Describe the function of DNA polymerase

3.3.7 · Biology › DNA Structure & Replication

DNA polymerase KYA hai?

Yaad rakhne wale key facts:

Yeh sirf 5′ → 3′ direction mein kaam karta hai (yeh nayi nucleotides 3′-OH end par add karta hai).
Yeh kuch nahi se shuru nahi kar sakta — isse ek pehle se maujood primer chahiye hota hai jisme free 3′-OH ho taaki extend kar sake.
Iske paas proofreading ki ability hai (3′→5′ exonuclease) jo galat-pair hui bases ko remove karti hai.

Yeh aise hi kyun kaam karta hai? (first principles)

Yeh strand KAISE banata hai (mechanism, derived)

Socho template strand $3' \to 5'$ direction mein chal rahi hai. Nayi strand antiparallel honi chahiye, isliye yeh $5' \to 3'$ grow karti hai.

Step by step (har step ka ek Kyun? hai):

Template base padho. Kyun? Agla base complementary hona chahiye, isliye enzyme ko dekhna padta hai ki woh kis cheez ke against pair kar raha hai.
Matching dNTP select karo. Ek free triphosphate nucleotide float hokar aata hai aur apna fit test karta hai (A↔T, G↔C). Kyun? Sirf sahi pair stable hydrogen bonds banata hai aur enzyme ki shape mein fit hota hai — isi tarah accuracy enforce hoti hai.
Bond banao. Growing chain ka 3′-OH incoming dNTP ke innermost phosphate par attack karta hai. Ek phosphodiester bond banta hai aur pyrophosphate (PPᵢ) release hota hai. Kyun? High-energy triphosphate ko todne se woh energy milti hai jo bond banane ke liye chahiye — alag ATP ki zaroorat nahi.
Proofread karo. Agar galat base add ho gaya, toh polymerase ki 3′→5′ exonuclease use kaat deti hai aur dobara try karti hai. Kyun? Yeh error rate ko dramatically kam karta hai (≈1 in 10⁹ bases), genetic information ko accurate rakhte hue.
Repeat karo, template ke saath aage badhte hue.

Figure — Describe the function of DNA polymerase

Leading vs lagging strand (5′→3′ only ka ek consequence)

Common Mistakes (Steel-manned)

Recall Feynman: 12-saal ke bachche ko samjhao

DNA polymerase ek bahut careful typist ki tarah hai jo ek zipper ki aadhi side copy kar raha hai. Woh purani aadhi ke har daant ko dekhta hai aur nayi aadhi banane ke liye matching daant snap karta hai. Woh daant sirf ek end par add kar sakta hai (kabhi shuru se nahi), isliye ek chhota helper pehla daant uske liye lagata hai. Aur woh itna careful hai ki har daant check karta hai aur jo fit nahi hote unhe nikalke phenk deta hai. Aise hi tumhare cells vibhajit hone se pehle apne saare DNA ki near-perfect copies banate hain.

Active Recall Flashcards

DNA polymerase ka kya function hai?

Yeh template strand use karke growing chain ke 3′ end par complementary nucleotides add karke ek nayi DNA strand synthesise karta hai.

DNA polymerase nayi strand kis direction mein synthesise karta hai?

5′ → 3′ (template ko 3′ → 5′ padhte hue).

DNA polymerase sirf 3′ end par hi kyun add karta hai?

Nayi nucleotides triphosphates ke roop mein aati hain; bonding ke liye free 3′-OH ka react karna zaroori hai, isliye growth 5′→3′ hoti hai.

DNA polymerase shuru karne se pehle kya maujood hona chahiye?

Ek free 3′-OH wala primer (primase se bana RNA primer).

Nucleotides join karne ki energy kahaan se aati hai?

Incoming nucleoside triphosphate (dNTP) se jab pyrophosphate (PPᵢ) release hota hai — alag ATP se nahi.

Proofreading kya hai aur kaunsi activity yeh kaam karti hai?

3′→5′ exonuclease activity dwara mismatched bases ko remove karna, high accuracy ensure karte hue.

DNA unwind kaun karta hai (polymerase nahi)?

Helicase.

Okazaki fragments kya hain?

Lagging strand par discontinuously bane chhote DNA segments, jo baad mein DNA ligase dwara jode jaate hain.

Template 3′–GCTA–5′ hai; kaunsi nayi strand banti hai (5′→3′)?

5′–CGAT–3′.

Okazaki fragments ko kaun jodta hai?

DNA ligase.

Connections

DNA Structure — antiparallel strands 5′→3′ rule explain karte hain.
Complementary Base Pairing — woh rule jo polymerase enforce karta hai.
Helicase — polymerase se aage DNA unwind karta hai.
Primase and RNA Primers — starting 3′-OH provide karte hain.
DNA Ligase — nicks seal karta hai aur Okazaki fragments jodta hai.
Semiconservative Replication — overall process jise polymerase serve karta hai.
Leading and Lagging Strands — polymerase ki one-way action ka direct consequence.