The term mortality is used to describe how many deaths are caused by a given disease in a given population buy ditropan 5mg with amex. Pathogens are transmitted from these sources to susceptible persons either directly (person-to-person) or indirectly via in- ert objects or biological vectors buy ditropan 5 mg free shipping. Control of infectious diseases within a pop- ulace must be supported by effective legislation that regulates mandatory reporting where required order 2.5 mg ditropan visa. Further measures must be implemented to pre- vent exposure, for example isolation, quarantine, disinfection, sterilization, use of insecticides, and dispositional prophylaxis (active and passive immu- nization, chemoprophylaxis). The field covered by this discipline can thus be defined as medical problems involving large collectives. The rule of thumb on infectious diseases is that their characteristic spread depends on the virulence of the pathogen involved, the susceptibility of the threatened host species population, and environmental factors. Transmission, Sources of Infection Transmission Pathogens can be transmitted from a source of infection by direct contact or indirectly. Cattle, pig, goat, Contact with tissues or sheep, (dog) secretions from diseased animals; milk and dairy products Lyme disease Borrelia Wild rodents; Ticks burgdorferi red deer, roe deer Plague Yersinia pestis Rodents Contact with diseased animals; bite of rat flea Q fever Coxiella burnetii Sheep, goat, Dust; possibly milk or cattle dairy products Enteric Salmonella Pig, cattle, Meat, milk, eggs salmonellosis enterica (enteric poultry serovars) Kayser, Medical Microbiology © 2005 Thieme All rights reserved. Bacterial zoonoses Ehrlichiosis; erysipeloid; campylobacteriosis; cat scratch disease; leptospirosis; anthrax; ornithosis; rat-bite fever; rickettsioses (variety of types); tularemia; gastroenteritis caused by Vibrio parahaemolyticus; gastroenteritis caused by Yersinia enterocolitica. Protozoan zoonoses African trypanosomosis (sleeping sickness); American trypanosomosis (Chagas disease); babesiosis; balanti- dosis; cryptosporidosis; giardiosis; leishmaniosis; micro- sporidosis; sarcocystosis; toxoplasmosis. Zoonoses caused Flea infestation; larva migrans externa; mite infestation; by arthropods sand flea infestation. The primary source of infection is defined as the location at which the pathogen is present and reproduces. Sec- ondary sources of infection are inanimate objects, materials, or third per- sons contributing to transmission of pathogens from the primary source to disposed persons. General Epidemiology 31 The Fight against Infectious Diseases 1 Legislation Confronting and preventing infectious diseases can sometimes involve sub- stantial incursions into the private sphere of those involved as well as eco- nomic consequences. For these reasons, such measures must be based on ef- fective disease control legislation. In principle, these laws are similar in most countries, although the details vary. The centerpiece of every disease prevention system is provision for re- porting outbreaks. Basically, reporting is initiated at the periphery (individual patients) and moves toward the center of the system. Concrete countermeasures in the face of an epidemic take the form of pro- phylactic measures aimed at interrupting the chain of infection. Exposure Prophylaxis Exposure prophylaxis begins with isolation of the source of infection, in par- ticular of infected persons, as required for the disease at hand. Quarantine refers to a special form of isolation of healthy first-degree contact persons. The quarantine period is equivalent to the incubation period of the infectious disease in question (see International Health Regulations, www. Further measures of exposure prophylaxis include disinfection and steri- lization, use of insecticides and pesticides, and eradication of animal carriers. In active immunization, the immune system is stimu- lated by administration of vaccines to develop a disease-specific immunity. Re- commended adult immunization schedules by age group and by medical conditions are also available in the National Immunization Program Website mentioned above. The vaccination calendars used in other countries deviate from these proposals in some details. For instance, routine varicella and Kayser, Medical Microbiology © 2005 Thieme All rights reserved. Varicella vaccine is recommended for children who lack a reliable history of chickenpox. The “killed virus vaccine” is recommended in selected regions and for certain high-risk groups. Chil- dren aged –< eight years who are receiving influenza vaccine for the first time should receive two doses separated at least four weeks. To simplify the application of vaccines, licensed combination vaccines may be used whenever any components of the com- bination are indicated and the vaccine’s other components are not contrain- dicated. This vaccination method involves administration of antibodies produced in a different host. In most cases, homologous (human) hyperimmune sera (obtained from convalescent patients or patients with multiple vaccinations) are used. The passive immunity obtained by this method is limited to a few weeks (or months at most). Principles of Sterilization and Disinfection & Sterilization is defined as the killing or removal of all microorganisms and viruses from an object or product. The term asepsis covers all measures aiming to prevent contamination of objects or wounds. A measure of the efficacy of this process is the D value (decimal reduction time), which expresses the time required to reduce the organism count by 90%. The sterilization agents of choice are hot air (1808C, 30 minutes; 1608C,120 minutes) or saturated water vapor (121 8C,15 minutes, 2. Gamma rays or high-energy electrons are used in radiosterilization at a re- commended dose level of 2. Disinfection is usually done with chemical agents, the most important of which are aldehydes (formaldehyde), alcohols, phenols, halogens (I, Cl), and surfactants (detergents). An object that has been subjected to a sterilization process, then packaged so as to be contamination-proof, is considered sterile. Principles of Sterilization and Disinfection 35 Killing of Prions and Thermophilic Archaea 1 The standard sterilization methods used in medical applications (see below) are capable of causing irreversible damage to medically relevant microorganisms such as bacteria, protozoans, fungi, and helminths including worm eggs. Much more extreme processes are required to inactivate prions, such as autoclaving at 1218C for 4. These extreme life forms, along with prions, are not covered by the standard defini- tions of sterilization and sterility. Disinfection is a specifically targeted antimicrobial treatment with the ob- jective of preventing transmission of certain microorganisms. The purpose of the disinfection procedure is to render an object incapable of spreading in- fection. Preservation is a general term for measures taken to prevent microbe- caused spoilage of susceptible products (pharmaceuticals, foods). Decontamination is the removal or count reduction of microorganisms contaminating an object. The objective of aseptic measures and techniques is to prevent microbial contamination of materials or wounds. In antiseptic measures, chemical agents are used to fight pathogens in or on living tissue, for example in a wound. The Kinetics of Pathogen Killing Killing microorganisms with chemical agents or by physical means involves a first-order reaction. This implies that no pathogen-killing method kills off all the microorganisms in the target population all at once and instantaneously. Plotting the killing rate against exposure time in a semilog coordinate system results in a straight-line curve (Fig. Sigmoid and asymptotic killing curves are exceptions to the rule of expo- nential killing rates. The steepness of the killing curves depends on the sen- sitivity of the microorganisms to the agent as well as on the latter’s effective- ness. The survivor/exposure curve drops at a steeper angle when heat is ap- plied, and at a flatter angle with ionizing radiation or chemical disinfectants. Another contributing factor is the number of microorganisms contaminating a product (i. The higher the initial concentration of a bacterial culture, the longer an applied antimicrobial agent will require to achieve the same effect. Time exposed to antimicrobial agent Standard sterilization methods extend beyond killing all microorganisms on the target objects to project a theoretical reduction of risk, i. The D value (decimal reduction time), which expresses the time required to reduce the organism count by 90%, is a handy index for killing effective- ness. The concentration (c) of chemical agents plays a significant role in patho- gen-killing kinetics. The relation between exposure time (t) and c is called the dilution coefficient (n): t Á cn = constant.
She might try to understand why the boy is making this particular statement at this particular time and wonder if he might be attempting to influence her through the comment order 5mg ditropan mastercard. Cognitive psychologists maintain that when we take into consideration how stimuli are evaluated and interpreted discount 5 mg ditropan visa, we understand behavior more deeply discount ditropan 2.5 mg on line. Cognitive psychology remains enormously influential today, and it has guided research in such varied fields as language, problem solving, memory, intelligence, education, human development, social psychology, and psychotherapy. The cognitive revolution has been given even more life over the past decade as the result of recent advances in our ability to see the brain in action using neuroimaging techniques. Neuroimaging is the use of various techniques to provide pictures of the structure and function of the living brain (Ilardi & Feldman,  2001). These images are used to diagnose brain disease and injury, but they also allow researchers to view information processing as it occurs in the brain, because the processing causes the involved area of the brain to increase metabolism and show up on the scan. We have already discussed the use of one neuroimaging technique, functional magnetic resonance Attributed to Charles Stangor Saylor. Social-Cultural Psychology A final school, which takes a higher level of analysis and which has had substantial impact on psychology, can be broadly referred to as the social-cultural approach. The field of social- cultural psychology is the study of how the social situations and the cultures in which people find themselves influence thinking and behavior. Social-cultural psychologists are particularly concerned with how people perceive themselves and others, and how people influence each other’s behavior. For instance, social psychologists have found that we are attracted to others  who are similar to us in terms of attitudes and interests (Byrne, 1969), that we develop our  own beliefs and attitudes by comparing our opinions to those of others (Festinger, 1954), and that we frequently change our beliefs and behaviors to be similar to those of the people we care about—a process known as conformity. An important aspect of social-cultural psychology are social norms—the ways of thinking, feeling, or behaving that are shared by group members and perceived by them as  appropriate (Asch, 1952; Cialdini, 1993). Norms include customs, traditions, standards, and rules, as well as the general values of the group. Many of the most important social norms are determined by theculture in which we live, and these cultures are studied by cross-cultural psychologists. A culture represents the common set of social norms, including religious and family values and other moral beliefs, shared by the people who live in a geographical region (Fiske, Kitayama, Markus, & Nisbett, 1998; Markus, Kitayama, & Heiman, 1996;  Matsumoto, 2001). Cultures influence every aspect of our lives, and it is not inappropriate to say that our culture defines our lives just as much as does our evolutionary experience (Mesoudi,  2009). Psychologists have found that there is a fundamental difference in social norms between Western cultures (including those in the United States, Canada, Western Europe, Australia, and New Attributed to Charles Stangor Saylor. Norms in Western cultures are primarily oriented toward individualism, which is about valuing the self and one’s independence from others. Children in Western cultures are taught to develop and to value a sense of their personal self, and to see themselves in large part as separate from the other people around them. Children in Western cultures feel special about themselves; they enjoy getting gold stars on their projects and the best grade in the class. Adults in Western cultures are oriented toward promoting their own individual success, frequently in comparison to (or even at the expense of) others. Norms in the East Asian culture, on the other hand, are oriented toward interdependence or collectivism. In these cultures children are taught to focus on developing harmonious social relationships with others. The predominant norms relate to group togetherness and connectedness, and duty and responsibility to one’s family and other groups. When asked to describe themselves, the members of East Asian cultures are more likely than those from Western cultures to indicate that they are particularly concerned about the interests of others, including their close friends and their colleagues. Another important cultural difference is the extent to which people in different cultures are bound by social norms and customs, rather than being free to express their own individuality  without considering social norms (Chan, Gelfand, Triandis, & Tzeng, 1996). Cultures also differ in terms of personal space, such as how closely individuals stand to each other when talking, as well as the communication styles they employ. It is important to be aware of cultures and cultural differences because people with different cultural backgrounds increasingly come into contact with each other as a result of increased travel and immigration and the development of the Internet and other forms of communication. In the United States, for instance, there are many different ethnic groups, and the proportion of the population that comes from minority (non-White) groups is increasing from year to year. The social-cultural approach to understanding behavior reminds us again of the difficulty of making Attributed to Charles Stangor Saylor. Different people experience things differently, and they experience them differently in different cultures. The Many Disciplines of Psychology Psychology is not one discipline but rather a collection of many subdisciplines that all share at least some common approaches and that work together and exchange knowledge to form a  coherent discipline (Yang & Chiu, 2009). Because the field of psychology is so broad, students may wonder which areas are most suitable for their interests and which types of careers might be available to them. You can learn more about these different fields of psychology and the careers associated with them at http://www. Clinical and counseling psychologists provide therapy to These are the largest fields of patients with the goal of improving their life experiences. The focus is on the They work in hospitals, schools, social agencies, and in counseling assessment, diagnosis, causes, and private practice. This field uses sophisticated research methods, including reaction time and Cognitive psychologists work primarily in research Cognitive brain imaging to study memory, settings, although some (such as those who specialize in psychology language, and thinking of humans. Developmental These psychologists conduct research Many work in research settings, although others work in Attributed to Charles Stangor Saylor. Forensic psychologists apply psychological principles to understand Forensic psychologists work in the criminal justice the behavior of judges, attorneys, system. They may testify in court and may provide Forensic courtroom juries, and others in the information about the reliability of eyewitness testimony psychology criminal justice system. Health psychologists are concerned with understanding how biology, Health psychologists work with medical professionals in behavior, and the social situation clinical settings to promote better health, conduct research, Health psychology influence health and illness. There are a wide variety of career opportunities in these fields, generally working in businesses. These Industrial-organizational psychology psychologists help select employees, evaluate employee Industrial- applies psychology to the workplace performance, and examine the effects of different working organizational and with the goal of improving the conditions on behavior. They may also work to design environmental performance and well-being of equipment and environments that improve employee psychology employees. These psychologists study people and Most work in academic settings, but the skills of the differences among them. The goal is personality psychologists are also in demand in business— to develop theories that explain the for instance, in advertising and marketing. PhD programs Personality psychological processes of individuals, in personality psychology are often connected with psychology and to focus on individual differences. School psychologists work in elementary and secondary This field studies how people learn in schools or school district offices with students, teachers, School and school, the effectiveness of school parents, and administrators. They may assess children’s educational programs, and the psychology of psychological and learning problems and develop psychology teaching. Social and cross- This field examines people’s Many social psychologists work in marketing, advertising, cultural psychology interactions with other people. Topics organizational, systems design, and other applied Attributed to Charles Stangor Saylor. The goal is to understand the psychological factors that influence performance in sports, including the role of exercise and team Sports psychologists work in gyms, schools, professional Sports psychology interactions. Psychology in Everyday Life: How to Effectively Learn and Remember One way that the findings of psychological research may be particularly helpful to you is in terms of improving your learning and study skills. Psychological research has provided a substantial amount of knowledge about the principles of learning and memory. This information can help you do better in this and other courses, and can also help you better learn new concepts and techniques in other areas of your life. The most important thing you can learn in college is how to better study, learn, and remember. These skills will help you throughout your life, as you learn new jobs and take on other responsibilities. There are substantial individual differences in learning and memory, such that some people learn faster than others. But even if it takes you longer to learn than you think it should, the extra time you put into studying is well worth the effort. And you can learn to learn—learning to effectively study and to remember information is just like learning any other skill, such as playing a sport or a video game.
Journal as expanding consciousness in research purchase ditropan 5 mg free shipping, theory buy ditropan 2.5mg free shipping, and practice of Gerontological Nursing order 2.5mg ditropan with mastercard, 12, 16–18. Health as expanding consciousness (2nd sciousness in research, theory, and practice. Newman’s theory of health as expanding ple with dementia living in a nursing home. King Introducing the Theorist Introducing the Theory Use of King’s Conceptual System and Theory Summary Introducing the Theorist nursing adults in hospitals. While working my way through college, I worked in a physician’s ofﬁce as a My postsecondary education experiences included school nurse and as an occupational health nurse. John’s Hospital have always believed that as a teacher one must also School of Nursing in St. Louis, baccalaureate and be an excellent practitioner, so my experience as a master’s degrees in nursing from St. Louis Univer- teacher of nursing at undergraduate and graduate sity, and a doctor of education from Teachers levels included practice. Postdoc- sity, Chicago; the Ohio State University; and the toral study included work in advanced statistics, University of South Florida, advancing from assis- systems research, and computers. Continuing tant professor to full professor and now as profes- education is an ongoing process. The history, and philosophy with emphasis on science most recent are the Jessie Scott Award for Leader- and ethics. The University of Tampa (Society) Department of Nursing named the annual research award given to students the “Imogene M. I also appear in Who’s (Individuals) Who in America, American Women, and Who’s Who in Nursing. Introducing the Theory Continuous discoveries in telecommunications and technology, and a daily bombardment of infor- mation about world events bring complexity to one’s life that is unprecedented in history. As in- process for developing a conceptual system is dividuals, we are born, grow, and develop within explained. A goal attainment from my conceptual system is sense of a global community can be understood as demonstrated. The application of this conceptual we view the interactions of individuals and groups system and Theory of Goal Attainment is discussed with linguistic, ethnic, and religious differences. My ﬁrst theory publication pronounced the prob- The commonality in my worldview is human lems and prospect of knowledge development in beings who communicate and interact in their nursing (King, 1964). Over 30 years ago, the prob- small groups within their nations’ social systems; lems were identiﬁed as (1) lack of a professional that is, human environments as well as physical en- nursing language; (2) atheoretical nursing phe- vironments. Concept development is a continuous represent interconnected links for information pro- process in the nursing science movement (King, cessing in a high-tech world of health care and 1988). This conceptual system provides one ap- My rationale for developing a schematic repre- proach to structure a world community of human sentation of nursing phenomena was inﬂuenced beings, who are the recipients of nursing care. King’s Theory of Goal Attainment 237 interaction in those works inﬂuenced my ideas rel- framework”), and the result was the publication of ative to organizing a conceptual frame of reference a book entitled Toward a Theory of Nursing (King, for nursing, as shown in Figure 16–1. From being, commonly referred to as an “individual” or a my initial set of ideas in 1968 and 1971, my con- “person. For example, the concept of ings (ontology) and to the nature of knowledge perception has been studied in psychology for (epistemology). The literature indicated that most of the early studies dealt with sensory perception. From this research literature, I in systems research, I was introduced to a philoso- identiﬁed the characteristics of perception and de- phy of science called General System Theory (Von ﬁned the concept for my framework. This philosophy of science searching literature for knowledge of each of the gained momentum in the 1950s, although its roots concepts in my framework. Von Bertalanffy, credited “Searching for scientiﬁc knowledge in nursing is an with originating the idea of General System ongoing dynamic process of continuous identiﬁca- Theory, deﬁned this philosophy of science move- tion, development, and validation of relevant con- ment as a “general science of wholeness: systems of cepts” (King, 1975). A concept is elements in mutual interaction” (Von Bertalanffy, an organization of reference points. This philosophy different types according to the different sources of gave me the impetus to focus on knowledge their meaning.... A concept is a term to which development as an information-processing, goal- meaning has been assigned. System Theory provides a holistic approach to The concept development and validation study nursing phenomena as an open system and process is as follows: frees one’s thinking from the parts-versus-whole dilemma. Review, analyze, and synthesize research litera- ing, the central ideas revolve around the nature of ture related to the concept. From the characteristics, write a conceptual However, because a manuscript was due in the deﬁnition. Review literature to select an instrument or ceptual system (formerly called a “conceptual develop an instrument. Decisions are made on selection of the popula- cently, several dissertations by Frey (1995), Sieloff tion to be sampled. Generally speaking, nursing care’s goal is to help in- dividuals maintain health or regain health (King, Concepts that represent phenomena in nursing 1990). Twelve concepts—self, body image, role, percep- tion, communication, interaction, transaction, Concepts of self, perception, communica- growth and development, power, authority, organi- tion, interaction, transaction, role, and zation, and decision making—were identiﬁed from decision making were selected. The concepts that provided substantive knowledge The concepts of self, perception, communication, about human beings were placed within the per- interaction, transaction, role, and decision making sonal system, those related to groups were placed were selected. Self is an individual whose percep- within the interpersonal system, and those related tion and role inﬂuence that person’s communica- to large groups that make up a society were placed tion, interaction, and decision making in small and within the social system. So, what is the health-care system all of the concepts is used in nurses’ interactions within which nurses function? Is it a social system with individuals and groups within social organiza- of individuals and groups interacting to achieve tions, such as the family, the educational system, goals related to health? Knowledge of these con- in Figure 16–2, was developed that represented the cepts came from my synthesis of research in many process whereby individuals interact to set goals disciplines. The con- ment appears to be the primary goal of health-care cepts represent basic knowledge that nurses use in administrators and insurance companies. If the their role and functions either in practice, educa- goals and the means to achieve them are mutually tion, or administration. In addition, the concepts agreed upon by nurses and patients, 99 percent of provide ideas for research in nursing. Goal One of my goals was to identify what I call the attainment represents outcomes. Using the transaction process model is and foremost other human beings who give nurs- one way to achieve this goal. Recognizing that a conceptual process that can be observed in many situations system represents structure for a discipline, the when two or more people interact, such as in the next step in the process of knowledge develop- family and in social events (King, 1996). In your role as as one assesses the patient and the environment a nurse, after interacting with a patient, sit down and makes a nursing diagnosis, the concepts of per- and write down your behavior and that of the pa- ception, communication, and interaction represent tient. It is my belief that you can identify your per- knowledge the nurse uses to gather information ceptions, mental judgments, mental action, and and make a judgment. That is, did you exchange information to be attained, agree on the means to attain goals and set a goal with the patient? Did you explore the that represent the plan of care, and then implement means for the patient to use to achieve the goal? If not, you ask why, and the that most nurses use this process but are not aware process begins again. The pa- of the concepts and of the process, nurses have a tient’s record indicates the process used to achieve scientiﬁc base for practice that can be articulated goals. On discharge, the summary indicates goals clearly and documented to show quality care. One does not need multiple can a nurse document this transaction model in forms to complete when this documentation sys- practice? Why do nurses insist on designing critical Documentation System paths, various care plans, and other types of forms A documentation system was designed to imple- when, with knowledge of this system, the nurse ment the transaction process that leads to goal at- documents nursing care directly on the patient’s tainment (King, 1984a). Why do we use multiple forms to complicate nursing process of assess, diagnose, plan, imple- a process that is knowledge-based and also provides ment, and evaluate, which I call a method.
This intermediate is then cyclized purchase 5mg ditropan with mastercard, oxidized and dehydrated to give the quinoline system purchase 5 mg ditropan with visa. Friedlnder synthesis itself is somewhat complicated because of the difﬁculty in preparing the necessary 2-aminoaryl carbonyl compounds buy ditropan 5 mg online. Again, tetrahydroisoquinoline can be aro- matized by palladium dehydrogenation to produce an isoquinoline system. While this substitution takes place at C-2 and C-4 in quinoline, isoquinoline undergoes nucleophilic substitution only at C-1. Indole is a ten p electron aromatic system achieved from the delocalization of the lone pair of electrons on the nitrogen atom. Benzofuran and benzothiaphene are very similar to benzopyrrole (indole), with different hetero-atoms, oxygen and sulphur respectively. A number of important pharmacologically active medicinal products and potential drug candidates contain the indole system. For example, serotonin, a well known neurotransmitter, has a substituted indole system. Preparation of indole Fischer indole synthesis Cyclization of arylhydrazones by heating with an acid or Lewis acid catalyst yields an indole system. The disadvantage of this reaction is that unsymmetrical ketones give mixtures of indoles if R0 also has an a- methylene group. As an electron-rich heterocycle, indole undergoes electrophilic aromatic substitution primarily at C-3, for example bromination of indole. When tryptophan is broken down, the presence of indole can be detected through the use of Kovacs’ reagent. Kovacs’ reagent, which is yellow, reacts with indole and produces a red colour on the surface of the test tube. Nucleic acids are biopolymers made of nucleotides joined together to form a long chain. These biopolymers are often found associated with proteins, and in this form they are called nucleoproteins. Each nucleotide comprises a nucleoside bonded to a phosphate group, and each nucleoside is composed of an aldopentose sugar, ribose or 2-deoxyribose, linked to a heterocyclic purine or pyrimidine base (see Section 4. In deoxyribonucleotides, the heterocyclic bases are purine bases, adenine and guanine, and pyrimidine bases, cytosine and thymine. In ribonucleo- tides, adenine, guanine and cytosine are present, but not thymine, which is replaced by uracil, another pyrimidine base. When the sugar is a part of a nucleoside, the 0 0 0 numbering of sugars starts with 1 , i. C-1 becomes C-1 , for example 2 - 0 0 deoxyadenosine 5 -phosphate and uridine 5 -phosphate. To carry out phosphorylation at C-5 ,0 the other two hydroxyl functionalities at C-20 and C-30 have to be protected, usually with an isopropylidine group. At the ﬁnal step, this protecting group can be removed by mild acid-catalysed hydrolysis, and a hydrogenolysis cleaves the ben- zylphosphate bonds. In the nucleic acids, these phosphate ester links provide the nucleic acids with a long unbranched chain with a ‘backbone’ of sugar and phosphate units with heterocyclic bases sticking out from the chain at regular intervals. One end of the nucleic acid polymer has a free hydroxyl at C-30 (the 3 -end0 ), and the other end has a phosphate at C-50 (the 5 -end0 ). The actual base sequences for many nucleic acids from various species are available to date. Adenine and thymine are usually present in equal amounts; so are cytosine and guanine. The two strands run in opposite directions and are held together by hydrogen bonds between speciﬁc pairs of bases. Adenine and thymine form strong hydrogen bonds to each other, but not to cytosine or guanine. Similarly, cytosine and guanine form strong hydrogen bonds to each other, but not to adenine or thymine. The pitch of the helix is such that ten successive nucleotide pairs form one complete turn in 34 A˚ (the repeat distance). The exterior width of the spiral is about 20 A,˚ and the internal distance between 1 -positions0 of ribose units on opposite chains is about 11 A. This complementary pairing of bases explains why A and T are always found in equal amounts, as are C and G. The two strands of the double helix coil in such a way that two types of ‘groove’ are formed, a major groove 1. A number of ﬂat, polycyclic molecules ﬁt sideways into the groove between the strands and intercalate, or insert themselves, between the stacked base pairs. This process reads the stored genetic information and brings it out of the nucleus to ribosomes, where protein synthesis occurs. As the strands separate and bases are exposed, new nucleotides line up on each strand in a complementary fashion, A to T, and C to G. Two new strands now begin to grow, which are complementary to their old template strands. The most important step is the addition of a 5 -mononucleoside0 triphosphate to the free 3 -hydroxyl0 group of the growing chain as the 3 -hydroxyl0 attacks the triphosphate and expels a diphosphate leaving group. The strand that gets transcribed is known as the template strand or antisense strand. Ribosomes are small granular bodies scattered throughout the cytoplasm, and this is the place where protein synthesis starts. This technique was ﬁrst developed in 1985, originally used to detect the presence of genetic diseases. Twenty different amino acids are used to synthesize proteins, and these are alanine (Ala, A), arginine (Arg, R), asparagine (Asn, N), aspartic acid (Asp, D), cysteine (Cys, C), glutamine (Gln, Q), glutamic acid (Glu, E), glycine (Gly, G), histidine (His, H), isoleucine (Ile, I), leucine (Leu, L), lysine (Lys, K), methionine (Met, M), phenylalanine (Phe, F), proline (Pro, P), serine (Ser, S), threonine (Thr, T), tryptophan (Trp, W), tyrosine (Tyr, Y) and valine (Val, V). The shape and other properties of each protein are dictated by the precise sequence of amino acids in it. Most amino acids are optically active, and almost all the 20 naturally occurring amino acids that comprise proteins are of the L-form. While the (R) and (S)-system can be used to describe the absolute stereochemistry of amino acids, conventionally the D and L-system is more popular for amino acids. A protein is made up of one or more polypeptide chains, each of which consists of amino acids. Instead of writing out complex formulae, sequences of amino acids are commonly written using the three- or one-letter codes e. The ends of a peptide are labelled as the amino end or amino terminus, and the carboxy end or carboxy terminus. It is the structure of the R group (side chain) that determines the identity of an amino acid and its special properties. The side chain (R group), depending on the functional groups, can be aliphatic, aromatic, acidic, basic, hydroxylic, sulphur containing or amidic (containing amide group). However, proline has an unusual ring structure, where the side chain is bonded at its terminus to the main chain nitrogen. For amino acids, a zwitterionic structure is possible because the basic amino group can accept a proton and the acidic carboxylic group can donate a proton. However, many higher animals are deﬁcient in their ability to synthesize all of the amino acids they need for their proteins. Human beings also must include in their diet adequate amounts of eight different amino acids, which they cannot synthesize in their body. The eight essential amino acids are valine, leucine, isoleucine, phenylalanine, tryptophan, threonine, methionine and lysine. Sometimes, arginine and histidine are also included in the category of essential amino acids. Several amino acids can be classiﬁed as glucogenic and ketogenic because of their degradation products. Amino acids that are converted to glucose or glycogen are called glucogenic amino acids. Alanine, arginine, asparagine, cysteine, glutamine, glycine, histidine, hydroxyproline, methionine, proline, serine and valine are glucogenic amino acids. Amino acids that give rise to ketone bodies (acetylCoA or acetoacetyl- CoA, neither of which can bring about net glucose production) are called ketogenic amino acids. However, the liver is the major site of metabolism of nitrogenous compounds in the body. Digestion of dietary proteins produces amino acids, which are absorbed through epithelial cells and enter the blood.
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