bluuebunny/crossref_metadata_2025 huggingface dataset:
Agricultural Education And Agricultural Communications: Striking A Proper Balance In The Academy
Authors: Tucker Mark , Whaley Sherrie R. , Cano Jamie
Published: December 2010

From its beginnings in the early 1800s, the profession of agricultural communications was born out of the practical need to share important farm and home information with isolated rural audiences. Some 200 years later, agricultural communications has evolved into a diverse industry responsible for developing and disseminating news and marketing information related to food, agricultural, and environmental systems. Professional preparation for such careers is often provided through academic programs that are housed in departments of agricultural education. This administrative arrangement provides both benefits and challenges to the future development of agricultural communications programs, which need to strike important balances in teaching, outreach, and research programs and in collaborative relationships within and outside of the academy. The potential for success is greatly enhanced if agricultural communications development strategies are coordinated with agricultural education to build synergies between the programs while maintaining unique strengths. This philosophical paper uses elements of the sociology of education to address some of the benefits and challenges posed by agricultural communications' close relationships with private industry and other academic departments, including agricultural education. The paper concludes with a list of implications and courses of action recommended for discussion by academicians in the two disciplines.
Problems In Recruiting Students Into Agricultural Education Programs: A Delphi Study Of Agriculture Teacher Perceptions
Authors: Dyer James E. , Breja Lisa M.
Published: December 2010

This national study used the Delphi technique to identify problems that secondary agriculture teachers experience in recruiting students in high school agriculture programs. The study used a series of four mailed questionnaires. The first round of the study used a questionnaire with an open-ended question to facilitate the generation of a wide array of response categories. In round two respondents were asked to rate the 28 problems identified in round one on a Likert-type scale and to make changes in the items as necessary. In rounds three and four respondents were sent the results from the previous round and asked to provide a dichotomous indication of whether or not they agreed or disagreed with each of the revised items. Consensus was reached in the fourth round. The major problems identified by the Delphi technique in the successful recruitment of students into agriculture programs were: scheduling difficulties, finding time to recruit, student involvement in other activities, access to students, competition from other programs, lack of guidance counselor support, increased graduation requirements, image of agriculture, lack of interest in agriculture, and block scheduling.
PRACTICES IN STUDENT EVALUATION OF DISTANCE EDUCATION COURSES AMONG LAND GRANT INSTITUTIONS
Authors: Roberts T. Grady , Irani Tracy , Lundy Lisa K. , Telg Ricky
Published: December 2010

Student attitudes are one of the most important factors when assessing the quality of a distance education program (Keegan, 1990). When examining the research base, a few studies were found that examined the use of student attitudes in evaluating distance education (Biner, 1993; Cheung, 1998). However, sufficient research does not exist to develop a broader picture of the use of student attitudes, particularly when examining agriculturally related institutions. The purpose of this case study was to develop a picture of how instruments that assess student attitudes are used in the distance education evaluation practices of higher education institutions that deliver agriculturally related content. When examining the institutions in this case study, most are delivering distance education to both undergraduate and graduate students. Most of the institutions are using course management software and video conferencing for delivering instruction. Instructors are the most common focus of evaluations, closely followed by course organization and delivery. The most common method for developing a distance education evaluation instrument was to make a few revisions to the on-campus instrument already utilized at each institution.
IDENTIFYING SOURCES OF MOTIVATION OF ADULT RURAL WORKERS
Authors: Barbuto John E. , Trout Shirley K. , Brown Lance L.
Published: December 2010

A meta-theory of motivation is described and used to establish norms among farm cooperative employees and managers in Nebraska. One hundred eighty six farm cooperative employees and managers were administered the Motivation Sources Inventory (MSI) and the five sources of work motivation–intrinsic process, instrumental, self-concept external, self-concept internal, and goal internalization– were examined. Results demonstrate a high proportion of self-concept internal work motivation among rural workers. The other four sources were evenly distributed across the sample population. This baseline study implies that employers, supervisors and educators may engage the interest and involvement of rural workers most effectively when they incorporate influence attempts that appeal to workers’ internally derived standards and sense of the ideal self. Limitations and further implications for education, practice and future research are discussed.
AGRICULTURE TEACHER EDUCATION PROGRAMS: A SYNTHESIS OF THE LITERATURE
Authors: Myers Brian E. , Dyer James E.
Published: December 2010

The role of teacher education programs and the demand placed upon those programs is changing. This study sought to synthesize research related to pre-service agricultural teacher education programs in the following areas: (1) demographics of teacher educators, (2) demographics of teacher education programs, (3) responsibilities of teacher education programs, (4) student selection, (5) preservice curriculum, (6) teacher education program models, and (7) field experiences. After a review of the literature in these areas, deficiencies in the current literature base were identified.
FACTORS EXPLAINING JOB SATISFACTION AMONG FACULTY
Authors: Castillo Jaime X. , Cano Jamie
Published: December 2010

The purpose of this descriptive-correlational study was to describe the amount of variance in faculty member’s overall level of job satisfaction explained by Herzberg, Mausner, and Snyderman’s (1959) job motivator and hygiene factors. Additionally, the study sought to investigate the suitability of a one-item versus a multi-item measure of overall job satisfaction. The faculty were generally satisfied with their jobs. However, female faculty members were less satisfied than male faculty members. The factor “work itself” was the most motivating aspect for faculty. The least motivating aspect was “working conditions.” The demographic characteristics were negligibly related to overall job satisfaction. All of the job motivator and hygiene factors were moderately or substantially related to overall job satisfaction. The factors “recognition,” “supervision,” and “relationships” explained the variability among faculty members’ overall level of job satisfaction. The one-item measure of overall job satisfaction was not different from a multi-item measure of overall job satisfaction.
SUPERVISORY PRACTICES USED BY TEACHER EDUCATORS IN AGRICULTURE: A COMPARISON OF DOCTORAL/RESEARCH EXTENSIVE AND RESEARCH NON-EXTENSIVE INSTITUTIONS
Authors: Fritz Carrie , Miller Greg
Published: December 2010

The purpose of this study was to compare student teacher supervision among doctoral/research extensive and research non-extensive institutions. Results of this census study provide benchmark data on supervisory practices followed by teacher educators in doctoral/research extensive and research non-extensive institutions. The doctoral/research extensive (N=111) and research non-extensive (N=34) teacher educators who participated in the study were predominantly male and most had received formal training on supervision. In addition, these teacher educators devoted, on average, 19% of their academic appointments to supervision, conducted three on-site visits lasting approximately four to five hours, and had served as cooperating teachers for an average of two student teachers. On average, teacher educators from doctoral/research extensive institutions had been university supervisors for 14 years and research non-extensive teacher educators had been university supervisors for 12.5 years. Based on the Supervisory Options for Instructional Leaders (SOIL) Model, respondents from doctoral/research extensive and research non-extensive institutions used components of clinical supervision to a greater extent than they used contextual or differentiated supervision. The most frequently used level of the SOIL Model utilized by teacher educators in doctoral/research extensive institutions was the structured level; however, the moderately structured level was the most frequently utilized by teacher educators in research non-extensive institutions.
RELATIONSHIPS BETWEEN SELECTED DEMOGRAPHIC CHARACTERISTICS AND THE QUALITY OF LIFE OF ADOLESCENTS IN A RURAL WEST TEXAS COMMUNITY
Authors: Smith James H. , Kistler Mark , Williams Kamy , Edmiston Will , Baker Matt
Published: December 2010

Agricultural educators have long had an interest in the viability of rural schools. At least part of this interest can be attributed to the large number of secondary programs located in rural school districts. In this study, the researchers examined the relationships between a composite quality of life measure, perceived control over one’s quality of life, and perceived opportunities for the improvement in one’s quality of life and students’ gender, family socioeconomic status, and number of children and adults residing in the household. The literature indicates that quality of life is associated with various student performance indicators. Findings showed as family socioeconomic status increased, overall quality of life, control, and opportunities also increased. The additional demographic variables included in the study did not have a consistent influence upon the students’ quality of life as measured by the three indicators. In formulating hypotheses, the researchers treated the three components of quality of life as a "bundle" in relation to the ethnicity, livelihood, and household composition variables of interest. If anything, the data have indicated that there is a great deal of variability in the three components based upon these measured variables.
Economic Impact Of Supervised Agricultural Experience In Iowa: A Trend Study
Authors: Retallick Michael S. , Martin Robert A.
Published: December 2010

The focus of this article is on the economic impact of Supervised Agricultural Experience (SAE) programs in Iowa using longitudinal data collected from 1991 to 2001. In order to accomplish the purpose of the study, student net income growth, growth of SAE program hours, SAE income per student and per program, and return on investment using tax dollars invested per student-derived income were calculated. The results of this study show that there is a substantial economic impact related to SAE consistent over the entire 11-year period of the study. The total value of SAE income peaked in 2000 with over $20.9 million dollars and grew at an annualized rate of 6.05% from 1991 to 2001. Unpaid SAE program hours grew considerably more annually (20.06%) than paid SAE hours (9.72%). Over the 11-year study, students with a SAE earned $1,443 on average, whereas each agricultural education program earned $55,984. The return on investment ratio using tax dollars invested per student-derived income through SAE was positive each year of the study. Students earn more money through SAE programs than school districts invest in salaries and travel for agricultural education programs.
The Influence Of Learning Styles On Student Attitudes And Achievement When An Illustrated Web Lecture Is Used In An Online Learning Environment
Authors: Roberts T. Grady , Dyer James E.
Published: December 2010

The technological capabilities of an online-learning environment allow an instructor to make an online class better than a face-to-face class by providing students with learning activities that are individualized to meet their needs and characteristics. One possible learning activity is an illustrated web lecture, which consists of a text-based presentation, such as PowerPoint, with an audio recording of the instructor presenting the lecture. However, a deficiency exists in the research that identifies the student characteristics, such as motivation, self-efficacy, and critical thinking dispositions, which influence student achievement and attitudes when an illustrated web lecture is used. This study sought to fill that void. Results indicated that motivation and computer proficiency tend to influence attitudes and that motivation and prior knowledge influence achievement. It was concluded that when an illustrated web lecture is used to deliver content, students with higher levels of motivation tend to exhibit higher achievement and more favorable attitudes.
The Relationship Of Self-Efficacy, Motivation, And Critical Thinking Disposition To Achievement And Attitudes When An Illustrated Web Lecture Is Used In An Online Learning Environment
Authors: Roberts T. Grady , Dyer James E.
Published: December 2010

The technological capabilities of an online-learning environment allow an instructor to make an online class better than a face-to-face class by providing students with learning activities that are individualized to meet their needs and characteristics. One possible learning activity is an illustrated web lecture, which consists of a text-based presentation, such as PowerPoint, with an audio recording of the instructor presenting the lecture. However, a deficiency exists in the research that identifies the student characteristics, such as motivation, self-efficacy, and critical thinking dispositions, which influence student achievement and attitudes when an illustrated web lecture is used. This study sought to fill that void. Results indicated that motivation and computer proficiency tend to influence attitudes and that motivation and prior knowledge influence achievement. It was concluded that when an illustrated web lecture is used to deliver content, students with higher levels of motivation tend to exhibit higher achievement and more favorable attitudes.
A Document Analysis Of The Pedagogical Knowledge Espoused In Agriculture Teaching Methods Courses
Authors: Ball Anna L. , Knobloch Neil A.
Published: December 2010

The purpose of this study was to examine pedagogical knowledge espoused in teaching methods courses in agricultural education. The population was a census of 64 agricultural teacher educators nationwide who taught a teaching methods course during the 2002-03 academic year. The researchers utilized a content document analysis method (Hodder, 2000) of teaching methods course syllabi to identify the required course readings, assignments, and teaching methods taught by teacher educators. The most frequently required reading resource was Newcomb, McCracken, and Warmbrod's (1986, 1993), Methods of Teaching Agriculture. One-fourth of the teaching methods teacher educators required this text. Nearly one in seven educators required a teaching methods text outside of agricultural education. Teacher educators had a wide range of the types of assignments and amount of work required in their teaching methods courses. Teacher educators spent an average of 21% of the course time teaching methods. The problem-solving approach to teaching was the most widely espoused teaching method in agricultural education course syllabi. The predominant number of teaching methods taught appeared to be directly from Newcomb et al.'s book. Regardless of the teaching method listed in the syllabi, teacher educators spent a low percentage of course time on teaching methods.
Preparation Of Pre-Service Teachers In Agricultural Mehanics
Authors: Burris Scott , Robinson J. Shane , Terry Jr.
Published: December 2010

Teacher education programs face a myriad of challenges in preparing secondary agricultural education teachers. One challenge is providing preparation in technical content areas including agricultural mechanics. The purpose of this study was to determine the level of preparedness of agriculture teacher education program graduates in the area of agricultural mechanics. The target population for the study was certifying institutions for agriculturaleducation teachers in the United States. Data were collected with a mailed questionnaire sent in the fall of 2003. A total of 69 completed surveys were returned for a response rate of 78.4%. More than 90% of respondents indicated that six of the nine content areas were included in their state's secondary curriculum. Respondents identified the level of importance as "important" for each of nine competency groupings. Respondents identified the level of preparation for hand/power tools as "prepared." The remaining eight competency groupings were rated as "somewhat prepared." More than 97% of respondents indicated that some agricultural mechanics credits were required for program completion. The average number of credits required for program completion was 9.13. A majority (58%) of institutions indicated that at least one required course was taught within the department housing the teacher preparation program.
A Description Of The Characteristics Attributed To Students' Decisions To Teach Agriscience
Authors: Park Travis D. , Rudd Rick
Published: December 2010

A major issue facing agricultural education is recruiting qualified young teachers to theprofession. Attempts have been made to recruit new teachers by offering scholarship incentives, highlighting teachers at the National FFA Convention, and producing recruitment brochures. This Delphi study attempts to answer questions about how current agriscience teachers encourage their students to pursue careers in teaching. Respondents were teachers (n=11), stratified across six different southern states, who prolifically produced agricultural education students and future teachers. Findings indicated that teachers who serve as role models, build quality programs, and refrain from disparaging remarks and attitudes about the profession encourage students. Students may be enticed to teach if teachers demonstrate high standards, lead in the school and community, and take an interest in all aspects of a student's life. The research produced five constructs for recruitment of future teachers: encouragement, modeling, career counseling and awareness, program quality, and teacher effectiveness. The most influential constructs were determined to be encouragement and program quality. Career awareness and counseling was the least influential construct.
Comparative Assessment Of Student Agricultural Literacy In Selected Agriculture In The Classroom Programs
Authors: Pense Seburn L. , Leising James G. , Portillo Matthew T. , Igo Carl G.
Published: December 2010

The purpose of this quasi-experimental study was to assess change in student agricultural knowledge after implementing Agriculture in the Classroom (AITC) programs and to identify strengths and weaknesses of student knowledge according to the five thematic areas of the Food and Fiber Systems Literacy (FFSL) Framework. The experimental group was comprised of selected classrooms (K-6) with AITC trained teachers in Arizona, Montana, Oklahoma and Utah. The control group was comprised of selected classrooms (K-6) in the same four states with teachers who had no exposure to AITC. Pre-test and posttest mean score comparisons by grade groupings and in the five thematic areas of the FFSL Framework resulted in greater agricultural knowledge gains in all four grade groupings by the AITC treatment group over the control group. The study concluded that AITC training of teachers made a positive difference in student acquisition of knowledge about agriculture.
Laboratory investigations of the impact of mineral dust aerosol on cold cloud formation
Authors: Koehler K. A. , Kreidenweis S. M. , DeMott P. J. , Petters M. D. , Prenni A. J. , Möhler O.
Published: December 2010

Abstract. Dust particles represent a dominant source of particulate matter (by mass) to the atmosphere, and their emission from some source regions has been shown to be transported on regional and hemispherical scales. Dust particles' potential to interact with water vapor in the atmosphere can lead to important radiative impacts on the climate system, both direct and indirect. We have investigated this interaction for several types of dust aerosol, collected from the Southwestern United States and the Saharan region. A continuous flow diffusion chamber was operated to measure the ice nucleation ability of the dust particles in the temperature range of relevance to cirrus and mixed-phase clouds (−65
Source identification and budget analysis on elevated levels of formaldehyde within the ship plumes: a ship-plume photochemical/dynamic model analysis
Authors: Song C. H. , Kim H. S. , von Glasow R. , Brimblecombe P. , Kim J. , Park R. J. , Woo J. H. , Kim Y. H.
Published: December 2010

Abstract. Elevated levels of formaldehyde (HCHO) along the ship corridors have been observed by satellite sensors, such as ESA/ERS-2 GOME (Global Ozone Monitoring Experiment), and were also simulated by global 3-D chemistry-transport models. In this study, three likely sources of the elevated HCHO levels in the ship plumes as well as their contributions to the elevated HCHO levels (budget) were investigated using a newly-developed ship-plume photochemical/dynamic model: (1) primary HCHO emission from ships; (2) secondary HCHO production via the atmospheric oxidation of non-methane volatile organic compounds (NMVOCs) emitted from ships; and (3) atmospheric oxidation of CH4 within the ship plumes. For this ship-plume modelling study, the ITCT 2K2 (Intercontinental Transport and Chemical Transformation 2002) ship-plume experiment, which was carried out about 100 km off the coast of California on 8 May 2002 (11:00 local standard time), was chosen as a base study case because it is the best defined in terms of (1) meteorological data, (2) in-plume chemical composition, and (3) background chemical composition. From multiple ship-plume model simulations for the ITCT 2K2 ship-plume experiment case, CH4 oxidation by elevated levels of in-plume OH radicals was found to be the main factor responsible for the elevated levels of HCHO in the ITCT 2K2 ship-plume. More than ~88% of the HCHO for the ITCT 2K2 ship-plume is produced by this atmospheric chemical process, except in the areas close to the ship stacks where the main source of the elevated HCHO levels would be primary HCHO from the ships (due to the deactivation of CH4 oxidation from the depletion of in-plume OH radicals). Because of active CH4 oxidation by OH radicals, the instantaneous chemical lifetime of CH4 (τCH4) decreased to ~0.45 yr inside the ship plume, which is in contrast to τCH4 of ~1.1 yr in the background (up to ~41% decrease) for the ITCT 2K2 ship-plume case. A variety of likely ship-plume situations at three different latitudinal locations within the global ship corridors was also studied to determine the enhancements in the HCHO levels in the marine boundary layer (MBL) influenced by ship emissions. It was found that the ship-plume HCHO levels could be 19.9–424.9 pptv higher than the background HCHO levels depending on the latitudinal locations of the ship plumes (i.e., intensity of solar radiation and temperature), MBL stability and NOx emission rates. On the other hand, NMVOC emissions from ships were not found to be a primary source of photochemical HCHO production inside ship plumes due to their rapid and individual dilution. However, the diluted NMVOCs would contribute to the HCHO productions in the background air.
Chemical ionization mass spectrometry (CIMS) may not measure all gas-phase sulfuric acid if base molecules are present
Authors: Kurtén T. , Petäjä T. , Smith J. , Ortega I. K. , Sipilä M. , Junninen H. , Ehn M. , Vehkamäki H. , Mauldin L. , Worsnop D. R. , Kulmala M.
Published: December 2010

Abstract. The state-of-the art method for measuring atmospheric gas-phase sulfuric acid is chemical ionization mass spectrometry (CIMS) based on nitrate reagent ions. Using computed proton affinities and reaction thermodynamics for the relevant charging reactions, we show that in the presence of strong bases such as amines, which tend to cluster with the sulfuric acid molecules, a significant fraction of the total gas-phase sulfuric acid may not be measured by a CIMS instrument. If this is the case, this effect has to be taken into account in the interpretation of atmospheric sulfuric acid measurement data, as well as in intercomparison of different CIMS instruments, which likely have different susceptibilities to amine-sulfuric acid clustering.
Response of the Black Sea methane budget to massive short-term submarine inputs of methane
Authors: Schmale O. , Haeckel M. , McGinnis D. F.
Published: December 2010

Abstract. A steady state box model was developed to estimate the methane input into the Black Sea water column at various water depths. Our model results reveal a total input of methane of 4.7 Tg yr−1. The model predicts that the input of methane is largest at water depths between 600 and 700 m (7% of the total input), suggesting that the dissociation of methane gas hydrates at water depths equivalent to their upper stability limit may represent an important source of methane into the water column. In addition we discuss the effects of massive short-term methane inputs (e.g. through eruptions of deep-water mud volcanoes or submarine landslides at intermediate water depths) on the water column methane distribution and the resulting methane emission to the atmosphere. Our non-steady state simulations predict that these inputs will be effectively buffered by intense microbial methane consumption and that the upward flux of methane is strongly hampered by the pronounced density stratification of the Black Sea water column. For instance, an assumed input of methane of 179 Tg CH4 d−1 (equivalent to the amount of methane released by 1000 mud volcano eruptions) at a water depth of 700 m will only marginally influence the sea/air methane flux increasing it by only 3%.
Parameterising the grounding line in flow-line ice sheet models
Authors: Gladstone R. M. , Payne A. J. , Cornford S. L.
Published: December 2010

Abstract. Realistic predictions of the behaviour of marine ice sheets require that models are able to robustly simulate grounding line migration. Fixed-grid ice sheet models have been shown to exhibit inconsistent and hence unreliable grounding line migration, except at very high resolution not yet achievable in whole ice sheet simulations. In this study we present several different approaches to parameterising the grounding line. These are distinguished by choices regarding the ice thickness profile from the last grounded to the first floating grid point, and how this profile impacts the gravitational driving stress and basal drag. We demonstrate that the most obvious choice of thickness parameterisation, linear interpolation from the last grounded to the first floating grid point, is not the most effective. We show that use of a grounding line parameterisation greatly improves performance, and that choice of a better grounding line parameterisation over a simpler one can bring further improvements, in terms of both accuracy and self consistent behaviour, comparable to increasing the grid resolution by factor two (i.e. doubling the number of grid points). The approach presented here to parameterising the grounding line does not completely solve the grounding line problem, however it reduces the resolution required. The parameterisations are presented in the context of a one dimensional "shelfy-stream" flow-line model, but could be extended to cope with more than one dimension and other model formulations.
Peptidylglycine α‐Hydroxylating Monooxygenase (PHM)
Authors: Rudzka Katarzyna , Chufán Eduardo E , Eipper Betty , Mains Richard , Amzel Mario L
Published: December 2010

Numerous peptides function as hormones, neurotransmitters, and growth factors. Enzymatic α‐amidation is a biologically important posttranslational modification of the C‐terminus of many of these peptides. This modification alters the biological properties and enhances the stability of the peptides toward digestion by carboxypeptidases. Peptidylglycine α‐hydroxylating monooxygenase (PHM) is an ascorbate and copper‐dependent catalytic domain of an α‐amidating enzyme (peptidylglycine α‐amidating monooxygenase, PAM) that catalyzes the stereospecific hydroxylation of an α‐carbon of a terminal glycine residue, the first step in the amidation reaction. This reaction is followed by cleavage of the glycine N Cα bond, which is carried out by the second PAM catalytic domain, peptidyl‐α‐hydroxyglycine α‐amidating lyase (PAL). Detailed structural studies of PHM revealed that its catalytic core binds two copper ions that support the oxygenation reaction by cycling through Cu(II)/Cu(I) oxidation states. These two Cu ions (CuHand CuM) are located 11 Å apart and are separated by a solvent‐accessible cleft. The monooxygenation reaction requires the two‐electron activation of molecular oxygen, which is achieved by the binding of O2to a single Cu(I) center (CuM). Formation of this complex is dependent upon the presence of a peptidylglycine substrate and a reducing agent (ascorbate). Since the resting state of the enzyme contains two Cu(II) ions, the catalytic reaction requires transfer of two electrons from the reducing agent to the metal centers, and from the reduced copper ions to dioxygen. The reduced oxygen species then carries out the stereospecific hydroxylation of glycine after abstraction of thepro‐Shydrogen from Cα. Although, the structure and function of PHM have been broadly studied, the pathway of its electron transfer, the nature of the metal‐oxygen species, and details of the mechanism are still being investigated.
Superoxide Reductase
Authors: Nivière Vincent , Bonnot Florence , Bourgeois Dominique
Published: December 2010

Superoxide reductase (SOR) is a small bacterial metalloprotein, which is present in the cytoplasm of some anaerobic or microaerophilic microorganisms. SOR is involved in the detoxification of the superoxide radical and catalyzes its one‐electron reduction into hydrogen peroxide. Three different classes of SOR have been identified and structurally characterized. They all contain a similar active site, which consists of an unusual nonheme iron center, coordinated in a square‐pyramidal geometry to four nitrogens from four histidine side chains in the equatorial plane and the sulfur of one cysteine residue along the fifth axial position. In the reduced state, the sixth axial coordinating site of the iron is vacant, suggesting the most obvious site for initial binding of the superoxide substrate. The reaction mechanism of SOR has been studied by pulse radiolysis. SOR reacts specifically at a nearly diffusion‐controlled rate with O
2
•−
, generating H
2
O
2
and the oxidized Fe
3+
active site. Reaction intermediates have been observed and proposed to be Fe
3+
‐(hydro)peroxo species, resulting from the fast electron transfer from the ferrous iron to the superoxide anion and from protonation step. Formation of Fe
3+
‐(hydro)peroxo intermediate species in the active site of SOR has been supported by resonance Raman spectroscopy and X‐ray structures of iron(III) peroxide species in the SOR from
Desulfoarculus baarsii
.
Axon Growth
Authors: Toro Carla , Sousa Catia , Tannahill David
Published: December 2010

During embryogenesis, the construction of the nervous system requires that nerve cells connect very precisely to each other and to peripheral tissues. Establishment of these connections involves the growth and extension of long thin processes, known as axons, from the main body of the cell. The tip of this growing axon displays a highly specialised and dynamic structure, called the growth cone. Growth cone sense information presented to it in the embryonic environment and respond by steering axon growth towards the correct targets.

Key Concepts:

The growth cones of growing nerves control axon outgrowth and direction.

Growth cones sense a variety of signals in the environment that initiate a variety of intracellular signalling events.

Growth signals act through the Rho‐GTPase signalling pathways to regulate microtublule dynamics that in turn influences the actinomyosin cytoskeleton.

Once development is complete, axon growth may continue in discrete neurogenic regions of the brain and also following nerve injury.

Intracellular second messengers such as calcium are important in mediating the response of growth cones to attractive and repulsive cues.
Cell Macromolecules
Authors: Bray Dennis
Published: December 2010

The distinctive properties of living organisms arise from very large molecules called macromolecules, which may contain anything from hundreds to many billions of atoms. Macromolecules are polymers made in the cell by linking small chemical subunits together in a specific sequence. Nucleic acids –
deoxyribonucleic acid
and
ribonucleic acid
– are polymers of nucleotide bases and their principle function is to store and transmit hereditary information encoded in the sequence of subunits. Proteins are chains of amino acids that fold up into distinctive shapes and thereby acquire distinctive chemical properties, they are the principal building blocks of the cell and also responsible for activities such as enzyme catalysis, the synthesis of molecules and movements. Nucleic acids, proteins and other macromolecules such as polysaccharides interact with each other and with small molecules through weak chemical bonds. These allow specific molecular recognition to occur and form the basis of information transfer, cell movements, differentiation and the formation of distinctive cells and tissues.

Key Concepts:

Macromolecules are polymers built from subunits in a specific sequence.

Covalent bonds hold a macromolecule together; noncovalent bonds enable it to recognise other molecules.

RNA and DNA carry information in their nucleotide sequence.

Proteins fold into specific shapes and provide the building blocks of the cell.

The function of a protein depends on its ability to interact with and modify other molecules.
Protozoan Ecology
Authors: Anderson O Roger
Published: December 2010

Protozoan ecology is the interaction in space and time of protozoa (flagellates, amoeboid organisms and ciliates) with other living organisms and the physical environment. It encompasses, among other factors, sources of food and energy used to sustain life, food web dynamics, the role of protozoa in maintaining fertility of ecosystems and adaptive strategies for survival in varying habitats. Among the physical environmental (abiotic) factors, temperature, salinity, nutrients and levels of pollutants, when present, are major sources of influence. A complex set of interactions exists among microbial biota, including the role of nutrient regeneration during protozoan predation on bacteria resulting in release of nutrients due to digestion and disruption of the bacteria during feeding. These nutrients in turn are reutilised by algae during photosynthesis. This process of cyclical nutrient uptake by algae and subsequent release by protozoan predation is known as ‘the microbial loop’.

Key Concepts:

Characteristics of the physical environment (including temperature, available nutrients and salinity) set the boundary conditions for the abundance and diversity of protozoa within a given habitat.

Algae and other photosynthetic organisms are primary producers that fix carbon into organic compounds through photosynthesis and thus provide food sources for all other organisms, including protozoa, within a food web.

Heterotrophic (nonphotosynthetic) microorganisms, particularly the protozoa, prey on algae and other microbes, including bacteria, and are consumers within food webs.

A complex set of interactions exist in microbial communities, including predator–prey relationships, that determine the flow of matter and energy through the food webs.

Competition within and among species partially accounts for the abundance and diversity of species in a microbial community.

The stability of microbial communities depends in part on the diversity of species and available resources needed to support life.

Protozoa, as predators and also as prey for larger organisms, are often key members of microbial communities and sustain the flow of energy and matter through food webs, including the regeneration of nutrients through their significant role in the microbial loop.
Plant Quantitative Traits
Authors: Ikram Sobia , Chardon Fabien
Published: December 2010

In plants, most of the phenotypic variations are continuously distributed and could be considered as quantitative traits. The complexity of their genetic control is high because the involved genes are numerous, with usually minor effects and very sensitive to environment. The implicated loci are localised by two basic approaches, linkage mapping and association mapping, based on the use of genetic maps and sophisticated statistical analysis. Linkage mapping leads to the identification of small regions of genome but that could contain still several hundred genes. Identification of gene underlying the quantitative trait loci requires positional cloning or direct tests of promising candidates. Association mapping checks directly the relationship between each polymorphism and phenotypic trait variation in wild populations, but physical linkage and population structure are sources of false positives. Finally, validation that an individual gene is responsible for the quantitative trait needs to be performed by using genetic or functional complementation.

Key Concepts:

Quantitative traits follow continuous, unbroken quasi‐normal distributions whereas qualitative (mendelian) traits are discreetly distributed.

Quantitative traits are controlled by several genes, with small additive, dominant or epistatic effects, and in interaction with the environment.

A quantitative trait loci (QTL) is defined as an area of genome associated with an effect on a quantitative trait.

The combination of alleles at the many genes involved in a quantitative trait leads to constitute the different phenotypes.

QTL mapping relies on statistical linkage analysis among quantitative trait and genetic markers using a population that carries combinations of alleles derived from parental lines.

Association mapping looks for association between a genetic marker and phenotype in unrelated individuals by exploiting historical recombination events and genetic diversity.

Population structure is the presence of hidden subgroups in wild populations that appear because of relatedness and selection with an unequal distribution of alleles.

Physical linkage and population structure are sources of linkage disequilibrium and might influence the genome‐wide association (GWA) mapping by creation of false marker‐trait association.

Positional cloning of QTL involves the identification of closely linked recombination events requiring analysis of a large number of segregating progeny with molecular markers covering the critical region.

Complete genome sequencing has greatly advanced the use of GWA mapping.
HIV
Life Cycle and Inherited Co‐receptors
Authors: Bukrinsky Michael I
Published: December 2010

‘Human immunodeficiency virus’ (HIV) is a

Lentivirus

of the family
Retroviridae
, members of which cause a number of neurological and immunological diseases in humans and animals. HIV is the causative agent of the acquired immune deficiency syndrome (AIDS). The disease is caused by virus‐mediated depletion of CD4+ T lymphocytes, preferentially
CCR5
‐positive memory T cells. Most of these cells localise to mucosal tissue, in particular gut mucosa, and disruption of the gut mucosal barrier is an early feature of HIV infection that determines the pathogenesis of the disease. More than 20 years of intensive studies identified the molecular mechanisms underlying viral replication and disease pathogenesis, and provided the foundation for development of antiviral therapeutics and vaccine. This article provides a brief overview of the HIV life cycle and focuses on receptors that determine viral binding and entry into the target cells.

Key Concepts:

Virus–cell interaction is initiated by interaction between gp120 and target cell receptors.

HIV preferentially targets memory CD4+ T cells which localise to mucosal lymphoid tissue, in particular the gut mucosa.

HIV replication includes a number of distinct steps: virus–cell fusion and viral entry; viral uncoating; viral reverse transcription and formation of the pre‐integration complex (PIC); PIC nuclear entry and integration; viral transcription and translation; viral assembly and release of nascent virions; viral.

Characterisation of the molecular mechanisms underlying HIV replication and interaction with the target cells provides an opportunity to develop anti‐HIV therapeutics and vaccine.
Endocytic Organelles: Methods for Preparation and Analysis
Authors: Guimaraes de Araujo Mariana Eca , Fialka Irene , Huber Lukas A
Published: December 2010

Endocytic organelles can be prepared using a variety of techniques. Methods include the homogenisation of cells, the isolation of endosomes by density centrifugation, electromigratory techniques, immunoisolation and fluorescence‐activated organelle sorting (FAOS). The integration of these biochemical techniques with large‐scale proteomics has lead to the rapid expansion of the organelle proteomes characterised. Unfortunately, several limitations have been uncovered. First, the isolation of pure endosomal compartments is rarely achieved. Second, the constant flux of proteins from and to a specific organelle leads to variations in proteome composition that are often time‐ and signalling‐dependent. Innovative approaches such as protein correlation profiling (PCP) and localisation of organelles by isotype tagging (LOPIT) may, in the near future, bring us closer to our aim: the generation of a detailed and reliable organelle proteome chart that accounts for time‐ and signalling‐dependent fluxes as well as variations in the posttranslational modifications (PTMs) observed.

Key Concepts:

The quality of subcellular organelle purification depends to a great extent on the homogenisation procedure.

Upon homogenisation, several methods can be employed to enrich the organelle of choice (density centrifugation, electromigratory techniques, immunoisolation and FAOS).

Subcellular organelle proteomes have been uncovered by the powerful combination of cell biology/biochemistry techniques with large‐scale proteomics.

Innovative methodologies are being established to overcome some of the caveats observed on the initial organelle proteome studies.

Future organelle proteome studies will focus on the dynamics of protein association with organelles (time and signalling specificity). They will also focus on posttranslational modifications and their direct impact on protein function.
Cell Staining: Fluorescent Labelling of the Golgi Apparatus
Authors: Dejgaard Selma Y , Dejgaard Kurt , Presley John F
Published: December 2010

Immunofluorescence has been the primary method for labelling the Golgi apparatus for light microscopic observation in fixed cells. The Golgi apparatus was initially labelled in living cells by using that the fluorescent ceramide analogue
N
‐6[7‐nitro‐2,1,3‐benzoxadiazol‐4‐yl] aminocaproyl sphingosine or by microinjection of fluorescently conjugated antibodies to exposed Golgi epitopes. With the common availability of the green fluorescent protein (GFP) and advanced fluorescence microscopes including confocal microscopes, imaging of the Golgi apparatus in living cells is now a major experimental approach. Time‐lapse imaging of living cells has also been combined with photobleach techniques in order to study the dynamics of transient protein association with the Golgi apparatus. Similar approaches have been used to study the dynamics of the cargo transport through the exocytic pathway.

Key Concepts:

Immunofluorescence can be used to visualise proteins in the Golgi apparatus or its subdomains.

Live‐cell visualisation of the Golgi apparatus is possible with GFP‐tagged proteins.

Photobleaching and photoactivation techniques permit visualisation of protein dynamics and flux through the Golgi apparatus in living cells.
Nucleolus: Structure and Function
Authors: Olson Mark OJ
Published: December 2010

The nucleolus is the nuclear subdomain that assembles ribosomal subunits in eukaryotic cells. The nucleolar organiser regions of chromosomes, which contain the genes for pre‐ribosomal
ribonucleic acid
(rRNA), serve as the foundation for nucleolar structure. The nucleolus disassembles at the beginning of mitosis, its components disperse in various parts of the cell and reassembly occurs during telophase and early G1 phase. Ribosome assembly begins with transcription of pre‐rRNA. During transcription ribosomal and nonribosomal proteins attach to the RNA. Subsequently, there is modification and cleavage of pre‐rRNA and incorporation of more ribosomal proteins and 5S rRNA into maturing pre‐ribosomal complexes. The nucleolus also contains proteins and RNAs that are not related to ribosome assembly and a number of new functions for the nucleolus have been identified. These include assembly of signal recognition particles, sensing cellular stress and transport of human immunodeficiency virus 1 (HIV‐1) messenger RNA.

Key Concepts:

The nucleolus, whose primary function is to assemble ribosomes, is the largest structure in the cell nucleus.

The nucleolus organiser regions of chromosomes, which contain the genes for pre‐rRNA, are the foundation for the nucleolus.

All active nucleoli contain at least two ultrastructural components, the nucleolar dense fibrillar component representing early pre‐ribosomal complexes and the granular component containing more mature pre‐ribosomal particles.

Most nucleoli in higher eukaryotes also contain fibrillar centres, which are the interphase equivalents of the nucleolus organiser regions.

The nucleolus disassembles at the beginning of mitosis and begins to reassemble in telophase.

Ribosome assembly begins with the transcription of pre‐rRNA by RNA polymerase I.

Ribosomal and nonribosomal proteins and 5S RNA associate with the pre‐rRNA during and after transcription.

The pre‐rRNA is modified and processed into rRNA with the aid of nonribosomal proteins and small nucleolar RNAs.

The nucleolus has numerous other functions including assembly of signal recognition particles, modification of transfer RNAs and sensing cellular stress.