Template polymerization of nucleotide analogues

Recent work on the template-directed reactions of the natural D-nucleotides has made it clear that l-nucleotides and nucleotide-like derivatives of other sugars would strongly inhibit the formation of long oligonucleotides. Consequently, attention is focusing on molecules simpler than nucleotides that might have acted as monomers of an information transfer system. We have begun a general exploration of the template directed reactions of diverse peptide analogues. I will present work by Dr. Taifeng Wu on oxidative oligomerization of phosphorothioates and of Dr. Mary Tohidi on the cyclic polymerization of nucleoside and related cyclic pyrophosphates

The Problem of the "Prebiotic and Never Born Proteins"

It has been argued that the limited set of proteins used by life as we know it could not have arisen by the process of Darwinian selection from all possible proteins. This probabilistic argument has a number of implicit assumptions that may not be warranted. A variety of considerations are presented to show that the number of amino-acid sequences that need have been sampled during the evolution of proteins is far smaller than assumed by the argument.Comment: 14 Pages; International Journal of Astrobiology / FirstView Article / October 2012, pp 1

Improving LGBT Cultural Competence in Senior Nursing Students

LGBT (lesbian, gay, bisexual, transgender) health care is considered a national priority by The Institute of Medicine (IOM, 2011) and HealthyPeople 2020 (2013). The shortage of LGBT culturally competent health care providers is a top contributor to the oppression and discrimination affecting LGBT health (2013). The purpose of the evidence-based practice (EBP) project was to improve the cultural competence of nursing students by improving their knowledge, attitudes, and skills in working with the LBGT population. A multi-method intervention was provided to seniors in a baccalaureate program. The project took place at a private Midwestern university and utilized a pretest/post-test design. The Purnell Model for Cultural Competence provided the framework for this project and the Model for Evidence-Based Practice Change guided implementation. A questionnaire including demographics, knowledge, attitudes, and skills items, was completed by students during a required nursing course. A PowerPoint lecture, a panel discussion with members of the university LGBT group, and an interactive role-play activity between nursing students and LGBT group members was implemented during three 50-minute class periods over one week. The questionnaire was completed again following the intervention. Paired t-tests of the subscales knowledge, attitudes and skills revealed statistically significant improvement of each subscale, indicating improved cultural competence. The knowledge subscale t-test revealed a pretest mean of 4.21 (SD = 1.64) and a post-test mean of 6.81 (SD = 1.12), and a significant increase in knowledge from pretest to post-test (t(51) = -12.717, p =.000). The attitudes t-test found a pretest mean of 13.08 (SD = 3.99), a post-test mean of 11.34 (SD = 3 .17), and a significant decrease in negative attitudes (t(52)=4.86, p=.000). The paired-samples t test for the skills subscale identified a pretest mean of 20.23 (SD = 4.71), a post-test mean of 16.34 (SD = 4.87), and lack of skills significantly decreased, (t(52) = 5.64, p = .000). Maintenance of this intervention at the university would increase LGBT cultural competence of nursing students

Degradation of small simple and large complex lunar craters: Not a simple scale dependence

The crater record of a planetary surface unit is often analyzed by its cumulative size‐frequency distribution (CSFD). Measuring CSFDs involves traditional approaches, such as traditional crater counting (TCC) and buffered crater counting (BCC), as well as geometric corrections, such as nonsparseness correction (NSC) and buffered nonsparseness correction (BNSC). NSC and BNSC consider the effects of geometric crater obliteration on the CSFD. On the Moon, crater obliteration leads to two distinct states in which obtained CSFDs do not match the production CSFD—crater equilibrium and nonsparseness. Crater equilibrium occurs when each new impact erases a preexisting crater of the same size. It is clearly observed on lunar terrains dominated by small simple craters with steep‐sloped production CSFDs, such as Imbrian to Eratosthenian‐era mare units. Nonsparseness, on the other hand, is caused by the geometric overlap of preexisting craters by a new impact, which is also known as “cookie cutting.” Cookie cutting is most clearly observed on lunar terrains dominated by large craters with shallow‐sloped production CSFDs, such as the pre‐Nectarian lunar highlands. We use the Cratered Terrain Evolution Model (CTEM) to simulate the evolution of a pre‐Nectarian surface unit. The model was previously used to simulate the diffusion‐induced equilibrium for small craters of the lunar maria. We find that relative to their size, large craters contribute less to the diffusion of the surrounding landscape than small craters. Thus, a simple scale dependence cannot account for the per‐crater contribution to degradation by small simple and large complex craters

The molecular structure of collagen

This thesis describes the study of the molecular packing and organisation of collagen molecules within a fibril. The first two chapters describe the background to the study. In Chapter 1, a review of the extracellular matrix concentrates on the structure and organisation of type I collagen. Chapter 2 summarises the theory of X-ray diffraction by fibres, and Chapter 3 describes X-ray sources and equipment used in data collection. Data treatments and data extraction methods (such as simulated annealing) are also discussed. Chapters4 and 5 present the results of the study. Chapter 4 describes the determination of the one-dimensional structure of type I collagen to 0.54 nm resolution using X-ray diffraction and isomorphous derivative phase determination. The significance of the electron density map is interpreted in light of the known amino acid sequence, showing possible variations in the nature of the helix pitch. More importantly, the conformations of the intermolecular crosslink forming non-helical telopeptides were determined. Chapter 5 provides a detailed background to the current understanding of the three dimensional packing structure of collagen, and presents the first model-independent phase determined structure of a natural fibre - the lateral packing structure of type I collagen in rat tail tendon. The data extraction methods described in Chapter 3 are employed to calculate an electron density map of anisotropic resolution, from which the 4 crosslink forming telopeptide segments within the quasi-hexagonal packing structure are identified. Conclusions are drawn concerning the nature of order/disorder within collagen fibrils and the validity of the compressed microfibril model of collagen molecular packing and organisation is discussed. Chapter 6 summaries the results and evaluates the success of the study. The potential for development of the techniques and results found for further studies are also discussed

Phosphorylation of Glyceric Acid in Aqueous Solution Using Trimetaphosphate

The phosphorylation of glyceric acid is an interesting prebiotic reaction because it converts a simple, potentially prebiotic organic molecule into phosphate derivatives that are central to carbohydrate metabolism. We find that 0.05 M glyceric acid in the presence of 0.5 M trimetaphosphate in alkaline solution gives a mixture of 2- and 3-phosphoglyceric acids in combined yields of up to 40%

X-Ray Diffraction Detects D-Periodic Location of Native Collagen Crosslinks In Situ and Those Resulting from Non- Enzymatic Glycation

Synchrotron based X-ray diffraction experiments can be highly effective in the study of mammalian connective tissues and related disease. It has been employed here to observe changes in the structure of Extra-Cellular Matrix (ECM), induced in an ex vivo tissue based model of the disease process underlying diabetes. Pathological changes to the structure and organization of the fibrillar collagens within the ECM, such as the formation of non-enzymatic crosslinks in diabetes and normal aging, have been shown to play an important role in the progression of such maladies. However, without direct, quantified and specific knowledge of where in the molecular packing these changes occur, development of therapeutic interventions has been impeded. In vivo, the result of non-enzymatic glycosylation i.e. glycation, is the formation of sugar-mediated crosslinks, aka advanced glycation end-products (AGEs), within the native D-periodic structure of type I collagen. The locations for the formation of these crosslinks have, until now, been inferred from indirect or comparatively low resolution data under conditions likely to induce experimental artifacts. We present here X-ray diffraction derived data, collected from whole hydrated and intact isomorphously derivatized tendons, that indicate the location of both native (existing) and AGE crosslinks in situ of D-periodic fibrillar collagen

Oligonucleotides as probes for studying polymerization reactions in dilute aqueous solution. 2: Polycondensations

We have prepared a (P-32)-labeled oligonucleotide probe carrying a ureido (-NH-CO-NH2) function at its 3'-terminus. This labeled oligomer was used to study polycondensations of urea and formaldehyde and of various phenols and formaldehyde in aqueous solution. The formation of formaldehyde copolymers attached to the amido-function of the probe was monitored by gel electrophoresis. Our results are generally in agreement with those obtained using conventional techniques. Our method is suitable for monitoring potentially prebiotic polycondensation reactions involving formaldehyde

Re-examination of the Population, Stratigraphy, and Sequence of Mercurian Basins: Implications for Mercurys Early Impact History and Comparison with the Moon

Mercury has one of the best preserved impact records in the inner Solar System due to the absence of an atmosphere, but it has much higher rates of surface modification than on the Moon. The earliest geological mapping of the planet revealed a variety of important differences from the Moon, regarding the impact basin (D 300 km) and cratering record, as well as the extensive volcanic plains of Mercury [1-3]. It has been shown [3] that the bombardment history of the terrestrial planets is lunar-like and linked in terms of impactor population(s) and impact rates. Recent studies suggest that Mercury and the Moon had the same early impactor populations based on the similarity of their crater size-frequency distributions (CSFD), however the impact rates on Mercury are higher than on the Moon. Catalogued and characterized the basin population on Mercury using early optical data obtained by the MESSENGER spacecraft and found 46 certain and probable impact basins, as well as 41 tentative