Qhov Tseem Ceeb Qhov txawv - Alpha Helix vs Beta Pleated Sheet
Alpha helices thiab beta pleated nplooj ntawv yog ob feem ntau pom cov txheej txheem thib ob hauv cov saw hlau polypeptide. Ob yam khoom siv no yog thawj kauj ruam tseem ceeb hauv cov txheej txheem ntawm folding ib txoj hlua polypeptide. Qhov sib txawv tseem ceeb ntawm Alpha Helix thiab Beta Pleated Sheet yog nyob rau hauv lawv cov qauv; lawv muaj ob daim duab sib txawv los ua txoj haujlwm tshwj xeeb.
Alpha Helix yog dab tsi?
Ib qho alpha helix yog txoj cai-tes ntawm cov amino acid residues ntawm cov saw hlau polypeptide. Qhov ntau ntawm cov amino acid residues tuaj yeem sib txawv ntawm 4 mus rau 40 residues. Cov hydrogen bonds tsim ntawm cov pa oxygen ntawm C=O pab pawg nyob rau sab saum toj coil thiab hydrogen ntawm N-H pab pawg neeg hauv qab coil pab tuav lub kauj ua ke. Ib daim ntawv cog lus hydrogen yog tsim rau txhua plaub cov amino acid residues nyob rau hauv cov saw raws li saum toj no. Cov qauv zoo li no muab nws cov yam ntxwv meej xws li lub thickness ntawm lub kauj thiab nws dictates qhov ntev ntawm txhua qhov tig raws lub helix axis. Kev ruaj ntseg ntawm alpha helix qauv nyob ntawm ntau yam.
O atoms hauv liab, N atoms xiav, thiab hydrogen bonds li ntsuab dotted kab
Dab tsi yog Beta Pleated Sheet?
Beta pleated sheet, tseem hu ua beta sheet, yog suav tias yog daim ntawv thib ob ntawm cov qauv hauv cov protein. Nws muaj cov beta strands uas txuas tom qab los ntawm qhov tsawg kawg nkaus ntawm ob lossis peb lub caj qaum hydrogen bonds los ua ib daim ntawv sib tw, pleated raws li qhia hauv daim duab. Ib qho beta strand yog ib qho stretch ntawm polypeptide saw; nws qhov ntev yog feem ntau sib npaug li 3 txog 10 amino acids, nrog rau cov pob txha caj qaum hauv qhov kev lees paub txuas ntxiv.
4-stranded antiparallel β daim ntawv tawg ntawm cov qauv siv lead ua ntawm cov enzyme catalase.
a) uas qhia txog kev tiv thaiv tsis sib luag hydrogen bonds (dotted) ntawm peptide NH thiab CO pawg ntawm cov kab uas nyob ib sab. Cov xib xub qhia cov kev taw qhia saw, thiab electron ceev contours qhia cov tsis-H atoms. O atoms yog pob liab, N atoms yog xiav, thiab H atoms raug tshem tawm kom yooj yim; sidechains tsuas yog qhia tawm rau thawj sidechain C atom (ntsuab)
b) Ntug-ntawm saib ntawm nruab nrab ob β strands
Hauv cov nplooj ntawv beta pleated, cov saw hlau polypeptide khiav ib sab. Nws tau txais lub npe "daim ntawv pleated" vim qhov zoo li nthwv dej ntawm cov qauv. Lawv txuas ua ke los ntawm hydrogen bonds. Cov qauv no tso cai rau tsim ntau cov ntawv cog lus hydrogen los ntawm kev nthuav tawm cov saw hlau polypeptide.
Qhov txawv ntawm Alpha Helix thiab Beta Pleated Sheet yog dab tsi?
qauv ntawm Alpha Helix thiab Beta Pleated Sheet
Alpha Helix:
Nyob rau hauv cov qauv no, cov pob txha polypeptide yog nruj nreem khi nyob ib ncig ntawm lub axis xav li ib tug kauv qauv. Nws tseem hu ua helicoidal kev npaj ntawm peptide saw.
Qhov tsim ntawm alpha helix qauv tshwm sim thaum cov saw hlau polypeptide tau twisted rau hauv ib lub kauv. Qhov no ua rau tag nrho cov amino acids nyob rau hauv cov saw hlau tsim hydrogen bonds (ib qho kev sib txuas ntawm cov pa molecule thiab hydrogen molecule) nrog rau ib leeg. Cov ntawv cog lus hydrogen tso cai rau lub helix los tuav lub kauv zoo thiab muab lub kauj nruj. Cov kauv zoo li no ua rau alpha helix muaj zog heev.
Hydrogen bonds yog qhia los ntawm cov dots daj.
Beta Pleated Sheet:
Thaum ob lossis ntau qhov tawg ntawm cov saw hlau polypeptide sib tshooj nrog ib leeg, tsim cov kab ntawm hydrogen bonds nrog ib leeg, cov qauv hauv qab no tuaj yeem pom. Nws tuaj yeem tshwm sim hauv ob txoj kev; parallel arrangement thiab anti-parallel arrangement.
Piv txwv ntawm cov qauv:
Alpha Helix: Cov ntiv tes lossis cov ntiv taw tuaj yeem coj los ua piv txwv ntawm alpha helix qauv.
Beta Pleated Sheet: Cov qauv ntawm cov plaub zoo ib yam li cov qauv ntawm beta pleated sheet.
Cov yam ntxwv ntawm tus qauv:
Alpha Helix: Hauv alpha helix qauv, muaj 3.6 amino acids ib tig ntawm lub helix. Tag nrho cov peptide bonds yog trans thiab planar, thiab N-H pawg nyob rau hauv peptide bonds taw tes rau tib qho kev taw qhia, uas yog kwv yees li thaum uas tig mus rau lub axis ntawm lub helix. Cov pab pawg C=O ntawm tag nrho cov peptide bonds taw tes rau hauv qhov kev taw qhia, thiab lawv nyob rau tib lub axis ntawm lub helix. Pawg C=O ntawm txhua daim ntawv cog lus peptide yog sib koom ua ke rau N-H pawg ntawm peptide daim ntawv cog lus ua ib daim ntawv cog lus hydrogen. Tag nrho cov R- pab pawg tau taw qhia sab nraud los ntawm lub helix.
Beta Pleated Sheet: Txhua daim ntawv cog lus peptide hauv daim ntawv beta pleated yog cov qauv thiab muaj qhov sib txawv. C=O thiab N-H pawg ntawm peptide bonds los ntawm cov saw hlau uas nyob ib sab yog nyob rau hauv tib lub dav hlau thiab taw tes rau ib leeg ua hydrogen bonding ntawm lawv. Tag nrho cov R- pawg nyob rau hauv ib qho kev sib txuas tuaj yeem tshwm sim saum toj thiab hauv qab ntawm lub dav hlau ntawm daim ntawv.
Definition:
Cov qauv theem nrab: Nws yog cov duab ntawm cov folding protein vim hydrogen bonding ntawm nws cov pob txha amide thiab carbonyl pawg.
