the chromosome number remains the same.
• Centrosome duplication also begins.

3. G₂ Phase (Gap 2)

• Final growth before division.
• Synthesis of proteins required for mitosis (like spindle fibers).
• DNA is checked for errors and repaired if needed.

M Phase: The Division Stage (Mitosis)

Mitosis ensures the equal distribution of genetic material into two daughter cells. It has four key stages:

1. Prophase

• Chromatin condenses into visible chromosomes.
• Each chromosome has two sister chromatids joined at the centromere.
• The nuclear envelope breaks down.
• Spindle fibers begin to form from centrioles.

2. Metaphase

• Chromosomes align at the metaphase plate (cell equator).
• Spindle fibers attach to the centromeres via kinetochores.
• This is the most visually distinct phase under a microscope.

3. Anaphase

• Sister chromatids are pulled apart toward opposite poles.
• Once separated, each chromatid is considered an individual chromosome.
• This ensures equal genetic material in both daughter cells.

4. Telophase

• Chromosomes decondense back into chromatin.
• Nuclear envelopes re-form around each set of chromosomes.
• Spindle fibers disassemble.
• Followed by cytokinesis—division of the cytoplasm.

🧠 Quick Mnemonic for Mitosis Phases:

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(Prophase → Metaphase → Anaphase → Telophase)

The valency of carbon is 4, meaning it can form four covalent bonds with other atoms. This tetravalency allows carbon to bond with a variety of elements, including hydrogen, oxygen, nitrogen, and other carbon atoms.

The property that enables carbon to form long-chain compounds is called catenation. Catenation is the ability of carbon atoms to bond with other carbon atoms, forming straight chains, branched chains, or rings. This unique characteristic, combined with carbon’s small atomic size and strong covalent bonds, makes it the backbone of organic chemistry, leading to the vast diversity of organic compounds.