10.1 Carbs Structure

2. Write a general formula to show the chemical composition of carbohydrates.

(CH2O)n

9) Distinguish between furanoses and pyranoses, and between α- and β-anomers.

-Pyranose is more stable than Furanose. -Anomers differ about the anomeric (Carbonyl) carbon. α or β.

1. Name three major functions of carbohydrates.

1) Cellular fuel: Oxidation of CHO(carbohydrate) is primary energy source for most non-photosynthetic cells 2)Structural and protective elements: bacterial and plant cell walls and connective tissue in animals 3) glycoconjugates (glycolipids, glycoproteins, proteoglycans) -Lubrication of skeletal joints in higher animals -Cell recognition and adhesion molecules. -Covalently attach to protein and lipid and act as signal molecules.

4. List and describe 4 ways to classify monosaccharides.

1- Monosaccharides -simple sugars 2- Disaccharides 3- Oligosaccharides - three (disaccharides) to 20 monosaccharides joined by glycosidic bonds. 4-Polysaccharides-20 or more (100s to 1000s) -Linear or branched chains

20) Name two amino acids, which commonly form linkages with carbohydrates.

Carbohydrates are typically attached (covalently) to proteins via Ser/Thr (o-linked) or Asn (n-linked).

16) Name two tissues, which contain glycogen granules.

Glycogen is especially abundant in the liver, where it may constitute as much as 7% of the wet weight; it is also present in skeletal muscle.

11) Define reducing sugar, and be able to distinguish between a reducing sugar and a non-reducing sugar.

Monosaccharides can be oxidized by relatively mild oxidizing agents such as ferric (Fe3+) or cupric (Cu2+) ion (Fig. 11-10). The carbonyl carbon is oxidized to a carboxylic acid. Glucose and other sugars capable of reducing ferric or cupric ion are called reducing sugars. This property is useful in the analysis of sugars; it is the basis of Fehling's reaction (Fig. 11-l0a), a qualitative test for the presence of reducing sugar. By measuring the amount of oxidizing agent that is reduced by a solution of a sugar, it is also possible to estimate the concentration of that sugar. For many years, the glucose content of blood and urine was determined in this way in the diagnosis of diabetes mellitus, a disease in which the blood glucose level is abnormally high and there is excessive urinary excretion of glucose. Now, more sensitive methods for measuring blood glucose employ an enzyme, glucose oxidase • -Aldehyde(outskirts of the carbon chains) groups are reducing (e- donating)...ketones(inside the chain) are not • Pyranosides are reducing (produce aldose in open chain) • Furnaosides are non-reducing (produce ketose in open chain*) Basically at C1' you will have an OH group present!

10) Describe mutarotation.

Interconversion is called mutarotation. Mutarotation is the change in the optical rotation because of the change in the equilibrium between two anomers, when the corresponding stereocenters interconvert. Cyclic sugars show mutarotation as α and β anomeric forms interconvert.

14) Define oligosaccharide, homopolysaccharide and heteropolysaccharide (usually glycosaminoglycans or mucopolysaccarides) .

Most of the carbohydrates found in nature occur as polysaccharides, polymers of high molecular weight. Polysaccharides, also called glycans, differ from each other in the identity of their recurring monosaccharide units, in the length of their chains, in the types of bonds linking the units, and in the degree of branching. Homopolysaccharides contain only a single type of monomeric unit; heteropolysaccharides contain two or more different kinds of monomeric units (Fig. 11-13). Some homopolysaccharides serve as storage forms of monosaccharides used as fuels; starch and glycogen are homopolysaccharides of this type. Other homopolysaccharides (cellulose and chitin, for example) serve as structural elements in plant cell walls and animal exoskeletons. Heteropolysaccharides provide extracellular support for organisms of all kingdoms. The rigid layer of the bacterial cell envelope (the peptidoglycan) is a heteropolysaccharide built from two alternating monosaccharide units. In animal tissues, the extracellular space is occupied by several types of heteropolysaccharides, which form a matrix that holds individual cells together and provides protection, shape, and support to cells, tissues, or organs. Hyaluronic acid, one of the polymers that accounts for the toughness and flexibility of cartilage and tendon, typifies this group of extracellular polysaccharides. Other heteropolysaccharides, sometimes in very large aggregates with proteins (proteoglycans), account for the high viscosity and lubricating properties of some extracellular secretions.

5. Epimers

When two sugars differ only in the configuration around one carbon atom, they are called epimers of each other; D-glucose and D-mannose, which differ only in the stereochemistry at C-2, are epimers, as are D-glucose and D-galactose. Some sugars do occur naturally in their L form; examples are L-arabinose and the L isomers of some sugar derivatives that are common components of glycoproteins.

6) Appreciate the differences in the structures of the various 3-6 carbon ALDOSES.

3-> D- Glyceraldehyde 4-> D- Erytherose 5-> D- Ribose D- Xylose D- Arabinose 6-> D- Glucose D- Mannose D- Galactose

6) Appreciate the differences in the structures of the various 3-6 carbon KETOSES.

3-> Dihydroxyacetone 5-> D- Ribulose 6-> D- Fructose

15. Amylose & Amylopectin

Amylose and amylopectin, the polysaccharides of starch. (a) Amylose, a linear(unbranched) polymer of D-glucose units in (α1→4) linkage. Each polymer chain can contain several thousand glucose residues. (b) Amylopectin. Each hexagon represents one glucose residue. The colored hexagons represent residues of the outer branches, which are removed enzymatically one at a time during the intracellular mobilization of starch for energy production. This diagram shows only a very small portion of a very long molecule. Glycogen has a similar structure but is more highly branched and more compact. (c) Structure of an (α1→6) branch point. During starch breakdown, a separate enzyme is required to break the (α1→6) linkage.

11) Define reducing sugar, and be able to distinguish between a reducing sugar and a non-reducing sugar. Part B.

Fructose is a ketohexose and therefore should NOT be a reducing sugar. However, fructose is subject to tautomerism which rearranges the ketone to an aldehyde and fructose will act as a reducing sugar. Sucrose and trehalose are NOT reducing sugars as the anomeric carbon is contained in the o-glycosidic link and therefore cannot assume ANY open chain configurations to provide the aldehyde reducing group -Aldehyde is the one that reduced them boys, so usually fructose wouldn't be it but the tautomerism causes a change leading it to have an aldehyde so it can be a reducing sugar. ---So a reducing sugar possess a free aldehyde(-CHO) or ketone (-C=0) group.

17) Discuss the reasons for glucose storage as glycogen rather than free glucose.

Glycogen is the main storage polysaccharide of animal cells. Like amylopectin, glycogen is a polymer of (α1→4)-linked subunits of glucose, with (α1→6)-linked branches, but glycogen is more extensively branched (branches occur every 8 to 12 residues) and more compact than starch. Glycogen is especially abundant in the liver, where it may constitute as much as 7% of the wet weight; it is also present in skeletal muscle. In hepatocytes glycogen is found in large granules (Fig. 11-14), which are themselves clusters of smaller granules composed of single, highly branched glycogen molecules with an average molecular weight of several million. Such glycogen granules also contain, in tightly bound form, the enzymes responsible for the synthesis and degradation of glycogen. Because each branch in starch (Fig. 11-15b) and glycogen ends with a nonreducing sugar (one without a free anomeric carbon), these polymers have as many nonreducing ends as they have branches, but only one reducing end. When starch or glycogen is used as an energy source, glucose units are removed one at a time from the nonreducing ends. Because of the branching of amylopectin and glycogen, degradative enzymes (which act at nonreducing ends) can work simultaneously at many ends, speeding the conversion of the polymer to monosaccharides.

9. α- and β-anomers

In aqueous solution, we have 33% -D-glucopyranose (α=axial -OH). But we have 67% -D-glucopyranose (because is sterically favorable; equatorial OH) (β=equatorial -OH) Beta is like Beta sit down and the newly formed OH group is on the same side as CH2OH while with Alpha it is on the opposite side. Beta is when OH as well as CH2OH which is the bulkiest group is in equatorial position!

5. Stereoisomer Formula(Chiral Centers)

In general, a molecule with n chiral centers can have 2n stereoisomers. Glyceraldehyde has 21 = 2; the aldohexoses, with four chiral centers, have 24 = 16 stereoisomers. The stereoisomers of monosaccharides of each carbon chain length can be divided into two groups, which differ in the configuration about the chiral center most distant from the carbonyl carbon; those with the same configuration at this reference carbon as that of D-glyceraldehyde are designated D isomers, and those with the configuration of L-glyceraldehyde are L. isomers. When the hydroxyl group on the reference carbon is on the right in the projection formula, the sugar is the D isomer; when on the left, the L isomer. Of the 16 possible aldohexoses, 8 are D forms and 8 are L. Most of the hexoses found in living organisms are D isomers.

13) Distinguish between maltose, lactose, sucrose, and trehalose with respect to the types of monosaccharide units and linkages present.

Maltose is alpha, beta of reducing sugars. Lactose is beta, beta reducing sugars. Sucrose is alpha, beta non-reducing sugars. Trehalose is alpha, alpha non-reducing sugars. Other reducing sugars are the aldehyde ones like fructose, glucose, maltose, galactose, lactose Other non-reducing sugars are sucrose, trehalose cuz both of these do not have an OH group present on the anomeric carbons aka C1'!!!

3. Discuss the properties of carbohydrates with respect to polarity and water solubility.

Monosaccharides are colorless, crystalline solids that are freely soluble in water but insoluble in nonpolar solvents. Most have a sweet taste. The backbone of monosaccharides is an unbranched carbon chain in which all the carbon atoms are linked by single bonds. One of the carbon atoms is double-bonded to an oxygen atom to form a carbonyl group; each of the other carbon atoms has a hydroxyl group. If the carbonyl group is at an end of the carbon chain, the monosaccharide is an aldehyde and is called an aldose; if the carbonyl group is at any other position, the monosaccharide is a ketone and is called a ketose. The simplest monosaccharides are the two three-carbon trioses: glyceraldehyde, an aldose, and dihydroxyacetone, a ketose.

5. Recognize D and L stereoisomers.

Saccharides have multiple chiral centers: D/L designation based on chiral carbon most distant from the carbonyl(CHO) carbon. All the monosaccharides except dihydroxyacetone contain one or more asymmetric (chiral) carbon atoms and thus occur in optically active isomeric forms (Chapter 3). The simplest aldose, glyceraldehyde, contains a chiral center (the middle carbon atom) and therefore has two different optical isomers, or enantiomers (Fig. 11-2; see also Fig. 3-9). By convention, one of these two forms is designated the D isomer of glyceraldehyde; the other is the L isomer. To represent three-dimensional sugar structures on paper, we often use Fischer projection formulas (Fig. 11-2). SnL go together!!!

15) Compare starch, amylose, amylopectin, glycogen, cellulose, and chitin with respect to their structures (monosaccharide units and linkages), locations in nature, functions, properties (branched vs. helical), and modes of digestion (names of enzymes with specificities).

The most important storage polysaccharides in nature are starch in plant cells and glycogen in animal cells. Both polysaccharides occur intracellularly as large clusters or granules (Fig. 11-14). Starch and glycogen molecules are heavily hydrated because they have many exposed hydroxyl groups available to hydrogen bond with water. Most plant cells have the ability to form starch, but it is especially abundant in tubers, such as potatoes, and in seeds, such as corn. Starch contains two types of glucose polymer, amylose and amylopectin. The former consists of long, unbranched chains of D-glucose units connected by (α1→4) linkages (Fig. 11-15a). Such chains vary in molecular weight from a few thousand to 500,000. Amylopectin also has a high molecular weight (up to 1 million) but is highly branched (Fig. 11-15b). The glycosidic linkages joining successive glucose residues in amylopectin chains are (α1→4), but the branch points, occurring every 24 to 30 residues, are (α1→6) linkages to make the amylopectin a very highly branched structure so that it can do more things! (Fig. 11-15c).

8) Discuss the planarity of monosaccharides.

The six-membered pyranose ring is not planar, because of the tetrahedral geometry of its saturated carbon atoms. Instead, pyranose rings adopt two classes of conformations, termed chair and boat because of the resemblance to these objects (Figure 11.7). In the chair form, the substituents on the ring carbon atoms have two orientations: axialand equatorial. Axial bonds are nearly perpendicular to the average plane of the ring, whereas equatorial bonds are nearly parallel to this plane. Axial substituents sterically hinder each other if they emerge on the same side of the ring (e.g., 1,3-diaxial groups). In contrast, equatorial substituents are less crowded. The chair form of β-D-glucopyranose predominates because all axial positions are occupied by hydrogen atoms. The bulkier -OH and -CH2OH groups emerge at the less-hindered periphery. The boat form of glucose is disfavored because it is quite sterically hindered.

17. cont.d

Why not store glucose in its monomeric form? Liver and skeletal muscle contain glycogen equivalent to several percent of their wet weight, in an essentially insoluble form that contributes very little to the osmotic strength of the cytosol. If the cytosol were a 2% glucose solution (about 0.1 M), the osmolarity of the cell would be threateningly elevated. Furthermore, with an intracellular glucose concentration of 0.1 M and an external concentration of about 5 mM (in a mammal), the free-energy change for glucose uptake would be prohibitively large.

7) Convert a straight chain carbohydrate (Fischer projection) to a cyclic form (Haworth projection).

With a 5 carbon chain your fischer projections turn into a furanose. With a 6 carbon chain your fischer projections turn into a pyranose.