Isakhiwo kanye Nomsebenzi We-Ribosomes
Ama-Ribosome angenye yama-organelle abaluleke kakhulu ngaphakathi kwamaseli, adlala indima eqondile ekwakhiweni kwamaprotheni. Amaphrotheni angama-molecule ayinhloko abhekene cishe nayo yonke imisebenzi yezinto eziphilayo, kusukela ekwakheni izakhiwo zamaseli, ukusheshisa ukusabela kwamakhemikhali ngama-enzyme, ukulawula ukudluliselwa kwesignali phakathi kwamaseli, kanye nokusiza ekuvikeleni komzimba. Ngakho-ke, ukuqonda isakhiwo kanye nomsebenzi wama-ribosome kusho ukuqonda esinye sezikhungo zomsebenzi wokuphila ezingeni lama-molecule.
Ukuqonda ama-Ribosome
Ama-Ribosome ayizinhlanganisela zama-macromolecular ezakhiwe yi-ribosomal RNA (rRNA) kanye namaprotheni e-ribosomal. Ama-Ribosome atholakala kuzo zonke izinhlobo zamaseli—kokubili ama-prokaryotes (njengamabhaktheriya) kanye nama-eukaryotes (njengezilwane, izitshalo, kanye nesikhunta). Ukuhluka kwama-ribosome kusekwakhekeni kwawo: i-rRNA akuyona nje ingxenye yesakhiwo kodwa futhi idlala indima yokuvuselela ekwakhekeni kwama-peptide bonds. Ngamanye amazwi, ama-ribosome angacatshangwa njengemishini "yebhayoloji" ehumusha ulwazi lwezakhi zofuzo oluvela ku-mRNA luye ku-amino acid sequences ezakha amaprotheni.
Isakhiwo Esiyisisekelo Sama-Ribosome
Ngokuvamile, ama-ribosome aqukethe ama-subunit amabili: i-subunit encane kanye ne-subunit enkulu. Lawa ma-subunit amabili ayahlangana ngesikhathi sokuhumusha (ukuhumusha i-mRNA) futhi ahlukane uma engasebenzi. I-subunit ngayinye yakhiwe yi-rRNA kanye neprotheni ngezilinganiso ezithile.
Ama-Ribosome kuma-Prokaryotes (70S)
Kumaseli e-prokaryotic, ama-ribosome kuthiwa angama-70S ngobukhulu (i-S iyiyunithi ye-Svedberg ekhombisa izinga lokusatshalaliswa ngesikhathi sokugeleza, hhayi isilinganiso esiqondile sobude). Ama-ribosome e-70S aqukethe:
– I-subunit encane ye-30S, equkethe i-16S rRNA kanye nenani lamaprotheni.
– I-subunit enkulu yama-50S, equkethe ama-23S kanye nama-5S rRNA kanye namaprotheni e-ribosomal.
I-subunit encane idlala indima ebalulekile ekuqaphelweni kwe-mRNA nasekunqumeni indawo yokuqala yokuhumusha, kuyilapho i-subunit enkulu iyindawo eyinhloko yokwakheka kwesibopho se-peptide.
Ama-Ribosome kuma-Eukaryotes (80S)
Kumaseli e-eukaryotic, ama-ribosome angama-80S ngobukhulu, akhiwa yi:
– Iyunithi encane engu-40S, equkethe i-18S rRNA.
– Iyunithi encane enkulu yama-60S, equkethe i-28S, 5.8S, kanye ne-5S rRNA.
Ama-ribosome e-eukaryotic ngokuvamile ayinkimbinkimbi kakhulu, aqukethe amaprotheni e-ribosomal amaningi kanye nezici ezengeziwe ezilawula inqubo yokuhumusha.
Indawo yamaRibosome kumaSeli
Ama-Ribosome angatholakala ezindaweni ezimbili eziyinhloko:
1. Ama-ribosome amahhala ku-cytoplasm
Ama-ribosome amahhala ngokuvamile akhiqiza amaprotheni azosetshenziswa ku-cytosol, isibonelo ama-enzyme e-metabolic noma amaprotheni esakhiwo seli.
2. Ama-Ribosome aboshwe kwi-rough endoplasmic reticulum (rough ER)
Ama-ribosome anamathele ku-rough ER avame ukukhiqiza amaprotheni okumele akhishwe esitokisini, afakwe kulwelwesi lweseli, noma alethwe kuma-organelle athile njenge-lysosomes. Ama-ribosome anamathela ngoba i-rough ER inama-receptor asebenzisana nama-ribosome lapho uchungechunge lwe-polypeptide olukhiqizwayo luqukethe isignali ethile (i-signal peptide).
Ngaphezu kwalokho, ama-organelle afana ne-mitochondria nama-chloroplast nawo anama-ribosome awo, afana kakhulu nama-ribosome e-prokaryotic (70S). Lokhu kusekela inkolelo-mbono ye-endosymbiosis, ethi i-mitochondria nama-chloroplast avela ezintweni eziphilayo ze-prokaryotic ezaziphila ngokubambisana ngaphakathi kwamaseli okhokho be-eukaryotic.
Izingxenye ze-Ribosome: i-rRNA kanye neProtheyini
Ama-Ribosome akhiwa izingxenye ezimbili eziyinhloko:
– I-Ribosomal RNA (rRNA): Lolu uhlobo oluyinhloko lwe-RNA futhi lwakha uhlaka kanye nesikhungo sokulungisa i-ribosome. I-rRNA inesibopho sokuvuselela ukwakheka kwezibopho ze-peptide (umsebenzi we-peptidyl transferase).
– Amaprotheni e-ribosomal: asebenza ekuqiniseni isakhiwo se-rRNA, asiza ukuhlanganisa ama-subunit, futhi asebenzisane nezici zokuhumusha.
Inhlanganisela ye-rRNA namaprotheni yakha isakhiwo esiqondile esinezinhlangothi ezintathu, okuvumela ama-ribosome ukuthi asebenze ngokushesha nangokunembile.
Izindawo Ezisebenzayo Ngaphakathi Kwe-Ribosomes
Uma i-ribosome ihumusha ngenkuthalo, kunezindawo ezintathu eziyinhloko ezibaluleke kakhulu, ikakhulukazi ku-subunit enkulu:
1. Indawo A (indawo ye-Aminoacyl)
Indawo yokungena ye-tRNA ethwala ama-amino acid ngokwe-mRNA codon.
2. Indawo ye-P (indawo ye-Peptidyl)
Indawo ye-tRNA ethwele uchungechunge lwe-polypeptide olukhulayo.
3. Indawo E (Indawo yokuphuma)
Indawo lapho i-tRNA ekhiphe ama-amino acid iphuma khona.
Ukuhamba kwe-tRNA kusuka ku-A kuya ku-P bese kuba ku-E kwenzeka njengoba i-ribosome “ifunda” izisekelo ezintathu ze-mRNA ngesikhathi (i-codon yi-codon).
Umsebenzi wamaRibosome ekwenziweni kwamaphrotheni
Umsebenzi oyinhloko wama-ribosomes ukuhumusha, okuhumusha ukulandelana kwe-nucleotide ku-mRNA kube ukulandelana kwe-amino acid. Ukuhumusha ngokuvamile kuhlukaniswe ngezigaba ezintathu:
1. Ukuqaliswa
Kulesi sigaba, i-subunit encane ye-ribosome inamathela ku-mRNA bese ifuna i-start codon (ngokuvamile i-AUG). I-initiator tRNA ephethe i-methionine nayo iyajoyina. Uma i-start codon isisendaweni, ama-subunit amakhulu ayahlangana ukuze akhe i-ribosome esebenzayo.
2. Ukwelula
I-ribosome ihamba nge-mRNA, yandisa uchungechunge lwe-polypeptide. I-tRNA ephethe i-amino acid ingena endaweni ye-A, lapho inamathela khona ochungechungeni oluku-P site. I-ribosome ibe isishintsha i-codon eyodwa, isuse i-tRNA futhi yenze indawo ye-tRNA elandelayo.
3. Ukuqeda
Uma i-ribosome ihlangana ne-stop codon (UAA, UAG, noma i-UGA), ayikho i-tRNA ehambisanayo yaleyo codon. Esikhundleni salokho, i-termination factor ingena futhi ibangele ukukhishwa kwe-polypeptide chain. I-ribosome ibe isihlukana ibe ama-subunit amabili futhi ilungele ukusetshenziswa kabusha.
Ama-Ribosome njengezinhloso ze-Antibiotic
Ama-ribosome e-prokaryotic ahlukile ngokwesakhiwo kuma-ribosome e-eukaryotic. Lo mehluko usetshenziswa kwezokwelapha ngoba amanye ama-antibiotic angavimbela ama-ribosome ebhaktheriya ngaphandle kokulimaza kakhulu ama-ribosome abantu. Isibonelo:
– I-Tetracycline ivimbela ukungena kwe-tRNA endaweni ye-A.
– I-Chloramphenicol ivimbela umsebenzi we-peptidyl transferase.
– I-Streptomycin ingabangela ukufundwa kabi kwe-mRNA.
Kodwa-ke, ukusetshenziswa kwama-antibiotic kumele kube okufanele ngoba amabhaktheriya angakha ukumelana ngokuguquka kwezakhi zofuzo noma ezinye izindlela zokuzivikela.
Isiphetho
Ama-Ribosome ayizitho ezibalulekile ezisebenza njengendawo yokwenziwa kwamaprotheni. Isakhiwo se-ribosome sakhiwe ngama-subunit amabili, elikhulu nelincane, kanti izingxenye eziyinhloko ziyi-rRNA kanye namaprotheni e-ribosomal. Ama-Ribosome anezindawo ze-A, P, kanye ne-E, eziqinisekisa inqubo yokuhumusha ehlelekile nenembile. Ngaphandle kokudlala indima ebalulekile ekukhiqizweni kwamaprotheni ezidingweni zamaseli, ama-ribosome aphinde aqondiswe ngama-antibiotic ahlukahlukene ngenxa yomehluko phakathi kwama-ribosome e-prokaryotic kanye ne-eukaryotic. Ngokuqonda isakhiwo kanye nomsebenzi wama-ribosome, singabona ukuthi izinqubo eziyisisekelo ezisekela ukuphila ziyinkimbinkimbi futhi zihlelwe kanjani.
