Diane Johnson

[15] Isolation of liver or kidney mitochondria

Publisher Summary This chapter describes the isolation of liver or kidney mitochondria. The selected tissue is disrupted by homogenization in cold isotonic sucrose. Differential centrifugation is then employed to separate the mitochondria from cell debris, red blood cells, nuclei, microsomes, and soluble components. For the isolation of liver mitochondria, the homogenate is distributed into Lusteroid centrifuge cups and centrifuged at 600 g for 10 minutes. The supernatant fraction is decanted and saved. The pellets may be dispersed by using the side of a stirring rod against the wall of the cup or by handoperating the homogenizer. The resuspended material is centrifuged at 600 g for 10 minutes. The supernatant fractions are combined. The pellets are discarded. This washing contributes not only to the yield of the final mitochondrial preparation, but also to its integrity, apparently by permitting the recovery of the larger mitochondria. For the isolation of kidney, the kidney capsule is removed by gently squeezing the kidney through the thumb and forefinger. The kidney is then cut sagittally. The medullary portion is removed and discarded. Mitochondria are then prepared from the cortex following the method described for liver, with the exception that the mitochondrial pellet need be washed only once. Method for testing the quality of mitochondria is also discusses in the chapter.

Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds

Spectacular fossils from the Early Cretaceous Jehol Group of northeastern China have greatly expanded our knowledge of the diversity and palaeobiology of dinosaurs and early birds, and contributed to our understanding of the origin of birds, of flight, and of feathers. Pennaceous (vaned) feathers and integumentary filaments are preserved in birds and non-avian theropod dinosaurs, but little is known of their microstructure. Here we report that melanosomes (colour-bearing organelles) are not only preserved in the pennaceous feathers of early birds, but also in an identical manner in integumentary filaments of non-avian dinosaurs, thus refuting recent claims that the filaments are partially decayed dermal collagen fibres. Examples of both eumelanosomes and phaeomelanosomes have been identified, and they are often preserved in life position within the structure of partially degraded feathers and filaments. Furthermore, the data here provide empirical evidence for reconstructing the colours and colour patterning of these extinct birds and theropod dinosaurs: for example, the dark-coloured stripes on the tail of the theropod dinosaur Sinosauropteryx can reasonably be inferred to have exhibited chestnut to reddish-brown tones.

Light element geochemistry of the Chelyabinsk meteorite

The spectacular arrival of a huge meteorite in central Siberia on February 15th 2013 was the largest event of its kind for more than a hundred years. Oxygen isotope analysis reveals the object involved was an ordinary chondrite of type LL. Petrological examination of the material analysed shows two main lithologies, metamorphic grade 5, were present both having veins of shock produced glass. All three types of material were investigated for carbon, nitrogen and noble gas content and isotopic compositions. The relatively low abundance of carbon and nitrogen indicate that Chelyabinsk is uncontaminated by comparison with other samples in meteorite collections so that indigenous components may be recognized. All the samples studied contained minimal amounts of cosmogenic and primordial noble gases, evidence that the pre-atmospheric size of the object was large, greater than two metres in diameter and that the explosion and break-up was accompanied by catastrophic degassing. The implications for other major meteorite falls and the Tunguska event are discussed.

Fourier transform infrared spectral detection of life in polar subsurface environments and its application to Mars exploration

Cryptoendolithic lichen communities of the Dry Valleys, Antarctica, survive in an extremely inhospitable environment, finding refuge in microscopic niches where conditions suitable for life exist. Such “within-rock” communities may have evolved on Mars when conditions for life on the surface deteriorated to such an extent that they could no longer survive. Fourier transform infrared spectroscopy of unprepared whole-rock Antarctic Beacon sandstones was used to vertically profile molecular vibrations of fatty acids, proteins, and carboxylic acids created by endolithic communities. Spectral biosignatures were found localized to lichen-rich areas and were absent in crustal regions and the bulk rock substrate. These cryptoendolithic profiles will aid similar spectroscopic investigations of organic biosignatures during future Martian subsurface studies and will help in the identification of similar communities in other localities across the Earth.

UV-Vis spectroscopy of stardust

NASAs Stardust mission flew through the coma of comet Wild 2 in January 2004, capturing dust grains as it did so. The grains were returned safely to Earth in January 2006, and are in the process of being distributed to investigators. As members of the Spectroscopy Preliminary Examination Team, we are preparing to analyse Stardust grains. Our contribution is to measure the spectrum of the grains between 200 nm (in the near ultraviolet) and 800 nm (near infrared). The purpose of the measurement is to provide an additional technique for characterizing the grains, one that is complementary to other spectroscopic techniques and one that produces results that can be matched directly with spectra acquired remotely (with telescope or spacecraft instrumentation). As part of the preparation for analysis of Stardust materials, we are producing a database of spectra from appropriate minerals, and are honing the technique through analysis of primitive meteorites.