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Becky Kriger

Carbohydrates and Polysaccharides - 0 views

www.rsc.org/...carbohydrates.htm

Carbohydrates polymers Polysaccharides

shared by Becky Kriger on 08 Dec 08 - Cached
  • Disaccharide Monosaccharides sucrose from α-glucose + α-fructose maltose from α-glucose + α-glucose α-lactose * from α-glucose + β-galactose * Lactose also exists in a beta form, which is made from β-galactose and β-glucose
  • A condensation reaction takes place releasing water. This process requires energy. A glycosidic bond forms and holds the two monosaccharide units together.
  • Carbohydrates (also called saccharides) are molecular compounds made from just three elements: carbon, hydrogen and oxygen. Monosaccharides (e.g. glucose) and disaccharides (e.g. sucrose) are relatively small molecules.
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  • a source of energy
  • building blocks for polysaccharides (giant carbohydrates
  • components of other molecules eg DNA, RNA, glycolipids, glycoproteins, ATP
  • Monosaccharides are the simplest carbohydrates and are often called single sugars.
  • Monosaccharides have the general molecular formula (CH2O)n, where n can be 3, 5 or 6.
  • n = 3 trioses, e.g. glyceraldehyde n = 5 pentoses, e.g. ribose and deoxyribose ('pent' indicates 5) n = 6 hexoses, e.g. fructose, glucose and galactose ('hex' indicates 6)
  • Molecules that have the same molecular formula but different structural formulae are called structural isomers.
  • Monosaccharides containing the aldehyde group are classified as aldoses, and those with a ketone group are classified as ketoses. Aldoses are reducing sugars; ketoses are non-reducing sugars.
  • in water pentoses and hexoses exist mainly in the cyclic form, and it is in this form that they combine to form larger saccharide molecules.
  • There are two forms of the cyclic glucose molecule: α-glucose and β-glucose.
  • Two glucose molecules react to form the dissacharide maltose. Starch and cellulose are polysaccharides made up of glucose units.
  • Galactose molecules look very similar to glucose molecules. They can also exist in α and β forms. Galactose reacts with glucose to make the dissacharide lactose.
  • However, glucose and galactose cannot be easily converted into one another. Galactose cannot play the same part in respiration as glucose.
  • Fructose reacts with glucose to make the dissacharide sucrose.
  • Ribose and deoxyribose are pentoses. The ribose unit forms part of a nucleotide of RNA. The deoxyribose unit forms part of the nucleotide of DNA.
  • Monosaccharides are rare in nature. Most sugars found in nature are disaccharides. These form when two monosaccharides react.
  • The three most important disaccharides are sucrose, lactose and maltose.
  • Disaccharides are soluble in water, but they are too big to pass through the cell membrane by diffusion.
  • This is a hydrolysis reaction and is the reverse of a condensation reaction. It releases energy.
  • Monosaccharides are converted into disaccharides in the cell by condensation reactions. Further condensation reactions result in the formation of polysaccharides. These are giant molecules which, importantly, are too big to escape from the cell. These are broken down by hydrolysis into monosaccharides when energy is needed by the cell.
  • Monosaccharides can undergo a series of condensation reactions, adding one unit after another to the chain until very large molecules (polysaccharides) are formed. This is called condensation polymerisation, and the building blocks are called monomers. The properties of a polysaccharide molecule depend on: its length (though they are usually very long) the extent of any branching (addition of units to the side of the chain rather than one of its ends) any folding which results in a more compact molecule whether the chain is 'straight' or 'coiled'
  • Starch is often produced in plants as a way of storing energy. It exists in two forms: amylose and amylopectin
  • Amylose is an unbranched polymer of α-glucose. The molecules coil into a helical structure. It forms a colloidal suspension in hot water. Amylopectin is a branched polymer of α-glucose. It is completely insoluble in water.
  • Glycogen is amylopectin with very short distances between the branching side-chains.
  • Inside the cell, glucose can be polymerised to make glycogen which acts as a carbohydrate energy store.
  • Cellulose is a third polymer made from glucose. But this time it's made from β-glucose molecules and the polymer molecules are 'straight'.
  • Cellulose serves a very different purpose in nature to starch and glycogen. It makes up the cell walls in plant cells. These are much tougher than cell membranes. This toughness is due to the arrangement of glucose units in the polymer chain and the hydrogen-bonding between neighbouring chains.
  • Cellulose is not hydrolysed easily and, therefore, cannot be digested so it is not a source of energy for humans.
Becky Kriger

Polysaccharides: Their Structure and Function - 0 views

molecular-biology.suite101.com/...polysaccharides

Polymers Polysaccharides

shared by Becky Kriger on 08 Dec 08 - Cached
  • Polysaccharides are the complex carbohydrates. They are made up of chains of monosaccharides (the sugars) which are linked together by glycosidic bonds, which are formed by the condensation reaction
  • Cellulose is a major component of plant cell walls. It is an unbranched polymer with about ten thousand glucose units per chain. Hydroxyl groups (-OH) project out from each chain, forming hydrogen bonds with neighbouring chains which creates a rigid cross-linking between the chains, making cellulose the strong support material that it is.
  • Chitin is closely related in structure to cellulose, also being an unbranched polysaccharide. However, instead of the hydroxyl groups (-OH), the chains have the following structure –NH.CO.CH3 replacing it. Large amounts of chitin is found in the cuticles of arthropods, with smaller amounts being found in sponges, molluscs and annelids.
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  • Polysaccharides make ideal storage molecules for energy for a number of reasons; a) they are large, this makes them insoluble in water and therefore they exert no osmotic or chemical effect on the cell; b) they fold into compact shapes; c) they are easily converted into the required sugars when needed.
  • Glycogen is a branched polysaccharide found in nearly all animal cells and in certain protozoa and algae.
  • In humans and other vertebrates it is principally stored in the liver and muscles and is the main form of stored carbohydrate in the body, acting as a reservoir of glucose
  • Starch is similar to glycogen, however it is found in plant cells, protists and certain bacteria.
  • The starch granules are made up of two polysaccharides, amylose and amylopectin. Amylose is an unbranched molecule made up of several thousand glucose units, coiled helically into a more compact shape. Amylopectin is also compact but has a branched structure and is made up of twice as many glucose units as amylose.
  • For example, peptidoglycans, which are a combination of protein and polysaccharide and are found in the cell wall of certain bacteria. Glycolipids, a combination of polysaccharides and lipids are found in the cell membrane.
Justin Shorb

Window on the Solid State - Unit Cell - 0 views

www.jce.divched.org/...unit_cell_two_d_metal.htm

cell unit

shared by Justin Shorb on 24 Sep 08 - Cached
  • Note that the edges of these cells all connect lattice points in the structure, points with the same environments.
    • Justin Shorb
      Justin Shorb on 24 Sep 08
       
      Be sure that when you draw a unit cell, if you place the 'left' edge against the 'right' edge, they have the same lattice points touching!
  • Justin Shorb on 24 Sep 08
     
    Helpful for Exam I #3
  • Justin Shorb on 24 Sep 08
     
    Useful for understanding how Unit Cells work
Justin Shorb

Chemistry: The Molecular Science - Google Book Search - 0 views

books.google.com/books

109h density unit cell

shared by Justin Shorb on 24 Sep 08 - Cached
  • Chemistry : the molecular science
  • 8.8 Formal Charge
  • Justin Shorb on 24 Sep 08
     
    Helps to answer Exam I #4
  • Justin Shorb on 24 Sep 08
     
    Page in Moore et al. text about Unit cells.
Becky Kriger

Polysaccharides - Chemistry Encyclopedia - 0 views

www.chemistryexplained.com/...Polysaccharides.html

shared by Becky Kriger on 08 Dec 08 - Cached
  • Polysaccharides are long polymers of monosaccharides and their derivatives. Unlike proteins or nucleic acids, these polymers can be either linear or branched, and they can contain only one type of monosaccharide (homopolysaccharides), or more than one (heteropolysaccharides)
  • Starch is a homopolysaccharide and has two forms: amylopectin and α-amylose. In nature, starch is approximately 10 to 30 percent α-amylose.
  • Starch is the main energy reserve in plants; glycogen is the main energy reserve in animals
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  • In contrast to amylopectin, which comprises 70 to 90 percent of natural starch, α-amylose is a branching polysaccharide.
  • Branches occur at every twelve to thirty residues along a chain of α (1→4) linked glucoses. As a result, amylopectin has one reducing end and many nonreducing ends.
  • Amylopectin and α-amylose are broken down by the enzyme amylase. In animals, salivary α-amylase begins the digestion process in the mouth. Pancreatic α-amylase continues the process in the intestine.
  • Glycogen is the energy storage carbohydrate in animals. Glycogen is found mainly in the liver (where it is responsible for up to 10 percent of liver mass) and skeletal muscle (1 to 2 percent of skeletal muscle mass)
  • However, glycogen branches more abundantly than amylopectin, with branches at every eight to twelve residues. As a result, it has many more nonreducing ends. Glycogen is broken down at these nonreducing ends by the enzyme glycogen phosphorylase to release glucose for energy.
  • The primary structural homopolysaccharides are cellulose and chitin. Cellulose, a major component of plant cell walls, is the most abundant natural polymer on Earth.
  • Like α-amylose, cellulose is a linear polysaccharide composed entirely of glucose. However, in cellulose the glucose residues occur in β(1→4) linkage rather than α (1→4) (see Figure 1).
  • In addition, individual cellulose strands can form hydrogen bonds with one another to provide additional strength. Most animals, including humans, lack the enzymes necessary to dissolve α(1→4) linkages and so cannot digest cellulose
  • The animals that can (such as ruminants) do so via a symbiosis with bacteria that secrete cellulose-degrading enzymes.
  • The second most abundant polymer on Earth is chitin. Chitin comprises much of the exoskeletons of crustaceans, insects, and spiders, as well as the cell walls of fungi. Structurally, chitin is very similar to cellulose, except that its basic monosaccharide is N-acetylglucosamine
Becky Kriger

Biopolymers and Bioplastics - 0 views

www.biobasics.gc.ca/...View.asp

shared by Becky Kriger on 08 Dec 08 - Cached
  • Biopolymers are polymers which are present in, or created by, living organisms. These include polymers from renewable resources that can be polymerized to create bioplastics. Bioplastics are plastics manufactured using biopolymers, and are biodegradable.
  • There are two main types of biopolymers: those that come from living organisms; and, those which need to be polymerized but come from renewable resources. Both types are used in the production of bioplastics
  • Biopolymer Natural Source What is it? Cellulose Wood, cotton, corn, wheat, and others This polymer is made up of glucose. It is the main component of plant cell walls. Soy protein Soybeans Protein which naturally occurs in the soy plant. Starch Corn, potatoes, wheat, tapioca, and others This polymer is one way carbohydrates are stored in plant tissue. It is a polymer made up of glucose. It is not found in animal tissues. Polyesters Bacteria These polyesters are created through naturally occurring chemical reactions that are carried out by certain types of bacteria.
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  • Biopolymer Natural Source What is it? Lactic Acid Beets, corn, potatoes, and others Produced through fermentation of sugar feedstocks, such as beets, and by converting starch in corn, potatoes, or other starch sources. It is polymerized to produce polylactic acid -- a polymer that is used to produce plastic. Triglycerides Vegetable oils These form a large part of the storage lipids found in plant and animal cells. Vegetable oils are one possible source of triglycerides that can be polymerized into plastics.
  • Using Fermentation to Produce Plastics Fermentation, used for hundreds of years by humans, is even more powerful when coupled with new biotechnology techniques.
  • Today, fermentation can be carried out with genetically engineered microorganisms, specially designed for the conditions under which fermentation takes place,
  • Fermentation, in fact, is the process by which bacteria can be used to create polyesters. Bacteria called Ralstonia eutropha are used to do this. The bacteria use the sugar of harvested plants, such as corn, to fuel their cellular processes. The by-product of these cellular processes is the polymer.
  • Lactic acid is fermented from sugar, much like the process used to directly manufacture polymers by bacteria. However, in this fermentation process, the final product of fermentation is lactic acid, rather than a polymer. After the lactic acid is produced, it is converted to polylactic acid using traditional polymerization processes.
  • Plants are becoming factories for the production of plastics. Researchers created a Arabidopis thaliana plant through genetic engineering. The plant contains the enzymes used by bacteria to create plastics. Bacteria create the plastic through the conversion of sunlight into energy. The researchers have transferred the gene that codes for this enzyme into the plant, as a result the plant produces plastic through its cellular processes. The plant is harvested and the plastic is extracted from it using a solvent. The liquid resulting from this process is distilled to separate the solvent from the plastic.
  • Currently, fossil fuel is still used as an energy source during the production process. This has raised questions by some regarding how much fossil fuel is actually saved by manufacturing bioplastics. Only a few processes have emerged that actually use less energy in the production process.
  • Energy use is not the only concern when it comes to biopolymers and bioplastics. There are also concerns about how to balance the need to grow plants for food, and the need to grow plants for use as raw materials. Agricultural space needs to be shared. Researchers are looking into creating a plant that can be used for food, but also as feedstock for plastic production.
  • Biopolymers and bioplastics are the main components in creating a sustainable plastics industry. These products reduce the dependence on non-renewable fossil fuels, and are easily biodegradable. Together, this greatly limits the environmental impacts of plastic use and manufacture. Also, characteristics such as being biodegradable make plastics more acceptable for long term use by society. It is likely that in the long term, these products will mean plastics will remain affordable, even as fossil fuel reserves diminish.
Becky Kriger

Plastics - 0 views

nobelprize.org/...readmore.html

shared by Becky Kriger on 08 Dec 08 - Cached
  • lastics are synthetic materials, which means that they are artificial, or manufactured.
  • he building blocks for making plastics are small organic molecules - molecules that contain carbon along with other substances. They generally come from oil (petroleum) or natural gas, but they can also come from other organic materials such as wood fibers, corn, or banana peels! Each of these small molecules is known as a monomer ("one part") because it's capable of joining with other monomers to form very long molecule chains called polymers ("many parts")
  • 1. Crude oil, the unprocessed oil that comes out of the ground, contains hundreds of different hydrocarbons, as well as small amounts of other materials. The job of an oil refinery is to separate these materials and also to break down (or "crack) large hydrocarbons into smaller ones. 2. A petrochemical plant receives refined oil containing the small monomers they need and creates polymers through chemical reactions. 3. A plastics factory buys the end products of a petrochemical plant - polymers in the form of resins - introduces additives to modify or obtain desirable properties, then molds or otherwise forms the final plastic products.
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  • One such molecule is the ethylene monomer, the starting point for a variety of plastics. Ethylene is a small hydrocarbon consisting of four hydrogen atoms and two carbon atoms.
  • Polymerization is often started by combining the monomers through the use of a catalyst - a substance that aids a chemical reaction without undergoing any permanent chemical change itself. During the chemical reaction, hundreds or thousands of monomers combine to form a polymer chain, and millions of polymer chains are formed at the same time. The mass of polymers that results is known as a resin.
  • Polyethylene is made from just ethylene monomers - but it's also possible to create polymers from two or more different monomers. You can make hundreds of different polymers depending on which monomers and catalysts you use.
  • Cellulose, the basic component of plant cell walls is a polymer, and so are all the proteins produced in your body and the proteins you eat. Another famous example of a polymer is DNA - the long molecule in the nuclei of your cells that carries all the genetic information about you.
  • lastics are classified into two categories according to what happens to them when they're heated to high temperatures. Thermoplastics keep their plastic properties: They melt when heated, then harden again when cooled. Thermosets, on the other hand, are permanently "set" once they're initially formed and can't be melted. If they're exposed to enough heat, they'll crack or become charred.
  • Thermoplastics have long, linear polymer chains that are only weakly chemically bonded, or connected, to each other. When a thermoplastic object is heated, these bonds are easily broken, which makes the polymers able to glide past each other like strands of freshly cooked spaghetti. That's why thermoplastics can readily be remolded. The weak bonds between the polymers reform when the plastic object is cooled, which enable it to keep its new shape.
  • The linear chains are crosslinked - strongly chemically bonded. This prevents a thermoplastic object from being melted and reformed.
  • The most common method for making plastics is molding. To make a thermoplastic object, plastic granules known as resin are forced into a mold under high heat and pressure. When the material has cooled down, the mold is opened and the plastic object is complete. When making plastic fibers, the molten resin is sprayed through a strainer with tiny holes.
  • Thermosets are produced in two steps: 1. Linear polymers are formed. 2. The linear polymers are forced into a mold where "curing" takes place. This may involve heating, pressure, and the addition of catalysts. During this process, a cross-linked or networked structure forms, creating a permanently hard object that is no longer meltable or moldable.
  • For most applications, the ideal polymer is a long, straight chain with a highly regular molecular structure. Early synthetic polymers, however, often exhibited odd little branches and other irregularities. In the 1950s, German chemist Karl Ziegler (1898–1973) discovered that an entirely different type of catalyst - a combination of aluminum compounds with other metallic compounds - could solve some of these annoying problems and increase the length of a polymer chain, producing superior plastics.
  • olymers often have short side chains, which can occur on either side of the main chain. If side branches occur randomly to the left or right, the polymer has an irregular structure. Italian chemist Giulio Natta (1903–1979) discovered that some Ziegler catalysts led to a uniform structure in which all the side branches are on the same side.
  • Firstly, there is an environmental impact from plastics production; however the plastics industry has worked hard to reduce energy and water use, as well as waste generation during the manufacturing processes.
  • Secondly, during their lives, plastic products can save energy and reduce carbon dioxide emissions in a variety of ways. For example, they're lightweight, so transporting them is energy efficient. And plastic parts in cars and airplanes reduce the weight of those vehicles and therefore less energy is needed to operate them and lower emissions are created.
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