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Concentration Gradient; Within a System, Different Substances in the Medium Will Each Diffuse at Different Rates According to Their Individual Gradients

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Concentration Gradient; Within a System, Different Substances in the Medium Will Each Diffuse at Different Rates According to Their Individual Gradients Biomolecules Biological Macromolecules • Life depends on four types of organic macromolecules: 1. Carbohydrates 2. Lipids 3. Proteins 4. Nucleic acids 1. Carbohydrates • Contain carbon, hydrogen and oxygen in a ratio of 1:2:1 • Account for less that 1% of body weight • Used as energy source • Called saccharides Carbohydrates • Compounds containing C, H and O • General formula : Cx(H2O)y • All have C=O and -OH functional groups. • Classified based on • Size of base carbon chain • Number of sugarunits • Location of C=O • Stereochemistry Types of carbohydrates • Classifications based on number of sugarunits in total chain. • Monosaccharides - single sugarunit • Disaccharides - two sugarunits • Oligosaccharides - 2 to 10 sugarunits • Polysaccharides - more than 10units • Chaining relies on ‘bridging’ of oxygenatoms • glycoside bonds Monosaccharides • Based on location of C=O H CH2OH | | C=O C=O | | H-C-OH HO-C-H | | H-C-OH H-C-OH | | H-C-OH H-C-OH | | CH2OH CH2OH Aldose Ketose - aldehyde C=O - ketone C=O Monosaccharide classifications • Number of carbon atoms in the chain H H | H | C=O H | C=O | | C=O | H-C-OH C=O | H-C-OH | | H-C-OH | H-C-OH | H-C-OH | H-C-OH H-C-OH | H-C-OH | | H-C-OH | CH2OH | H-C-OH CH2OH | CH2OH CH2OH triose tetrose pentose hexose Can be either aldose or ketose sugar. Stereoisomers • Stereochemistry • Study of the spatial arrangement ofmolecules. • Stereoisomers have • the same order and types of bonds. • different spatial arrangements. • different properties. • Many biologically importantchemicals, like sugars, exist as stereoisomers. Your body can tell the difference. Chiral center Asymmetric carbon - 4 different things are attached to it. • Cl • | • I - C - F • | • Br Chiral center • You must have at least one asymmetric carbon to havestereoisomers Some important monosaccharides • D-glyceraldehyde Simplest sugar • D-glucose Most important indiet • D-fructose Sweetest of allsugars • D-galactose Part of milk sugar • D-ribose Used in RNA • note that each is a D-enantiomer Hemiacetal & hemiketal formation H H An aldehyde can C O react with an + R' OH R' O C OH alcohol to form R R a hemiacetal. aldehyde alcohol hemiacetal A ketone can R R react with an C O + "R OH "R O C OH alcohol to form R' R' a hemiketal. ketone alcohol hemiketal Pentoses and 1CHO H C OH hexoses can cyclize 2 as the ketone or HO C H 3 D-glucose aldehyde reacts H C OH (linear form) with a distalOH. 4 H C OH Glucose forms an 5 CH OH intra-molecular 6 2 hemiacetal, as the 6CH2OH 6 CH2OH C1aldehyde & C5 5 5 H O H H O OH OHreact, to form H H a 6-member 4 OH H 1 4 OH H 1 pyranose ring, OH OH OH H 3 2 3 2 named after pyran. H OH H OH -D-glucose -D-glucose These representations of the cyclic sugars are called Haworth projections. 6CH2OH 6 CH2OH 5 5 H O H H O OH H H 4 OH H 1 4 OH H 1 OH OH OH H 3 2 3 2 H OH H OH -D-glucose -D-glucose Cyclization of glucose produces a new asymmetriccenter at C1. The 2 stereoisomers are called anomers, & . Haworth projections represent the cyclic sugars ashaving essentially planar rings, with the OH at theanomeric C1: (OH below the ring) (OH above the ring). Monosaccharides can be oxidized by relatively mild oxidizing agents such as ferric (Fe3+) or cupric (Cu2+) ion . The carbonyl carbon is oxidized to a carboxyl group. Glucose and other sugars capable of reducing ferric or cupric ion are called reducing sugars. Glycosidic Bonds The anomeric hydroxyl and a hydroxyl of another sugar or some other compound can join together, splitting out water to forma glycosidic bond: R-OH + HO-R' R-O-R' + H2O E.g., methanol reacts with the anomeric OH onglucose to form methylglucoside (methyl-glucopyranose). H OH H OH H O H2O H O HO HO HO H + CH3-OH HO H H OH H OH H OH H OCH3 -D-glucopyranose methanol methyl--D-glucopyranose Glycoside formation • or -OH group of cyclicmonosaccharide can form link with another one (ormore). CH2OH CH2OH H O OH H O H H H • glycosidic bond OH H H OH OH H OH OH H OH OH H • sugar -O- sugar CH2OH CH2OH H O H O H H H OH H o OH H OH • oxygen bridge OH H OH H H OH + H2 O Types Of (O-Glycosidic) Bonding In O-Glycosidic Bonding There are Two Types of Linkages 1) Alpha Linkage 2) Beta Linkage • Maltose is a disaccharide, formed by two glucose units. It occurs in cells as a breakdown product of starch. It is also formed in the seeds during germination. It is commonly called malt sugar. • The glycosidic bond of maltoseis formed between the OH of carbon 1 and carbon 4 of 2 glucose monomers. Therefore it forms an alpha (1–> 4) glycosidic bond. Lactose is a disaccharide found in milk and hence commonly called milk sugar. It is formed by condensation of a glucose molecule and a galactose molecule. composed of a glucose and a galactose monomer. They form a beta (1–> 4) glycosidic bond. Sucrose is disaccharide found extensively in plants. It is commonly called cane sugar. It is formed by a condensation of a molecule of glucose and a molecule of fructose. Sucrose links the anomeric hydroxyls of glucose and fructose to form an alpha (1–>2) glycosidic bond. Cellulose The most abundant natural polymer found in the world. Found in the cell wall of almost all plants, it provides physical structure and strength. Cellulose is a straight chain polysaccharide with beta (1–>4) linkages. STARCH Amylose is a straight chain with alpha (1–>4) linkages Amylopectin is an alpha (1–>4) chain with alpha (1–>6) . Reference books:- 1. Campbell, MK (2012) Biochemistry, 7th ed., Published by Cengage Learning. 2. Campbell, PN and Smith AD (2011) Biochemistry Illustrated, 4th ed., Published by Churchill Livingstone. 3. Tymoczko JL, Berg JM and Stryer L (2012) Biochemistry: A short course, 2nd ed., W.H.Freeman. 4. Berg JM, Tymoczko JL and Stryer L (2011) Biochemistry, W.H.Freeman and Company. 5. Nelson DL and Cox MM (2008) Lehninger Principles of Biochemistry, 5th Edition., W.H. Freeman 6. Willey MJ, Sherwood, LM & Woolverton C J (2013) Prescott, Harley and Klein’s Microbiology by. 9th Ed., McGrawHill. 7. Voet,D. and Voet J.G (2004) Biochemistry 3rd edition, John Wiley and Sons. Carbohydrate Representations Based on a Fall 2005 Chemistry 14D honors project Some Useful Vocabulary: Aldose: A polyhydroxy aldehyde, i.e., a carbohydrate containing an aldehyde functional group. Ketose: A polyhydroxy ketone, i.e., a carbohydrate containing a ketone functional group. Furanose: A five-member closed chain form of a monosaccharide. Pyranose: A six-member cyclic form of a monosaccharide. Fischer Projection: A way of representing an acyclic (open chain) carbohydrate structure. Vertical lines point away from the viewer and horizontal lines point toward the viewer. Haworth Projection: A way of representing a cyclic (closed chain) carbohydrate. Substituents can either point up or down on this ring. Chair Conformation: The most stable conformation of cyclohexane that resembles a chair. Monosaccharide: A single sugar. A carbohydrate that cannot be broken down into a simpler carbohydrate. Anomeric carbon: The carbon in a cyclic sugar that is the carbonyl carbon in the open- chain (acyclic) form. Carbohydrates are the most abundant class of bioorganic compounds in the biological world. They constitute most of Earth’s biomass, from tiny structural components of cells, to food we eat for metabolic energy. To better understand the role carbohydrates play in the biological world, a basic chemical understanding of how carbohydrates are formed and represented in their simplest form is essential. In organic chemistry, monosaccharides, the simplest carbohydrates are represented in three ways: the Fischer projection, Haworth projection, and the chair conformation of D-glucose (Figure 1). By the time you are finished reading this tutorial, you will have learned how to represent monosaccharides in these three ways. Figure 1 Monosaccharides, also known as saccharides, are carbohydrates that cannot be broken down into simpler carbohydrates. They can be polyhydroxy aldehydes or polyhydroxy ketones because they have either an aldehyde or a ketone group, along with –OH substituted carbons in a chain. Polyhydroxy aldehydes are called aldoses. Polyhydroxy ketones are called ketoses. The suffix “ose” means sugar, while the prefixes “ald” and “ket” are used for aldehyde and ketone, respectively. Classification of monosaccharides is based on the number of carbons they contain (Table 1). Table 1 Number of Name Aldose Form Ketose Form carbons in monosaccharide 3 Triose aldotriose ketotriose 4 Tetrose aldotetrose ketotetrose Tutorial: Carbohydrate Representations 2 5 Pentose aldopentose ketopentose 6 Hexose aldohexose ketohexose Monosaccharides can exist in an open chain (acyclic) form, or in closed chain (cyclic) form. The open chain form of monosaccharides is illustrated with Fischer projections. A Haworth projection can be used to represent the cyclic form of monosaccharides. The five-member closed chain form of a monosaccharide is known as a furanose, while the six-member cyclic form of a monosaccharide is known as a pyranose. Often six-member monosaccharide rings can also be represented in chair conformation. Figure 2 shows pyranose and furanose rings. Substituents have been omitted so that the ring structure can be emphasized. Figure 2 Imagine we are asked to show the Fischer, Haworth, and chair conformation of _ and _ D-glucose. How do we go about doing this? There are many things to consider; however, there are also some rules that will simplify the process.
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