A three-state model with loop entropy for the over-stretching transition of DNA

We introduce a three-state model for a single DNA chain under tension that distinguishes between B-DNA, S-DNA and M (molten or denatured) segments and at the same time correctly accounts for the entropy of molten loops, characterized by the exponent c in the asymptotic expression S ~ - c ln n for the entropy of a loop of length n. Force extension curves are derived exactly employing a generalized Poland-Scheraga approach and compared to experimental data. Simultaneous fitting to force-extension data at room temperature and to the denaturation phase transition at zero force is possible and allows to establish a global phase diagram in the force-temperature plane. Under a stretching force, the effects of the stacking energy, entering as a domain-wall energy between paired and unpaired bases, and the loop entropy are separated. Therefore we can estimate the loop exponent c independently from the precise value of the stacking energy. The fitted value for c is small, suggesting that nicks dominate the experimental force extension traces of natural DNA.Comment: 12 pages, 5 figures + Supplementary informatio

Helmut Karzel (1928-2021)

Obituary for Professor Dr. Dr. h.c. Helmut Karzel, who passed away on June 22, 2021, at the age of 93

Vitamin E-Gehalt der Kuhmilch in Abhängigkeit von der Grasfütterung im Tal und auf alpinen Weiden

Jeweils sechs laktierende Brown Swiss Kühe erhielten entweder reine Weidefütterung, reine Grünfütterung im Stall oder eine konventionelle Silage-Kraftfutter Vergleichsration. Dies wurde nacheinander für jeweils 42 Tagen an einem raigrasreichen Talstandort (400 m) und auf einer extensiven artenreichen Alpweide (2000 m) durchgeführt. Die Konzentration an Tocopherolen (Vitamin E)in der Milch wurde mittels HPLC bestimmt. Die Vitamin E-Konzentrationen waren in den grasbasierten gegenüber den aus der Vergleichsration stammenden Milchproben generell deutlich erhöht. Einen weiteren geringen Zusatzeffekt für den Tocopherolgehalt der Milch brachte die Alpweide, wobei jedoch aufgrund der geringeren Milchleistung die tägliche Menge an mit der Milch sekretiertem Vitamin E geringer war als auf der Talweide

Artenreiches Rauhfutter als Alleinfutter und Fettsäurenmuster der Milch

In two experiments it was investigated which factors to what extent determine the fatty acid composition milk when cows are grazing high alpine pastures. The influences of altitude per se, of alpine forage quality, of concentrate-free diet type and of the overall grazing effect were separated by the experimental design. The most important factor which significantly elevated the concentrations of CLA, α-linolenic acid (ALA) and n-3 PUFA in milk fat was found to be the alpine diet type, i.e. the feeding of roughage-only (as well hay as pasture of as well lowland as alpine origin) with omission of concentrates and maize. Additionally a clear positive effect of the forage quality of alpine pastures on ALA concentration in milk fat was found. The latter effect is assumed to be linked to specific plant ingredients (eg. tannins) and to the low energy density of the alpine flora, which may influence the ruminal biohydrogenation of native ALA. An effect of altitude per se (hypoxia) was not found

A study on the causes for the elevated n−3 fatty acids in cows' milk of alpine origin

The influence of grass-only diets either from rye-grass-dominated lowland pastures (400 m above sea level) or botanically diverse alpine pastures (2000 m) on the FA profile of milk was investigated using three groups of six Brown Swiss cows each. Two groups were fed grass-only on pasture (P) or freshly harvested in barn (B), both for two experimental periods in the lowlands and, consecutively, two periods on the alp. Group C served as the control, receiving a silage-concentrate diet and permanently staying in the lowlands. Effects of vegetation stage or pasture vs. barn feeding on milk fat composition were negligible. Compared with the control, α-linoleic acid (18∶3n−3) consumption was elevated in groups P and B (79%, P<0.001) during the lowland periods but decreased on the alp to the level of C owing to feed intake depression and lower 18∶3n−3 concentration in the alpine forage. Average 18∶3n−3 contents of milk fat were higher in groups, P and B than in C by 33% (P<0.01) at low and by 96% (P<0.001) at high altitude, indicating that 18∶3n−3 levels in milk were to some extent independent of 18∶3n−3 consumption. The cis-9,trans-11 CLA content in milk of grass-fed cows was higher compared with C but lower for the alpine vs. lowland periods whereas the trans-11, cis-13 isomer further increased with altitude. Long-chain n−3 FA and phytanic acid increased while arachidonic acid decreased with grass-only feeding, but none of them responded to altitude. Grass-only feeding increased milk α-tocopherol concentration by 86 and 134% at low and high altitude (P<0.001), respectively. Changes in the ruminal ecosystem due to energy shortage or specific secondary plant metabolites are discussed as possible causes for the high 18∶3n−3 concentrations in alpine mil

The Measurement of pO2 by O2 Electrode in the Presence of Changing pCO2

Studies on the transport of O2 and CO2 in the alveoli and blood have focused on simultaneous measurements of the two gases with classical instruments; an interaction between the two gases has been assumed (see Bohr Effect and Rahn-Otis Plot). Nevertheless, of late years with wide use of the Kimmich-Kreuzer Oxygen Electrode in liquids and gases, the measurements have included oxygen alone. These small (2mm) polarographic catheter electrodes have been used in both physiologic and bioengineering applications. Within a particular range of polarization voltage, the electrode current is limited by O2 diffusion across a membrane; i.e., at a constant polarization voltage, current is linearly related to pO2. Since it is often the case that measurements of pO2 are taken while pCO2 is changing, CO2 effects on the electrode current should be known and corrected for. In the present experiments, electrical currents at 5% and 21% O2 with varying amounts of CO2 were measured. Polarograms (a plot of current v. voltage) made in the presence and absence of CO2 were compared. The pO2 measurement is significantly affected by CO2 at 21% O2, but not a 5% O2; i.e., the O2 value changed with different CO2 levels. These results are particularly interesting since the electrode membrane is a physical model of the alveolar membrane

Influence of feeding Mediterranean food industry by-products and forages to Awassi sheep on physicochemical properties of milk, yoghurt and cheese

Feeding agro-industrial by-products and unconventional forages, rich in potentially anti-nutritional factors, may influence the quality of the raw milk and the dairy products prepared therefrom. The aim of the present study was to determine side-effects on physicochemical properties of milk, yoghurt and cheese of feeding diets where one third were feeds either rich in lipids (tomato pomace and olive cake) or phenols (olive leaves and lentil straw) or electrolytes (Atriplex leaves). The diets, including a control diet, were designed to be isoenergetic and isonitrogenous. They were fed in amounts of 2 5 kg dry matter/day per head during 50 days to 6×10 multiparous fat-tailed Awassi ewes. Milk samples were analysed for various physicochemical traits and fatty acid composition on days 0, 24, 36 and 48. Three times, milk pooled by group was processed to yoghurt and non-aged farmer-type cheese, which were analysed for their gross and fatty acid composition and texture, and were subjected to sensory evaluation. Feeding olive cake and tomato pomace reduced milk casein, but increased proportions of monounsaturated fatty acids. There were some variations in minerals among test diets but, contrary to expectations, Atriplex did not increase milk sodium. The nutritional composition of yoghurt and cheese was not varied much by the test feeds, except for some changes in fatty acid profile similar to the milk. Yoghurt firmness declined with all test diets, but texture score tended to be lower only for olive cake and leaf diets relative to control. Cheese firmness was increased by feeding the Atriplex leaf and olive cake diets which was also reflected in the texture scores. No off-flavours were reported. Possible reasons for effects on the dairy products are discussed. In conclusion, the feeds investigated had certain effects on the physicochemical properties of dairy products, but these were neither very systematic nor large thus not prohibiting their use in Mediterranean sheep milk production system