分子生物学(英文版)

Ｃhａpteｒ３Ｎucleic Acid

1.Phｙsiｃal ａnd ｃｈemicａl stｒuctuｒｅ of DNA

●Doｕｂlｅ-stranded helｉx

●Majoｒｇｒoｏve aｎｄ minor groove

●Base pairｉng

●Ｔhｅｔwｏsｔrands ａｒe ａｎｔiparallel

● G+C ｃontｅｎt（ｐerｃent Ｇ＋C)

●Ｓatelｌite DNA

Saｔellitｅ DＮAｃonｓｉｓts of ｈigｈｌy repeｔitive DNＡ and is so caｌleｄ beｃauseｒｅｐe ｔｉtionｓ of a sｈｏrt DNＡｓｅquence teｎｄ toｐroduce ａ diffｅｒent freｑueｎcｙ of the nucl ｅotides aｄeｎiｎe， cｙtosiｎe,guａｎiｎe aｎd tｈymｉne, and ｔhus have a diffeｒｅntｄen ｓiｔy ｆｒom bulk DＮA - such that thｅｙｆorｍ a ｓｅｃond or 'ｓaｔelｌｉte＇banｄwheｎｇｅｎomic DNA is ｓeparatｅｄ on ａdensitｙ grａdient.

2. Aｌｔernａtｅ DＮA structｕrｅ

Two baｓｅs hａveｂeeｎ extｒuded ｆｒom baｓe stacking at ｔhe jｕｎctioｎ. Thｅ white line ｇoes fｒoｍphosｐhａｔe ｔo pｈosphａtｅ alｏng the chain. Ｏ is ｓhowｎred, N blue, P yellｏw ａnd C gｒｅｙ．

3. Cirｃuｌａｒａnd suｐerhelicａl ＤNＡ

ＤNA ｃan ａlｓo ｆｏrm a douｂlｅ-strandｅd，ｃovａlentｌy－ｃｌoｓed cｉrcｌｅ．Ｔhese ｃｉｒｃulaｒｍｏleculeｓ are often cｏiled intｏ a supｅｒhelｉx, the ｆｏrmaｔiｏn oｆwｈich is ｃatａlyzｅd by ｅnzyｍes calｌeｄｔoｐoisomerases.

4.Denaturａｔｉon of DNA

Denaｔuｒatioｎ： A tｒaｎsition frｏm thｅ natｉｖｅｔo thｅｄeｎatureｄstate

DNA deｎatｕrａtｉoｎ： aｌso callｅｄDＮA melｔing， is tｈe proｃess bｙ whicｈdoｕblｅ-str ａｎdeｄ DNＡ unwinｄs ａnd separaｔｅs into ｓｉｎgle-ｓtranｄed strandsｔhrｏugh thｅｂreakin ｇ of ｈｙｄrｏgｅｎ boｎding between the ｂases.

Hyperｃhromicitｙ／Hｙperｃhromiｃ eｆfect: the ｓtriking increａｓｅｉｎ aｂsorｂance of DNA (Ａ260) cａｕsed by ｔｈe ｄeｎaturatｉon ｏf ｔｈe doｕbｌｅ－sｔranｄed DNA ｍｏlecule

Ｍelting ｔｅｍpeｒature (Tm) ：ｔhｅｔempｅraturｅ at wｈiｃｈ haｌf ｏf thｅDNＡ strands are in tｈe douｂle－helicａｌ staｔe aｎd ｈalｆ arｅｄｅnatｕｒed． Thｅmelｔinｇｔemperature deｐｅnds ｏｎ boｔh theｌengthｏｆｔhe moｌｅcule, anｄ the speciｆｉc nucｌｅotide seqｕeｎce ｃompositｉon oｆｔhat moleｃule.

Factors Ａｆｆｅｃting Tm

●G－Ｃ coｎtent oｆsａmｐｌe

● reagenｔs thａt increase tｈe ｓolubility of the bases(anｙthing thaｔｄisrｕｐtｓ H-bonds or base sｔackｉng）

●Salt concｅｎtratiｏn

● pH

● Length

5. Rｅnaturaｔion

Strands cａnｂe iｎduｃｅd to renａtｕｒｅ (annｅal) ｕnderｐroper conｄitiｏｎｓ. Facｔors to ｃonsｉｄer:

●Tempｅrａturｅ

● Salt concentratｉon

●ＤNA concentrａtion

● Time

RｅpｅtｉtivｅSequenｃes

●Ｕnique: SｉngｌｅCｏpyＧeneｓ

● Sliｇhｔly repetｉtive (2-10cｏpies)

● Mｉddle reｐeｔitive(10- hunｄrｅds)

--Clｕstered

--Diｓperｓed

● Highly rｅpetitｉve (ｈundｒedｓto milｌions)

--Shｏｒt sequeｎces in ｓａtｅlliｔeＤＮA

－－Sｅquenｃes of nｏrmal length in ｃerｔaｉｎ geｎｅs ｔｈａt exｉst in verｙ laｒge numbｅrｓ

C-vaｌue Parａdox

Ｔherｅ is apparently a lａck of aｓsｏciａｔion between C-value (the aｍoｕnt ｏｆＤNＡpresent iｎｔhｅｈaploid ｇeｎｏmｅｏf ｄiｆｆｅrent orgａnisms ）and the ｄegrｅe oｆoｒｇanismａl ｃompleｘity of ｖａrioｕs mulｔi-cellulａr oｒｇaniｓｍs． Iｎ１9７１, Thoｍas nａmed tｈｉsｐhｅｎoｍenon, “Ｃ-value Paｒaｄoｘ”．

在每一种生物中其单倍体基因组的DNＡ总量是特异的，被称为C值 (CＶａluｅ）。Ｃ值和生物结构或组成的复杂性不一致的现象称为Ｃ值悖论(Ｃ-value paｒadｏx）。

6.Hｙbridization

Hybｒidizatioｎ: the tｅcｈnique whereiｎｒｅnaｔured ＤNＡ is ｆormeｄ from seｐaraｔe siｎgl