YEH KYUN ZAROORI HAI: Ek fertilized egg ~200 cell types ban jaata hai. Regulation ke bina, har cell har protein banayegi—complete chaos. Regulation spatial patterns (head vs. tail) aur temporal sequences (heart, fingers se pehle banta hai) create karta hai.
YEH KYA HAIN: DNA/histones par chemical tags jo sequence nahi badlte lekin accessibility badal dete hain
Modification
Effect
Example
DNA methylation
Gene silencing (CpG islands)
X-chromosome inactivation
Histone acetylation
Open chromatin (active)
Acetyl groups DNA-histone bond ko weaken karte hain
Histone methylation
Activate YA repress kar sakta hai
H3K4me3 (active), H3K27me3 (Polycomb repression)
YEH INHERIT KAISE HOTA HAI: Jab cells divide hoti hain, DNMT1 (maintenance methyltransferase) methyl marks ko new strand par copy karta hai. Histone marks chaperone proteins ke through partially maintain hote hain.
YEH KYUN MATTERS: Cellular memory explain karta hai—ek baar jab cell neuron ban jaati hai, woh neuron hi rehti hai chahe kitni bhi divisions ho jaayein. Original TF signals chale gaye, lekin chromatin "yaad rakhta hai."
Concept: Morphogen molecules ek source se diffuse hote hain, concentration gradient create karte hain. Cells apni position "padhti" hain morphogen levels sense karke.
YEH STEP KYUN? Tumhe spatial information chahiye. Exponential decay ka matlab hai: source ke paas = high morphogen = ek fate; door = low morphogen = alag fate.
Socho tum aur tumhara dost twins ho jinke paas identical instruction manuals (DNA) hain. Lekin tum race car banane ka decide karte ho, aur tumhara dost helicopter banata hai. Kaise? Tum dono alag-alag pages skip karte ho!
Tumhari body ki cells aisi hi hain. Har cell ke paas poora manual hai, lekin:
Brain cells sirf "thinking proteins" chapter padhti hain
Muscle cells sirf "movement proteins" chapter padhti hain
Woh choose kaise karte hain? Teen tricks:
Master switches (transcription factors): Special proteins jo manual mein bookmarks lagate hain, "yeh chapter padho!" bolte hue. Agar tumhare paas "muscle bookmark" protein hai, tum muscle cell ban jaate ho.
Permanent highlighter (epigenetics): Ek baar jab tum muscle chapter padhna shuru karo, tum use ek special ink se highlight karte ho jo highlighted rehti hai jab tum manual apni daughter cells ke liye photocopy karo. Woh bhi same pages padheingi.
Location, location, location (morphogens): Tumhari arm ki cells zyada "arm chemical" sunghti hain tumhari leg ki cells ke mukable. Woh smell unhe batata hai kaun se chapters padhne hain. High arm-chemical = "finger instructions padho."
Cool part? Isi tarah ek cell (fertilized egg) 30 trillion cells ban jaati hai jo alag-alag kaam karti hain—sab same instruction manual se!
Transcription Factors and Gene Expression—molecular switches
Cell Differentiation and Stem Cells—cells kaise fates commit karti hain
Homeotic Genes and Body Patterning—Hox genes as master regulators
Signal Transduction Pathways—external signals TF activation kaise trigger karte hain
Epigenetics and Inheritance—DNA sequence se aage chromatin modifications
Cancer Biology—jab developmental programs inappropriately reactivate hote hain
Evolutionary Developmental Biology—gene regulation changes evolution kaise drive karte hain
#flashcards/biology
Development mein gene regulation ka core principle kya hai? :: Identical DNA wali cells alag-alag subsets of genes alag-alag times aur locations par express karke differentiate hoti hain, jo transcription factors, epigenetic marks, aur signaling molecules se control hota hai.
Transcription factors kya hain aur yeh kya karte hain?
Proteins jo regulatory DNA sequences (enhancers/promoters) se bind karke gene transcription activate ya repress karte hain, gene expression ka combinatorial control create karte hain.
Gene expression ka combinatorial control explain karo :: Kai transcription factors ko saath bind karna padta hai (jaise ek lock mein keys) gene activate hone ke liye; yeh sharp ON/OFF decisions create karta hai aur ek genome ko bahut saare cell types specify karne deta hai.
Gene regulation mein Hill equation kya describe karti hai?
Expression = [TF]^n / (K_d^n + [TF]^n) cooperative binding describe karta hai jahan n > 1 steep response curves create karta hai, chhote TF changes se sharp gene activation trigger hota hai.
DNA methylation aur histone acetylation mein kya fark hai?
DNA methylation (cytosines mein methyl groups add karna) genes ko silence karta hai; histone acetylation (histone tails mein acetyl groups add karna) chromatin kholta hai aur genes activate karta hai.
Epigenetic memory kaise kaam karta hai?
DNMT1 replication ke dauran naye DNA strands par DNA methylation patterns copy karta hai; histone marks chaperones ke through partially maintain hote hain, jisse daughter cells gene expression states "yaad" rakh sakti hain.
Morphogen kya hai?
Ek signaling molecule jo concentration gradient banata hai aur cells ko positional information deta hai, alag-alag concentrations alag-alag cell fates specify karti hain.
Steady-state morphogen gradient equation derive karo
dC/dt = D(d²C/dx²) - λC se shuru karke, steady state par dC/dt = 0, solve karne par C(x) = C_0 × exp(-x/√(D/λ)) milta hai, jahan √(D/λ) decay length hai.
French Flag model kya hai?
Ek model jahan alag-alag morphogen concentration thresholds alag-alag genes activate karte hain, continuous gradient se cells ke discrete regions create hote hain (jaise ek flag par coloured stripes).
MyoD kya hai aur ise master regulator kyun kehte hain?
Ek transcription factor jo hundreds of muscle-specific genes activate karke muscle differentiation program shuru karta hai; "master" isliye kehte hain kyunki yeh artificially express hone par doosre cell types ko bhi muscle mein convert kar sakta hai.
Hox genes body patterning kaise control karte hain?
Hox genes transcription factors hain jo anterior-posterior axis ke saath overlapping domains mein express hote hain; unka combinatorial expression segment identity specify karta hai (jaise thorax vs. abdomen).
Somite segmentation clock kya hai?
Ek genetic oscillator jahan Hes7 gene negative feedback create karta hai (khud ko repress karta hai), periodic gene expression ~90 minutes mein cause karta hai jo rhythmic somite formation drive karta hai.
Differentiated cells genes kyun nahi kho deti?
Saari cells complete genome rakhti hain; iPSC experiments yeh prove karte hain adult cells ko Oct4/Sox2/Klf4/c-Myc transcription factors use karke pluripotency mein reprogram karke.
Enhancers apne target genes se door kaise ho sakte hain?
DNA chromatin remodeling ke through 3D loops banata hai, protein complexes ke zariye distant enhancers (kabhi kabhi megabases door) ko promoters se physical contact mein laata hai.
Neural tube development mein Sonic Hedgehog (Shh) gradient ka kya role hai?
Shh notochord se secrete hokar ventral-to-dorsal gradient create karta hai; high concentrations floor plate specify karte hain, intermediate levels motor neurons specify karte hain, low levels dorsal interneurons specify karti hain.
Developmental gene regulation ko robust kya banata hai?
Multiple redundant mechanisms (feedback loops, multiple enhancers, epigenetic locks, signal integration) ensure karte hain ki development noise, temperature variation, aur genetic differences ke bawajood sahi ho.
Development mein temporal control kyun important hai?
Structures ko sequence mein banana padta hai (jaise heart circulatory system se pehle); yeh gene cascades, delayed response elements, aur gradual chromatin remodeling se achieve hota hai.
Cooperative binding kya hai aur yeh kyun important hai? :: Jab pehle transcription factor ka binding nearby sites par baad ke TF binding ko facilitate karta hai; sharp developmental boundaries ke liye zaroori ultrasensitive (steep) response curves create karta hai.