Explain the function of mitosis

2.8.6 · Biology › Cell Division

WHAT is the function of mitosis?

Functions (yaani mitosis ek organism ke liye jo kaam karta hai) yeh hain:

1. Growth — cells ki number badhana taaki organism bada ho.
2. Repair — damaged ya worn out cells ko replace karna (jaise cut heal karna).
3. Replacement / maintenance — short-lived cells ko continuously renew karna (skin, gut lining, blood).
4. Asexual reproduction — kuch organisms mein (jaise Hydra budding, plant runners), poore naye individuals banana.

WHY must the copies be identical?

Toh asli reason yeh hai: ek multicellular body tabhi kaam karti hai jab saari cells ek hi genome share karti hain. Mitosis woh mechanism hai jo is fidelity ki guarantee deta hai.

HOW does mitosis achieve identical daughters? (Derivation from first principles)

Hume memorise nahi karna — hum reason out kar sakte hain ki mitosis ko kya KARNA CHAHIYE.

Step 1 — Goal define karo. Start: 1 cell jisme chromosome number $2n$ (diploid) hai. Required end: 2 cells, dono bhi $2n$, dono identical.

Yeh step kyun? Start aur required end define karne se pata chalta hai ki cell ko exactly kya problem solve karni hai.

Step 2 — Conservation requirement. Har daughter ko poori copy milne ke liye, DNA pehle duplicate hona chahiye.

Agar ek cell mein $C$ molecules of DNA hain aur woh sirf split ho jaaye, toh har daughter ko $C/2$ milega → half instructions. Yeh acceptable nahi. Isliye:

$\text{DNA before split}=2C\Rightarrow \text{each daughter}=\frac{2C}{2}=C$

Yeh step kyun? Yeh simple conservation of material hai. Do cells ko full set dene ke liye, pehle ek double set build karni hogi. Yeh duplication S phase (DNA synthesis) mein hoti hai, interphase mein, mitosis se pehle.

Step 3 — Har duplicated chromosome = do identical sister chromatids. Replication ke baad, har chromosome do sister chromatids hota hai jo ek centromere pe joined hote hain.

$\text{1 chromosome}\stackrel{\text{S phase}}{\to }\text{2 identical sister chromatids}$

Yeh step kyun? "Identical" ki requirement yahaan poori hoti hai — copy template base-pairing se banti hai, isliye chromatids exact duplicates hote hain.

Step 4 — Equal segregation. Sister chromatids ko pull apart kiya jaata hai taaki har chromosome ka ek chromatid har pole par jaaye.

$\text{daughter chromosome number}=\frac{2\times (\text{sister chromatids per chromosome set})}{2\text{ poles}}=2n$

Yeh step kyun? Sisters ko split karna (different chromosomes ke pairs ko nahi) yahi key trick hai — yeh guarantee karta hai ki dono sides ko har gene ki ek copy milti hai, isliye identical.

Conclusion (the formula of mitosis):

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Connections

• Cell Division
• Stages of Mitosis (PMAT)
• Interphase and the Cell Cycle
• Meiosis vs Mitosis
• DNA Replication
• Chromosomes and Chromatids
• Cancer and Uncontrolled Cell Division
• Asexual Reproduction

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