6 research outputs found
Molecular machinery of a membrane-bound proton pump : Studies of charge transfer reactions in cytochrome c oxidase
In cellular respiration, electron transfer from the breakdown of foodstuff is coupled to the formation of an electrochemical proton gradient. This is accomplished through proton translocation by respiratory complexes, and the proton gradient is subsequently used e.g. to drive ATP production. Consequently, proton- and electron-transfer reactions through the hydrophobic interior of membrane proteins are central to cellular respiration. In this thesis, proton- and electron transfer through an aa3-type terminal oxidase, cytochrome c oxidase (CytcO) from Rhodobacter sphaeroides, have been studied with the aim of understanding the molecular proton-transfer machinery of this proton pump. In the catalytic site of CytcO the electrons combine with protons and the terminal electron acceptor O2 to form water in an exergonic reaction that drives proton pumping. Therefore, CytcO must transfer both protons that are pumped and protons for the oxygen chemistry through its interior. This is done through its two proton-transfer pathways, termed the D pathway and the K pathway. Our studies have shown that the protons pumped during oxidation of CytcO are taken through the D pathway, and that this process does not require a functional K pathway. Furthermore, our data suggests that the K pathway is used for charge compensation of electron transfer to the catalytic site, but only in the A2 â P3 state transition. Our data also show that the water molecules identified in the crystal structures of CytcO play an important role in proton transfer through the D pathway. Finally, the effects of liposome reconstitution of CytcO on D-pathway proton transfer were investigated. The results suggest that the membrane modulates the rates of proton transfer through the D pathway, and also influences the extent of electron transfer between redox-active sites CuA and heme a
Learning from macro to micro : Use of animations in biology teaching
Animationer Àr ett allt vanligare inslag i biologiundervisningen, inte minst för att visa molekylÀra processer som Àr svÄra att förstÄ utifrÄn 2-dimensionella stillbilder. I denna studie undersöks hur en animation kan anvÀndas av elever för att studera fotosyntes frÄn ekosystem till molekyl. Tre elever som lÀser Biologi 2 pÄ gymnasiet har fÄtt ta del av en animation och sedan diskuterat denna utifrÄn en elevuppgift. Uppgiften var utformad för att belysa olika biologiska organisationsnivÄer. Elevernas diskussion spelades in, transkriberades och sammanstÀlldes med fÀltanteckningar frÄn diskussionen. Materialet har sedan analyserats, dels utifrÄn elevernas samtalsform med det teoretiska ramverket exploratory talks och dels utifrÄn elevernas förmÄga att se hur strukturer och funktioner Àr sammanlÀnkade över olika nivÄer med ramverket systems thinking. Resultaten visar att en stor del av elevernas samtal uppvisade kÀnnetecken pÄ exploratory talk, vilket ger goda förutsÀttningar för lÀrande i grupp. Eleverna diskuterade ocksÄ strukturer och funktioner som Àr involverade i fotosyntesen pÄ ett sÀtt som tyder pÄ systems thinking. Resultaten indikerar att en animation med pÄföljande diskussion utifrÄn en elevuppgift gav goda förutsÀttningar för elever att utforska fotosyntesen som system och att diskutera fotosyntesen som energiprocess pÄ olika biologiska organisationsnivÄer