Carotenoids as accessory and protective pigments in photosynthesis

Fotosinteza je neophodan i izuzetno složen biokemijski proces u biljkama. Odvija se u reakcijskim centrima smještenim na tilakoidnim membranama kloroplasta. Razlikujemo dva reakcijska centra biljaka – PSII i PSI. Na PSII se stvara protonski gradijent, formira se O2 i oslobađa se e- koji se potom prenosi do PSI. Mehanizmi zaštite fotosustava omogućuju jednolik prijenos energije na reakcijske centre i optimalan tijek elektrona među njima. Zbog svoje građe PSII je podložan oksidaciji koja rezultira gubitkom funkcije, u čijem sprečavanju vrlo važnu ulogu imaju pomoćni i zaštitni pigmenti poput karotenoida. Karotenoidi se javljaju već kod prvih bakterija i prisutni su u svim carstvima, u fotosintetskim i u nefotosintetskim organizmima. Karotenoidi, klorofili i proteini zajedno tvore antenske komplekse koji služe za sakupljanje svjetlosne energije i njezin prijenos na reakcijske centre. Kao dio antenskih kompleksa, karotenoidi imaju ulogu pomoćnih pigmenta za sakupljanje svjetlosne energije i njezin prijenos do klorofila a te ulogu zaštitnih pigmenata koji sprečavaju oksidaciju reakcijskog centra. Naime, zbog građe u obliku linearnih organskih molekule s višestruko konjugiranim dvostrukim vezama, pi konjugirane strukture, mogu prenositi energiju koju apsorbiraju do molekula klorofila a u reakcijskom centru ili preuzeti višak energije s reakcijskog centra, te zahvaljujući antioksidativnom djelovanju mogu spriječiti oštećenja uzrokovana reaktivnim oblicima kisika na reakcijskom centru i tilakoidnim membranama. Važnu ulogu u zaštiti od oštećenja fotosistema oksidacijom ima ksantofilski ciklus čije su komponente poznate ali nedostaje cjelovit biofizički mehanizam.Photosynthesis is a vital and complex biochemical process that occurs in the reaction centers of the chloroplast thylakoid membranes in plants. There are two reaction centers – PSII and PSI. PSII establishes proton gradient, creates oxygen and releases electrons that are subsequently transferred to PSI. Photosystem protection mechanisms allow a balanced energy transfer between reaction centers and an optimal electron flow. Due to its built PSII is susceptible to oxidation that leads to a loss of function. Accessory and protective pigments such as carotenoids have a great contribution in stopping oxidation. Carotenoids were first developed in early bacteria and now they are present in all domains, both in photosynthetic and non-photosynthetic organisms. Carotenoids, chlorophylls and proteins together form antenna complexes that are used to harvest light and transfer its energy on the reaction centers. The role of carotenoids in antenna complexes is that of accessory pigments harvesting energy and transferring it on chlorophyll a molecules. Besides being accessory pigments, as protective pigments they have a role in protecting reaction centers from oxidation. Due to their linear molecular structure that contains multiple conjugated double bonds, called piconjugated system, they can either transfer absorbed energy toward chlorophyll a reaction center molecule or accept excess reaction center energy. They can also stop the damage from reactive oxygen species on reaction centers and thylakoid membranes due to their antioxidative abilities. Protection from oxidative damage of photosystem is mainly provided by xanthophyll cycle. Main components of the cycle are quite known but the actual biophysicalmechanism is not yet derived

Signal Recovery on Graphs: Random versus Experimentally Designed Sampling

We study signal recovery on graphs based on two sampling strategies: random sampling and experimentally designed sampling. We propose a new class of smooth graph signals, called approximately bandlimited, which generalizes the bandlimited class and is similar to the globally smooth class. We then propose two recovery strategies based on random sampling and experimentally designed sampling. The proposed recovery strategy based on experimentally designed sampling is similar to the leverage scores used in the matrix approximation. We show that while both strategies are unbiased estimators for the low-frequency components, the convergence rate of experimentally designed sampling is much faster than that of random sampling when a graph is irregular. We validate the proposed recovery strategies on three specific graphs: a ring graph, an Erd\H{o}s-R\'enyi graph, and a star graph. The simulation results support the theoretical analysis.Comment: Correct some typo

Black Hole Mass Estimation in Type 1 AGN: Hβ\beta vs. Mg II lines and the role of Balmer continuum

Here we investigate the H$\beta$ and Mg II spectral line parameters used for the black hole mass (M$_{\rm BH}$) estimation for a sample of Type 1 Active Galactic Nuclei (AGN) spectra selected from the Sloan Digital Sky Survey (SDSS) database. We have analyzed and compared the virialization of the H$\beta$ and Mg II emission lines, and found that the H$\beta$ line is more confident virial estimator than Mg II. We have investigated the influence of the Balmer continuum emission to the M$_{\rm BH}$ estimation from the UV parameters, and found that the Balmer continuum emission can contribute to the overestimation of the M$_{\rm BH}$ on average for ~ 5% (up to 10%).Comment: 9 pages, 3 figures, Accepted for publication in Frontiers in Astronomy and Space Science