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Hücre Biyolojisi HÜCRE BİYOLOJİSİ Makrotransfer Ders: 7 Dr. Öğretim Üyesi Banu EREN • MAKRO TRANSFER: • Su, yağlar, mineral madde iyonlarının hücre zarında değişiklik olmaksızın osmoz, difüzyon gibi olaylar ile hücreye girişine mikrotransfer denir. • İri moleküllü proteinler, karbonhidratlar, nükleik asitler, büyük partiküller, bakteriler ve başkaları aynı yolla hücreye girip çıkamazlar. • Büyük moleküllerin taşınıması için hücre zarı tarafından özel yöntemler geliştirilmiştir. 2 • Sitozis; genel olarak plazma zarından makro moleküllerin geçişine denir. Kütle transportu olarakta tanımlayabiliriz. • Endositozis hücre içine doğru geçişlere, • Ekzositozis ise hücreler arası boşluğa veya dışarıya doğru olan çıkışlara denir. 3 • Endositoz alınan maddelerin katı yada sıvı oluşuna göre ikiye ayrılır. • Pinositoz ve Fagositoz. • Her iki olayda da gelen madde hücre zarında ki reseptörlere bağlanarak hücre içine alınır. 4 • Pinositoz: Moleküller ve kolloidal eriyiklerin, proteinler, karbonhidratlar, yağlar gibi küçük damlacıklar halinde alınmasıdır. • Böyle bir madde kütlesi reseptör aracılığı ile hücre zarına bağlanınca zar bu kısımda çukurlaşmaya başlar. • Gelen madde reseptör ile birlikte bu çukura yerleşir. • Zarın çukurlaşması gittikçe artar ve sonuda bu kısım içindeki maddeler ile birlikte hücre zarından koparak ufak bir kese halinde (pinositoz vesikülü) sitoplazma ya geçer. 5 • Şekillenen pinositoz keseciklerinin çapına göre pinositoz ikiye ayrılır. • 1-)Mikro pinositoz (=kesecikler 0,1mikron dan daha küçük ise) • 2-)Makro pinositoz (=kesecikler 0,1 ile 1 mikron arasında ise) • Makro pinositoz da kesecikler vakuol düzeyindedir. Işık mikroskobunda görülebilir. • Mikropinositoz dan farklı olarak gelen maddeyi kavramak üzere yalancı ayaklar meydana gelebilir. 6 • Pinositoz vezikülleri çabuk gelişir. • Hücre içinde veziküller 3 şekilde sonuca ulaşır; 7 1)Veziküller değişmeden hücreyi geçerler= • Hücrede oluşan pinosotetik veziküller (pinosomlar) hücrelerin diğer tarafından tekrar hücreyi terk ederler. •Buna sitopompis =transsitozis denir. 8 2) Litik enzimlerin etkisiyle vezikül zarları parçalanarak birbirleriyle birleşirler. • Bu birleşme sonucu büyük vezikül ler oluşur. Bunlara endozom adı verilir. • Bu kesecikler lizozom ile birleşir ve böylece hücreye dışarıdan alınan maddeler alt birimlere ayrılır. (proteinler amino asitlere, polisakkaritler monosakkaritlere ayrılırlar.) • Bu alt birimler lizozomlardan sitosole verilirler ve burada hücre tarafından kullanılırlar. 9 • 3) Vezikül membranının çözülmesi ile vezikül hücre içine boşalır. 10 • Fagositoz: Katı haldeki maddelerin yani kolloidal partiküller, bakteriler, viruslar, yaşlanmış hücreler, ilaç gibi yapıların hücreye alınmasınıdır. • Pinositoza benzer. Hücre yüzeyi reseptörleri aracılık eder. Fakat alınan maddeler hem katı hem de iridir. • Şekillenen kesecikler daha büyüktür. (1 mikron ve yukarısı) Fagosite edilecek maddeye doğru yalancı ayaklar gönderilir. • Madde kütlesi yakalanır, hücre membranı kütle ile birlikte sitoplazma ya çöker. Bu kısım hücre membranın dan kopup ayrılır sitoplazma içinde fagositoz vakuolü şekillenmiş olur. • Bu tür vakuollere fagosom denir. 11 • Ekzositoz: Maddelerin makro moleküler, veziküler oluşumlar veya granüller halinde hücrelerden atılmasıdır. • Makromoleküler düzeyde olanlar fagosite edilmiş maddelere ait artıklardır. • Veziküller ile granüller ise hücrede salgılanıp dışarı verilen oluşumlardır. 12 Madde Alış Verişine Yardımcı Olan Morfolojik Değişmeler 1) Mikrovilus lar: • Hücre ile dış ortam arası alış veriş oranı hücre membranı nın genişliği ile doğru orantılıdır. Hücre yüzeyi ne kadar geniş olursa alış veriş miktarı o kadar fazla olur. • Sıvıları ve bunlarda erimiş halde bulunan maddeleri almakla görevli hücreler hücre hacmini değiştirmeksizin madde alış verişini kolaylaştırmak, alış kapasitesini artırmak amacıyla özel farklılaşmalar geliştirilmiştir. 13 2- Basal katlantılar: • Hücre membranı nın içe kıvrılması (=invaginasyon) ile oluşurlar. • Hücreler madde alış verişini artırmak için sadece serbest yüzeylerini değiştirmekle kalmayıp basal yüzleri de bu amaçla kullanabilirler. • Örneğin; böbrek proksimal tübüllerinde hücrelerin hem apikal yüzeyinde mikrovilus lar hem de basal yüzlerinde çok derin girintiler vardır. 14 3- Lateral katlantılar: • Yan yana gelen hücrelerin plasma zarları hücrelerin birbirlerine bağlanmasını sağlayan katlantılar yaparlar aynı zamanda yan yüzeylerinide genişletmiş olurlar. • Bunlar S veya Z şeklinde olabilirler. Hücreler bu şekille birbirlerine daha iyi ve daha sıkı tutunurlar. 15 • B-Hareket Sağlayan Değişmeler: • 1) Yalancı ayaklar: Topluluk halinde olmayan bağımsız hücrelerde rastlanır. Kalıcı oluşumlar değillerdir. Hücreler bu yolla yerlerini değiştirirler. Tek hücrelilerden amiplerde (protozoa) çok belirgindirler. • Bu harekete Ameboid hareket denir. Aynı zamanda beslenmelerini sağlarlar. • Çok hücreli organizmalarda savunmada görev alan hücrelerde bu harekete rastlanır. • (Nötrofil lerin kan dokudan bağ dokuya geçtiğinde yalancı ayaklarının oluşması, makrofaj ların savunma amaçlı yalancı ayak oluşumu gibi.) 16 • 2) Titrek tüyler: (Kinosilyum) • Bunlar yalancı ayaklardan farklı olarak kalıcı oluşumlardır. Bir birlik içinde bulunan hareketsiz hücrelerin lümene bakan yüzlerinde bulunurlar. • Bunlar da mikroviluslar gibi sitoplazmanın çıkıntılaşması=evaginasyon ile meydana gelirler. Ancak daha kalın (0.2) ve daha uzundurlar. • Bir hücre yüzeyinde düzgün sıralar halinde 250 veya daha fazla sayıda bulunabilirler. Tek silyumlu hücreler vardır. 17 • 3) Kamçılar: (Flagellum) Kamçılar titrek tüyler gibi kalıcı ve hareketli olan sitoplazmik oluşumlardır. • Kinosilyumlar ile aynı yapıyı gösterirler, fakat çok daha uzundurlar. • Memelilerde en güzel örnek spermatozoonun 40—50mikron uzunluğundaki kuyruğudur. Kamçılara daha çok tek hücrelilerde rastlanır. 18 • Stereosilyum: • Yapı olarak mikroviluslara benzer fakat uzunluk açısından silyumlara benzer. • Mikrotubulus ve basal cisimcik taşımaz ,hareketli değillerdir. • Aktin flaman ları içerir. Daha uzundurlar. Dallanma gösterirler. • Mikroviluslar gibi madde alış verişinde görevlidirler. • Stereosilyumlara organizmada sadece erkek genital sisteminde epididimis kanalını örten yüksek prizmatik epitel hücrelerinin apikal bölgesinde rastlanır. 19 C-Hücreyi Birbirine Bağlayan Değişimler: 20 • Bazı hücre türleri hücre örtüsü ile birlikte değişik yapı ve özellikte olan hücre bağlantılarına sahiptirler. • Bağlanma işleminin yanı sıra maddelerin hücrelerden içe veya dışa geçişlerini sağlarlar. Komşu hücreler arasında madde iletimini gerçekleştirmede önemli rolleri vardır. Belli başlıları şunlardır; 21 • *Zonula Ocludens (Z.O.) (taç tabaka) • *Zonula Adherens (Z.A.) (yapıştırıcı tabaka) • *Makula Adherens M.A. yapıştırıcı düğme Desmozom apikale yakın yerde bulunur. • *Hemidesmozom (H.D.) Basal bölümde yer alırlar. • *Gap Juction (Neksus) (N) • *Lateral Katlantılar (L.K.) 22 • Işık mikroskobu ile örtü epitel hücrelerini incelersek komşu hücrelerin apikal uçları arasında koyu birer çizgi bulunduğunu görürüz. • Bu kısma Terminal Bar denir. • Elektron mikroskobunda ise daha kompleks bir yapı gösterir. • Bağlayıcı kompleksler denir iki yada üç bağlantı türü yer alır. • En güzel tek katlı prizmatik epitelde gözlenir. 23 • Hücre arası bağlantılar yapı ve işlevlerine göre üçe ayrılır; • 1-Geçirgenliği engelleyen bağlantılar:Z.O. • 2-Hücrelerin birbirine yapışmasını sağlayan bağlantılar: Z A.- MA.- H D. • • 3-Hücrelerin ara iletimini sağlayan bağlantılar: Neksus. – Kimyasal sinaps 24 • Zonula Ocludens(Z.O.): Epitel hücreleri arasında glikokaliks (hücre örtüsü) içeren bir açıklık bulunur. • Apikal bölümde uçlarında daralmalar ve kaynaşmalar olur. • Aralık tamamen kapanır. • Terminal barın en yüzeyindeki bu kısmına zonula ocludens denir. • Sıkı bir şekilde kaynaştıklarından sıkı bağlantı (Tight Junction) adı da verilebilir. 25 • Komşu iki membrandaki iri integral protein molekülleri karşılıklı çıkıntılar yaparlar. • Bu simetrik çıkıntılar fermuar gibi birbirlerinin aralarına girerek iki membranı birbirine sıkıca bağlarlar. (klaudin ve okludin proteinler) • Hücreler arası mesafeyi lümene kapalı tutarlar. Maddeler lümenden hücre arasına geçemezler. • Bu nedenle apikal yüzeyi kullanırlar. Bulundukları hücreleri kemer gibi sararlar. 26 • Zonula Adherens(Z.A.): Z.O. in hemen altında bulunurlar. Bunlarda hücreyi kemer gibi sararlar. Yalnız hücre membranları birbiri ile kaynaşmaz. • Aralarında 200Ao luk bir mesafe kalır. Glikokaliks bu bölgede daha da yoğundur. Siyalik asitçe zengindir. • Apikal bölgedeki terminal ağdan gelen aktin mikroflamanları hücrelerin birbirine tutunmasını sağlar. • Gelen flamanlar zonula adherens bölgesine dirsek yaparak dönerler. (kancalanırlar). Üretilen gücün bitişik hücreye geçmesini sağlarlar. 27 • Transmembran yapışma proteinleri kadherinler aracılığıyla birbirine tutunur. • Kadherinler hücre içi uzantıları aktin filamentlerine bağlanan kateninler, vinkulin ve alfa-aktinin gibi hücre içi kenetlenme proteinlerine tutunur. • Ör. Aktinlerin belirli bir bölgede kasılması ile her bir hücrenin apikali daralır. 28 • Makula Adherens(M.A.)(=Desmozom) Z.A. Z.O. in hemen altında yer alır. Bunlardan ayrı olarak ta bulunabilir. Örneğin; epidermisin strasum spinosum hücrelerinde çok görülür. • Desmozomlar hücrelerin çevresini tamamen sarmazlar. Hücreler arası aralık daha geniştir. Ortasında çizgi halinde daha yoğun bir bölge vardır. • Hücre membranının sitoplazma ya bakan yüzünde de yoğun bir maddeden oluşmuş plak vardır. 29 • Bu plakalar plakoglobin ve desmoplakin adı verilen hücre içi kenetlenme
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