5.7.4 · HinglishMicrobiology
Explain bacterial genetic exchange (conjugation, transformation, transduction)
5.7.4· Biology › Microbiology
KYA ho raha hai (badi picture)
Teeno differ karte hain DNA kaise travel karta hai isse:
| Mechanism | DNA carrier | Cell contact zaroori hai? | DNA source |
|---|---|---|---|
| Conjugation | pilus/bridge se plasmid | Haan (direct) | living donor cell |
| Transformation | environment se free naked DNA | Nahi | dead/lysed cell |
| Transduction | bacteriophage (virus) | Nahi | pichla host bacterium |
1. Conjugation — plasmid handshake
YEH KYU kaam karta hai — step by step derive karo:
- F⁺ (donor) cell F plasmid carry karta hai, jisme genes (tra genes) hote hain ek sex pilus banane ke liye.
- KAISE: F⁺ ka pilus F⁻ (recipient) se contact karta hai, phir retract karta hai, dono cells ko saath kheenchta hai → ek conjugation bridge (mating channel) banta hai.
- F plasmid ka ek strand oriT site par nick hota hai aur ek single strand ke roop mein recipient mein transfer hota hai.
- Dono cells complementary strand synthesise karti hain (rolling-circle replication) → ab dono cells F⁺ hain.
Hfr cells (kyun chromosomal genes transfer ho sakte hain): Agar F plasmid bacterial chromosome mein integrate ho jaaye, toh cell Hfr (High frequency recombination) ban jaati hai. Ab transfer chromosome ko bhi saath kheechnaa shuru karta hai. Transfer usually poora chromosome move hone se pehle interrupt ho jaata hai, isliye oriT ke paas wale genes pehle transfer hote hain — isi tarah scientists gene order map karte hain (interrupted mating experiment: time = distance).
2. Transformation — naked DNA uthana
KAISE / KYU:
- Ek bacterium competent hona chahiye — uske surface proteins hone chahiye jo DNA bind aur import karte hain. Competence aksar stress/high cell density se trigger hoti hai.
- Naked DNA fragment bind karta hai → ek strand degrade hota hai, doosra andar jaata hai.
- Incoming strand chromosome ke ek homologous region ke saath pair karta hai aur homologous recombination se insert hota hai.
3. Transduction — virus courier
Do types — KYU do? kyunki yeh depend karta hai ki phage DNA kaise package karta hai:
(a) Generalised transduction (lytic cycle error):
- Phage infect karta hai, host DNA ko chop karta hai, aur replicate karta hai.
- Transfer KAISE hota hai: packaging ke dauran phage accidentally phage DNA ki jagah bacterial DNA ka ek tukda phage head mein bharta hai.
- Yeh defective phage bacterial DNA ek nayi cell mein inject karta hai → recombination. Koi bhi gene move ho sakta hai (isliye "generalised").
(b) Specialised transduction (lysogenic cycle):
- Ek temperate phage chromosome mein ek specific site par prophage ke roop mein integrate ho jaata hai.
- Excision par kabhi kabhi adjacent host genes bhi saath le jaata hai.
- Sirf integration site ke paas wale genes transfer hote hain (isliye "specialised").
Apni galtiyon ko Steel-man karo
Active recall
Recall Quick self-test (answers cover karo!)
- Kaun sa mechanism direct cell-to-cell contact chahta hai? → Conjugation
- Kaun se ko virus chahiye? → Transduction
- Kaun sa environment se free DNA use karta hai? → Transformation
- F⁻ ko F⁺ mein kya convert karta hai? → conjugation se F plasmid ka transfer.
- Hfr cell kya hai? → cell jisme F plasmid chromosome mein integrated hai.
- Transformation kis experiment ne prove kiya? → Griffith's (1928).
Recall Feynman: ek 12-saal ke bacche ko explain karo
Bacteria fancy tarike se bachhe nahi kar sakte, isliye woh zinda rehte hue gene "trading cards" swap karte hain.
- Conjugation: do bacteria ek choti tube se haath milaate hain aur ek ek card cross bhejta hai.
- Transformation: ek bacterium zameen par pada card dhundhta hai (ek mare hue ne gira diya tha) aur use uthata hai.
- Transduction: ek virus ek mail truck ki tarah hai jo accidentally pichle ghar ka card agले ghar mein deliver kar deta hai. Teeno bacteria ko nayi powers (jaise medicine ko resist karna) bahut tez dete hain.
Flashcards
Horizontal gene transfer kya hai?
DNA ka organisms ke beech movement jo parent-to-offspring (vertical) inheritance ke alaawa hota hai.
Bacterial genetic exchange ke teen mechanisms ke naam batao.
Conjugation, transformation, transduction.
Kaun sa mechanism pilus ke zariye direct cell-to-cell contact chahta hai?
Conjugation.
Conjugation bridge kaun si structure banati hai?
Sex (F) pilus, jo F plasmid par tra genes se encoded hai.
Conjugation ke dauran kitne DNA strands transfer hote hain, aur kyun?
Ek (single) strand; donor apni copy rakhta hai aur dono cells complement resynthesize karti hain (rolling-circle).
F⁺ cell aur F⁻ cell mein kya fark hai?
F⁺ F plasmid carry karta hai (donor); F⁻ mein yeh nahi hota (recipient).
Hfr cell kya hai?
Ek cell jisme F plasmid chromosome mein integrate ho gaya hai → chromosomal genes high frequency par transfer karta hai.
Genetics mein Hfr cells kyun useful hain?
Interrupted-mating gene order dikhata hai (transfer time ∝ map distance).
Transformation define karo.
Environment se free naked DNA ka uptake aur genome mein uski recombination.
Competent cell kya hai?
Ek cell jo external DNA bind aur le sakti hai.
Transformation kis experiment ne demonstrate kiya?
Griffith ka 1928 pneumococcus experiment.
"Transforming principle" (Avery et al.) kya hai?
DNA.
Transduction define karo.
Bacterial DNA ka ek cell se doosri cell mein bacteriophage ke zariye transfer.
Generalised transduction kaun se phage cycle ke dauran hota hai?
Lytic cycle (host DNA ki random mis-packaging).
Specialised transduction kaun se phage cycle ke dauran hota hai?
Lysogenic cycle (faulty prophage excision adjacent genes le jaati hai).
Kaun sa transduction type koi bhi gene transfer kar sakta hai?
Generalised transduction.
Kaun sa transduction type sirf prophage site ke paas wale genes transfer karta hai?
Specialised transduction.
Conjugation clinically kyun important hai?
R-plasmids antibiotic resistance rapidly spread karte hain, species ke beech bhi.
Connections
- Plasmids and F factor
- Bacteriophage lytic and lysogenic cycles
- Homologous recombination
- Antibiotic resistance mechanisms
- Griffith and Avery experiments
- Binary fission (vertical transfer)
- DNA as genetic material