Spider Silk: Structure, Function and Uses

Spider Silk: Structure, Function and Uses Spider silk, also known as gossamer, is a fiber spun by spiders. Spider silk is a remarkably strong. Its tensile strength is comparable to that of high-grade steel. The term silk normally refers to a wide range of continuous filaments spun by the several species of Lepidoptera and Arthropoda, used for building structures for various purposes including prey capture. Silk filaments spun by spiders and silkworms possess superior properties than other silk producing insects and more than 2500 orb weaving species existing worldwide [1 4]. Spiders have six or seven sets of glands, each producing a different fiber. These glands remained undifferentiated, early in the evolution [4 7]. The spinnerets, microscopic tubes originating from glands, are classified into major and minor ampullate. The term ampulla is used to describe the distal part of the secretary zone [8]. Unlike synthetic polymers, the biopolymers are composed of numerous monomers arranged in a strictly controlled manner [9]. M any attempts have been made in the past to harvest and convert spider silk filaments into fabric form [4, 10, 11]. Scientists have been hard at work attempting to marshal the power of spider silk for a range of medical applications-including wound-care applications; suture materials; muscle, bone, cartilage, tendon, and ligament repair scaffolds. Spider silk possesses mechanical attributes such as very high tensile strength and elasticity, making it one of the toughest fibers known to man. The problem is that spiders dont produce enough silk to render it marketable for mass human use. SPIDER WEB AND TYPES OF SPIDER SILK: Prior to the exploration of the structure and properties of spider silks, construction and design of webs have been the major area of focus. The spider webs can take a variety of forms but the most common type is the orb web. Different families of spiders like Araneus, Nephila builds orb web and other families of spiders construct tangle and sheet webs [33, 35]. Orb-web spiders invest little energy in searching for prey. It spends most of its time synthesising silk and constructing webs. An orb web has several spokes laid outward from a common origin. However, this varies amongst the various species of spiders [31]. The orb webs are often constructed with an orientation to avoid being damaged due to the air drag caused by prey capture [24]. In a three dimensional web, the energy required to stop a moving insect is dissipated mainly by breaking some of the strands. In a two dimensional orb web, it is achieved through stretching the spiral threads [29]. Due to high-energy requirement in protein synthesis, only the damaged parts of the web are reconstructed instead of the whole web. Large portions of the web are repaired through the enzyme digestion and recycling. Based on the vibrations of the strands, the spider locates the prey accurately. The orb-weaving spiders are able to synthesize as many as seven different types of silk [13-15] including dragline by drawing liquid crystalline proteins from separate gland-spinneret complex. The perfume-coated dragline helps to find their mates, swing from place to place, store food, eggs and for reproduction. Capture threads produced by the flagella form glands of Nephila Clavipes is highly compliant. Both Araneus and Nephila coat their capture threads with an aqueous solution that forms sticky droplets which enhances damping and harvests water from air [25]. Its principal function is to absorb and dissipate the kinetic energy of captured flying insects. [3]. The chemical composition of the aqueous solution of the adhesive spiral varies among the species qualitatively and quantitatively. The variation is mainly due to physical environment, diet, web recycling, and onto genetic changes in the web chemistry. SPINNING OF SPIDER SILK: Many spiders are active at night and their colorations are usually orange, brown, grey and black, to reduce the spiders visibility during day time. Silk secreting systems of spiders and insects are homologous and linked to the crural gland and cuticular secretions [6]. Cephalothorax of the spider attached to an unsegmented abdomen, which has spinnerets at the posterior end [33]. N.clavipes spider has three pairs of spinnerets namely, anterior lateral, posterior lateral and posterior median. The largest major ampullate gland secretes dragline silk protein, exits from the anterior lateral spinneret. Secretions of proximal region and the distal region together form spider silk. Proximal region secretions are rich in tyrosine residues, sulfhydryl linkages and acidophilic nature. They form core of the silk while secretions of distal zone form coating of the fiber, which lacks tyrosine and sulfur contents. A mature Nephila produces dragline silk fiber at approximately 1 cm/sec during web construction and can increase up to 10 times faster during a rapid descent [52]. Spider silk spun under water displays greater stiffness and resilience compared to silk spun naturally in air [53]. The diameter of the silk can be controlled by the valve located at the end of the duct [47]. The spiders have the ability to withstand temperature variation of up to 30oC and humidity variation of up to 70% [20]. Spiders can easily modify the spinning conditions by their moving speed, building the webs in different times in a day. Spinning speed has less influence on the diameter of the filament when compared to the temperature even though its influence on toughness. COMPOSITION OF SILK: Variability in silk spun by the spiders exists at different levels such as in inter-specific (between species), intra-specific (within same species) and intra individual levels [54]. The factors that affect variations in silk structure and properties include body dimensions, body weight, rate and temperature of reeling and spinning direction [17, 25]. Composition of silks produced by herbivorous spiders is rich in Glycine, Alanine and Serine. This type of silk can be predicted to some extent. However, the silk produced by predatory spider, cannot be predicted due to the different types of prey [40, 55]. Dietary compositions of herbivorous spiders are energy rich and poor in protein content whereas the diet of predatory spiders is more diverse and rich in protein. Competition for limited or fluctuating supplies of amino acid perhaps has resulted in the evolution of two different kinds of glands to secrete protein glues and silk fibroin. The spider produces the thr ead on a very strict energy budget using liquid crystalline polymer. STRUCTURE AND PROPERTIES: Spider silk has drawn attention from all the sections of engineering due to its superior properties when compared to existing fibrous materials such as the silkworm silk. Spider silk cannot be compared with silkworm silk. This is because spiders are difficult to raise in large numbers and their silk lacks the lustre of silkworm silk. The chemical compositions of various silks vary with the type of function they are intended to perform. In addition to the fibroin, other classes like glycoprotein , inorganic salts, sulphur containing compounds, amino acids, and ionic forms of amines are also present in the spider silk [69, 70]. Presences of these chemicals play crucial roles in identification of species, regulation of water content of the web and protection against microorganisms. Presence of 12- methyltetradecanic acid and 14-methyl hexadecanoic acid in less amounts impart antimicrobial properties to the spider silk. Wax like esters are also present in the su rface of the spider silk. Macroscopic Structure of Dragline Silk: Dragline spider silk is golden yellow in color and has circular cross section with a mean diameter of about 7 ÃŽÂ ¼m [19, 38, 54]. It lacks glue-like protein, similar to that of silkworm silk, as its associated with dragline fiber [56]. The dragline spider silk consists of semi crystalline polymeric structures with numerous small crystallites between amorphous regions. The mechanical properties of the dragline silk are highly influenced by the composition of the amino acids, insect size, diet, body temperature and drawing speed [99, 124]. The breaking strength of silk increases linearly with increasing spider weight and breaks at stress of about six times the spiders weight [47, 100, 129]. The average tensile strength of the dragline of Nephila clavipes is almost three times that of Bombyx mori (1.3 0.5 GPa, respectively). Tensile strength of spider silk reduces, when it is subjected to acidic rain and UV radiation [133]. Spider silks can u ndergo large tensile and compression deformations. The ability of spider silk to resist transverse compression is lower than that of many textile fibers like Kevlar 29, nylon 5, polyester and wool. REGENERATED SPIDER SILK PROTEIN BY ARTIFICIAL ROUTE: Forced Silking (Reeling) of Spider Silk Reeling devices have been developed for forced silking of dragline from the glands of anaesthetized Nephila clavipes [78, 115,140, 141] to reel about 3-5 mg of silk in one session. Splicing of silk genes into two different cell lines have been tried in the past using bovine mammary cells and hamster kidney cells, to produce large volumes of recombinant proteins [49, 135]. Successful sequencing of genes of the flagella form silk of tropical spider Nephila clavipes and N. madagascariensis has been achieved lately [39]. Recombinant DNA technology for microbial proteins [144, 150, 151] appears to be advantageous compared to that of chemical synthesis due to low cost, rapid preparation and absence of by-products. A team of researchers at the University of Notre Dame (Notre Dame, IN) the University of Wyoming (Laramie), and Kraig Biocraft Laboratories Inc. (Lansing, MI) have succeeded in producing transgenic silkworms. The advantage of these animals is that they can spin artificial spider silk with strength and flexibile attributes similar to those of native spider silk. Until this breakthrough, only very small quantities of artificial spider silk had been produced in the laboratories. Kraig Biocraft believed these limitations can be overcome through use of recombinant DNA. This biotechnological approach can be used to produce silk fibers with a broad range of physical properties or with predetermined properties optimized for specific biomedical or other applications. From the known sequence of the spider silk protein, genes are constructed and expressed using E. Coli as the host, which has been successfully used earlier for silkworm silk [160]. Genes of spider dragline silk have been inserted into mammary gland cells along with regulatory elements. Insertion of the genes into eggs of single cell goat has been tried. This was purposely done to produce water-soluble silk protein [154, 156, 165]. Few milligrams of genetically engineered silk like protein has been successfully produced based on the sequence of spider protein [155]. APPLICATIONS: Though availability of the dragline silk is limited, it is widely used in defence [4,] and medical [11] applications. Structural similarity and comparable properties of dragline and Kevlar [127, 180] makes it more attractive for applications where high performance, in terms of physical properties is in demand. Until World War II, spider silk was used as crossed-hairs in optical devices including microscopes, telescope and bomb guiding systems [4]. Silk strands of the web have an ability to elongate when an insect is caught, convert the preys momentum i.e. kinetic energy into heat, and dissipate about 70% of the converted energy. The web also gently rebounds so as not to catapult the insect back out. This ability to dissipate energy at very high strain rates makes spider silk suitable for body armour system and ideal for ballistic protection [131, 140]. Though biodegradability is a helpful aspect for sutures, it is as unwanted in high performance applications such as bulletproof vests. A very low glass transition temperature of -50o C to 60o C enables it to absorb sudden shocks at low atmospheric temperature and makes the spider silk suitable for parachute applications. However, super contraction in water is undesirable for use in the fabrication of parachutes [174, 175]. Earlier use of spider silk in the form of web, rather than a fiber, includes wound dressing to help blood clot and fishing nets. Spider silk protein can be used to coat the medical implants for better performance. Surgical thread, biomembranes and scaffolds for tissue engineering are the possible areas of application in biomedical and biomaterial fields. Due to low inflammatory potential of silk proteins and antithrombic nature, recombinant spider silk has potential applications in sutures for eye surgery, artificial tendon and ligaments for knee construction. Spider silk with higher safety co-efficient can be used in structural applications like elevator ropes, bridges and pillars [100]. CONCLUSION The dragline silk offers excellent physical and chemical properties that can withstand adverse and extreme conditions than many of the existing natural and synthetic fibers. Though the chemical synthesis seems to be unfruitful in many aspects, the recombination method of producing the spider silk using biological hosts proves to be a viable option for producing the spider silk in a large scale. In spite of various successful attempts made in the production of dragline silk in the laboratory scales, controlling the molecular conformation and their aggregation during the spinning for achieving properties similar to the native fiber still remains as a challenge to be addressed through future research.

Essay --

Introduction A marketing plan is a document which comprises of analysis of the current marketing situation, threats and opportunities of the firm, marketing objectives and strategy specified that has the 4 Ps, program of actions, and projected budget and income and other financial statements (Drummond, Ensor, & Ashford, 2008). The marketing plan consist of 3 main steps: 1) Planning Phase 2) Implementation Phase 3) Control Phase Figure: 3 Phases of Marketing Plan (Source: (Drummond, Ensor, & Ashford, 2008) ) A documented market plan helps in tracking the progress of the company or activity by providing a point of reference. While creating a new market plan around three end goals should be kept in mind. Having end goal in mind will help in efficient formulation of marketing Plan. Placing more goals will lead to dilution of efforts and shortage of resources for the company (Luke, 2013). Aim The report is creating a marketing plan for Tata global beverages limited to launch into Australian market with their new Green tea product. History Tata global beverage was set up as a joint venture between Tata Sons and the UK-based tea plantation company, James Finlay and Company in 1962. Tata Tea was born in 1983 after James Finlay sold his shareholding to Tata. The company set out on a path with global ambitions, evidenced by the acquisition of Tetley in 2000. This was followed by a string of strategic acquisitions including Good Earth, Jemca, Vitax, Eight O’ Clock Coffee and Himalayan Water (Tata Global Beverages, 2014). Source: (Tata Global Beverages, 2014). Following are different brands that come under Tata beverages: Source: (Tata Beverages, 2014) Tata Beverages has a wide variety of portfolio of products which ranges from dis... ...ers never asked for or thought were possible example Walkmans. Companies are trying to become more market driven and their major efforts go in retaining customers. Customer retention has become much more important than customer attraction because attracting new customer costs five times more than pleasing an existing one. (Kotler, Marketing Management Millenium Edition, 2002). Target Market The product will be targeting the following segment of population: 1) People from the age range of 15 to 35 both male and females. 2) Health conscious people preferably involved in regular work out. 3) People who are trying to switch to a healthier lifestyle and want to give up soft drinks. Competitor Analysis Competition is the most critical factor in marketing management and includes all of the actual and potential rival offerings and substitutes that a buyer might consider.

Advertising Effects On Young People Essay

Advertising on American youth has changed somewhat in the last ten years. Today’s youth, mostly between the ages of 15-18, see an advertisement on television, or the internet and they want to try it , have it, or even steal for it because they desire it. Take alcohol advertisements for instance. Alcohol advertisements are more complex and appealing to today’s youth than they were ten years ago. The effect of these alcohol related advertisements, cause our youth to try just a little sip or worse drink to many. Because our youth today don’t understand the effect of alcohol on them, they get behind the wheel of a vehicle and either cause an accident where they hurt or kill themselves or they hurt or kill someone else. Alcohol advertisements were not as appealing ten years ago as they are today. Really all you would see were a few beer advertisements and the â€Å"Drink Responsibly† at the end of it. Honestly, who really drinks responsibly these days? I don’t believe that our American youth does or there would not be that many drunk driving accidents involving our youth. As far as technology advertisements, they are just as bad. The effects of these advertisements are a hundred times worse on today’s youth than they were ten years ago. Therefore, the effects of advertising on today’s young population has increased the potential for success, however there is still non-targeted advertisement that reaches out to today’s American youth in a potentially negative perspective. Television is the dominant way to advertise to American youth because that is what our youth spends most of their time doing. By searching online for evidence that could support this, I found these statistics from thinkbox.tv: â€Å"Ages 15-24 spend 43% of their time watching television. Young people particularly like commercial television, which accounts for 76% of ages 16-34. Commercial television reaches 62% of the 16-34 population every day, 89% every week, and 97% every month. Of ages 5-16, 45% talk about their favorite television program with friends and family. Of ages 5-16, 34% say they regularly visit their favorite television website or Facebook page. 10% of ages 5-16, watch television on their laptops or computers in their rooms† (http://www.thinkbox.tv/getting-started-on-tv/discover-the-power-of-tv-advert  ising/#2). These statistics can somewhat show that the youth today spends more time watching television and playing on their computers than they do outside. Furthermore, television has become a powerful piece of technology for today’s youth. For example, the variety of channels that is now available for our youth. For that reason, television is the main source of advertising to our youth today. Advertising today vs ten years ago can raise a lot of viewpoints among Americans today. Most people will argue that advertisements do not cause any effects on our youth, but I disagree. For instance, cigarette advertisements effect our youth in some way. Some young people choose to ignore these advertisements because they know it harms the body, while others choose to go purchase cigarettes because they think it makes them fit in more with their peers. I have seen more young people with a cigarette today than I did ten years ago. In addition to the cigarette advertisements, the alcohol advertisements raise concern with some. Alcohol advertisements tend to persuade our young people that its ok to drink as long as you drink responsibly. There is not one young person that says â€Å"Ok, I will only have a couple of drinks†. Young people tend to do what they think will make them more acceptable in today’s society. To me, this is unacceptable behavior. In a similar fashion, Violence has taken over our youth today. The video games that most young people play portray violence in a very bad way. Some gangs or â€Å"clicks† use this type of violence as an initiation for young people to join. I have seen more teen tragedies in today’s news due to this type of violence than the last ten years. There is teen kidnappings, violent injuries and even murders. Most of the time, it is teen on teen violence because they think its ok because they see it on television or even the internet. It is ridiculous on how much violence has happen with today’s youth. I believe it is because of all the advertisements that portray violence has an ok thing. For example, video games are the main source of violence in today’s youth. My opinion on this type of advertising is one of the causes of most of our youth’s accidents, tragedies, and even deaths. Today’s advertising has more effect on our youth than it did ten year s ago. In conclusion, advertising on American youth has caused tragedies and even death. Young people today really don’t have enough common sense to know that if it looks, taste, or smells bad, that it probably is and that they should not partake in it. Our young people today seem to think that if they partake in things that could hurt them then it makes them fit in more with their peers. To clarify, â€Å"If you can drink this or smoke this or even try this, then you can be part of this â€Å"click†. It sickens me to know that even our youth today has effects on other young people. Parents should monitor more of what their child is doing, what they are watching and what kind of people their child is friends with. In another sense, parents could prevent tragedies or even death from occurring. Yes, advertising in some way has increased the potential for success in American youth; however it still has potentially negative perspectives on American youth today. By parents monitoring what their child is watching, what their child is doing, and what kind of people their child is friends with can potentially decrease the amount of smoking, drinking, and violence that our young people partake in today. There is always positive potential for our American youth. We just have to monitor more of what they watch and make sure that they know right from wrong. http://www.thinkbox.tv/getting-started-on-tv/discover-the-power-of-tv-advertising/#2 THESIS AND OUTLINE The effects of advertising on today’s young population has increased the potential for success, however there is still non-targeted advertisements that reaches out to today’s American youth in a potentially negative perspective. I. Introduction Paragraph A. The relation between advertising today verses ten years ago. B. The effects on American youth today verses ten years ago. C. Thesis Statement II. Body Paragraph A. Topic Sentence on the focus of the paragraph B. Specific examples of the effects of advertising on today’s youth. C. My explanation and analysis of my examples. D. Summary Sentence III. Body Paragraph A. Topic Sentence that identifies opposing viewpoints. B. My explanation on why I disagree C. Examples of why I disagree D. Summary Sentence IV. Conclusion Paragraph A. Summary of my body paragraphs B. Thesis statement reiterated C. My final thoughts or call for action

Medicinal Practices from the American Revolution to the...

Medicinal Practices; American Revolution to the War of 1812 For centuries, war has consumed millions of souls. It has caused heartache and has torn families apart. Today, properly educated doctors and nurses can treat wounds and injuries with proper care, but this taken for granted assistance wasn’t always readily available. In the Revolutionary War and the War of 1812, nearly 30,000 American soldiers died. However, rather than being killed on the battlefield, the majority of soldiers died while being treated in medical tents. More often then not, the work of doctors and surgeons resulted in worsening the state of their patients, frequently causing their death. Medical practitioners did more damage than deed to soldiers during the American Revolution to the War of 1812 because of their little attention to individual patients, housing for patients, poor work ethics and habits, lack of knowledge and because major medical advancements weren’t achieved for another half-century. Throughout the Revolutionary War and the War of 1812, doctors gave little attention to individual patients which resulted in the death of many soldiers. Dr. Gregg Baran, a physician and reenactor asserted, â€Å"At the time of a battle its important to realize there’d be one surgeon and one assistant for perhaps as many as 1000 soldiers,† (PBS Video). How can a doctor be effective if they have that many patients to take care of? Statistics show they weren’t. After being hit with a musket ball, there was aShow MoreRelatedThe De Goya Y Lucientes1809 Words   |  8 Pagesin 1786. Six years later, he suffered an awful illness which ultimately left him deaf and shaped his future work. After Napoleon Bonaparte rose to prominence during the French Revolution, Spain was invaded due to its political and strategic importance to the French. Goya was able to capture the horrors he saw in his anti-war works produced in paintings and with intaglio prints which he didn’t make public. The throne of Spain was taken by Jose ph Bonaparte, Napoleon s brother, who was backed by a largeRead MoreMandinka Empire21578 Words   |  87 Pagesoffer here a theory of â€Å"cultural convergence,† as a corollary to Darwin’s natural selection, regarding how slave Creoles and culture were formed among the Gullah and, by extension, supported by other examples, in the Americas. When numerous speakers from different, and sometimes related, ethnic groups have words with similar sounds and evoke related meanings, this commonality powers the word into Creole use, especially if there is commonality with Southern English or the host language. This theory