1. Biochemistry
Lecture 7

2. FIGURE 7-1a Representative monosaccharides
FIGURE 7-1a Representative monosaccharides. (a)Two trioses, an aldose and a ketose. The carbonyl group in each is shaded.

3. Enantiomers
FIGURE 7-2 (part 1) Three ways to represent the two enantiomers of glyceraldehyde. The enantiomers are mirror images of each other. Ball-and-stick models show the actual configuration of molecules. Recall (see Figure 1-17) that in perspective formulas, solid wedge-shaped bonds point toward the reader, dashed wedges point away.

4. Drawing Monosaccharides
Chiral compounds can be drawn using perspective formulas
However, chiral carbohydrates are usually represented by Fischer projections
Horizontal bonds are pointing towards you; vertical bonds are projecting away from you

5. FIGURE 7-2 (part 3) Three ways to represent the two enantiomers of glyceraldehyde. The enantiomers are mirror images of each other. Ball-and-stick models show the actual configuration of molecules. Recall (see Figure 1-17) that in perspective formulas, solid wedge-shaped bonds point toward the reader, dashed wedges point away.

6. FIGURE 7-2 (part 2) Three ways to represent the two enantiomers of glyceraldehyde. The enantiomers are mirror images of each other. Ball-and-stick models show the actual configuration of molecules. Recall (see Figure 1-17) that in perspective formulas, solid wedge-shaped bonds point toward the reader, dashed wedges point away.

7. Epimers
FIGURE 7-4 Epimers. D-Glucose and two of its epimers are shown as projection formulas. Each epimer differs from D-glucose in the configuration at one chiral center (shaded pink).

8. FIGURE 7-3a (part 1) Aldoses and ketoses
FIGURE 7-3a (part 1) Aldoses and ketoses. The series of (a) D-aldoses and (b) D-ketoses having from three to six carbon atoms, shown as projection formulas. The carbon atoms in red are chiral centers. In all these D isomers, the chiral carbon most distant from the carbonyl carbon has the same configuration as the chiral carbon in D-glyceraldehyde. The sugars named in boxes are the most common in nature; you will encounter these again in this and later chapters.

9. FIGURE 7-3a (part 2) Aldoses and ketoses
FIGURE 7-3a (part 2) Aldoses and ketoses. The series of (a) D-aldoses and (b) D-ketoses having from three to six carbon atoms, shown as projection formulas. The carbon atoms in red are chiral centers. In all these D isomers, the chiral carbon most distant from the carbonyl carbon has the same configuration as the chiral carbon in D-glyceraldehyde. The sugars named in boxes are the most common in nature; you will encounter these again in this and later chapters.

10. FIGURE 7-3a (part 3) Aldoses and ketoses
FIGURE 7-3a (part 3) Aldoses and ketoses. The series of (a) D-aldoses and (b) D-ketoses having from three to six carbon atoms, shown as projection formulas. The carbon atoms in red are chiral centers. In all these D isomers, the chiral carbon most distant from the carbonyl carbon has the same configuration as the chiral carbon in D-glyceraldehyde. The sugars named in boxes are the most common in nature; you will encounter these again in this and later chapters.

11. FIGURE 7-3b (part 1) Aldoses and ketoses
FIGURE 7-3b (part 1) Aldoses and ketoses. The series of (a) D-aldoses and (b) D-ketoses having from three to six carbon atoms, shown as projection formulas. The carbon atoms in red are chiral centers. In all these D isomers, the chiral carbon most distant from the carbonyl carbon has the same configuration as the chiral carbon in D-glyceraldehyde. The sugars named in boxes are the most common in nature; you will encounter these again in this and later chapters.

12. FIGURE 7-3b (part 2) Aldoses and ketoses
FIGURE 7-3b (part 2) Aldoses and ketoses. The series of (a) D-aldoses and (b) D-ketoses having from three to six carbon atoms, shown as projection formulas. The carbon atoms in red are chiral centers. In all these D isomers, the chiral carbon most distant from the carbonyl carbon has the same configuration as the chiral carbon in D-glyceraldehyde. The sugars named in boxes are the most common in nature; you will encounter these again in this and later chapters.

13. Hemiacetals and Hemiketals
FIGURE 7-5 Formation of hemiacetals and hemiketals. An aldehyde or ketone can react with an alcohol in a 1:1 ratio to yield a hemiacetal or hemiketal, respectively, creating a new chiral center at the carbonyl carbon. Substitution of a second alcohol molecule produces an acetal or ketal. When the second alcohol is part of another sugar molecule, the bond produced is a glycosidic bond (p. 243).

14. Cyclization
FIGURE 7-6 Formation of the two cyclic forms of D-glucose. Reaction between the aldehyde group at C-1 and the hydroxyl group at C-5 forms a hemiacetal linkage, producing either of two stereoisomers, the α and β anomers, which differ only in the stereochemistry around the hemiacetal carbon. The interconversion of α and β anomers is called mutarotation.

15. Pyranoses and Furanoses
FIGURE 7-7 Pyranoses and furanoses. The pyranose forms of D-glucose and the furanose forms of D-fructose are shown here as Haworth perspective formulas. The edges of the ring nearest the reader are represented by bold lines. Hydroxyl groups below the plane of the ring in these Haworth perspectives would appear at the right side of a Fischer projection (compare with Figure 7-6). Pyran and furan are shown for comparison.

16. Chain-ring Equilibrium and Reducing Sugars
FIGURE 7-10 Sugars as reducing agents. Oxidation of the anomeric carbon (and probably the neighboring carbon) of glucose and other sugars under alkaline conditions is the basis for Fehling's reaction. The cuprous ion (Cu+) produced forms a red cuprous oxide precipitate. In the hemiacetal (ring) form, C-1 of glucose cannot be oxidized by complexed Cu2+. However, the open-chain form is in equilibrium with the ring form, and eventually the oxidation reaction goes to completion. The reaction with Cu2+ is complex, yielding a mixture of products and reducing 3 mol of Cu2+ per mole of glucose.

17. Colorimetric Glucose Analysis

18. Polymers of Carbohydrates

19. The Glycosidic Bond
FIGURE 7-11 Formation of maltose. A disaccharide is formed from two monosaccharides (here, two molecules of D-glucose) when an —OH (alcohol) of one glucose molecule (right) condenses with the intramolecular hemiacetal of the other glucose molecule (left), with elimination of H2O and formation of a glycosidic bond. The reversal of this reaction is hydrolysis—attack by H2O on the glycosidic bond. The maltose molecule, shown here as an illustration, retains a reducing hemiacetal at the C-1 not involved in the glycosidic bond. Because mutarotation interconverts the α and β forms of the hemiacetal, the bonds at this position are sometimes depicted with wavy lines, as shown here, to indicate that the structure may be either α or β.

20. Nonreducing disaccharides
FIGURE 7-12 Some common disaccharides. Like maltose in Figure 7-11, these are shown as Haworth perspectives. The common name, full systematic name, and abbreviation are given for each disaccharide. Formal nomenclature for sucrose names glucose as the parent glycoside, although it is typically depicted as shown, with glucose on the left.

21. FIGURE 7-13 Homo- and heteropolysaccharides
FIGURE 7-13 Homo- and heteropolysaccharides. Polysaccharides may be composed of one, two, or several different monosaccharides, in straight or branched chains of varying length.

22. Glycogen
FIGURE 7-14b Glycogen and starch. (b) An (α1→6) branch point of glycogen or amylopectin.

23. Starch
FIGURE 7-14a Glycogen and starch. (a) A short segment of amylose, a linear polymer of D-glucose residues in (α1→4) linkage. A single chain can contain several thousand glucose residues. Amylopectin has stretches of similarly linked residues between branch points. Glycogen has the same basic structure, but has more branching than amylopectin.

24. Cellulose
FIGURE 7-15a Cellulose. (a) Two units of a cellulose chain; the D-glucose residues are in (β1→4) linkage. The rigid chair structures can rotate relative to one another.

25. Other Polymers
Agar
Chitin
Heparin

26. Glycoconjugates: Glycoproteins
FIGURE 7-17 Chitin. (b) A spotted June beetle (Pelidnota punctata), showing its surface armor (exoskeleton) of chitin.

27. FIGURE 7-35 Roles of oligosaccharides in recognition and adhesion at the cell surface. (a) Oligosaccharides with unique structures (represented as strings of hexagons), components of a variety of glycoproteins or glycolipids on the outer surface of plasma membranes, interact with high specificity and affinity with lectins in the extracellular milieu. (b) Viruses that infect animal cells, such as the influenza virus, bind to cell surface glycoproteins as the first step in infection. (c) Bacterial toxins, such as the cholera and pertussis toxins, bind to a surface glycolipid before entering a cell. (d) Some bacteria, such as H. pylori, adhere to and then colonize or infect animal cells. (e) Selectins (lectins) in the plasma membrane of certain cells mediate cell-cell interactions, such as those of neutrophils with the endothelial cells of the capillary wall at an infection site. (f) The mannose 6-phosphate receptor/lectin of the trans Golgi complex binds to the oligosaccharide of lysosomal enzymes, targeting them for transfer into the lysosome.

29. Lipids

30. FIGURE 10-9 (part 1) Glycerophospholipids
FIGURE 10-9 (part 1) Glycerophospholipids. The common glycerophospholipids are diacylglycerols linked to head-group alcohols through a phosphodiester bond. Phosphatidic acid, a phosphomonoester, is the parent compound. Each derivative is named for the head-group alcohol (X), with the prefix "phosphatidyl-." In cardiolipin, two phosphatidic acids share a single glycerol (R1 and R2 are fatty acyl groups).

31. FIGURE 10-23 Lipids as pigments in plants and bird feathers
FIGURE Lipids as pigments in plants and bird feathers. Compounds with long conjugated systems absorb light in the visible region of the spectrum. Subtle differences in the chemistry of these compounds produce pigments of strikingly different colors. Birds acquire the pigments that color their feathers red or yellow by eating plant materials that contain carotenoid pigments, such as canthaxanthin and zeaxanthin. The differences in pigmentation between male and female birds are the result of differences in intestinal uptake and processing of carotenoids.

32. Classification of lipids
FIGURE 10-7 Some common types of storage and membrane lipids. All the lipid types shown here have either glycerol or sphingosine as the backbone (pink screen), to which are attached one or more long-chain alkyl groups (yellow) and a polar head group (blue). In triacylglycerols, glycerophospholipids, galactolipids, and sulfolipids, the alkyl groups are fatty acids in ester linkage. Sphingolipids contain a single fatty acid, in amide linkage to the sphingosine backbone. The membrane lipids of archaea are variable; that shown here has two very long, branched alkyl chains, each end in ether linkage with a glycerol moiety. In phospholipids the polar head group is joined through a phosphodiester, whereas glycolipids have a direct glycosidic linkage between the head-group sugar and the backbone glycerol.

33. Fatty Acids
Carboxylic acids with hydrocarbon chains containing from 4 to 36 carbons
Almost all natural fatty acids have an even number of carbons
Most natural fatty acids are unbranched
Saturated: no double bonds between carbons in the chain
Monounsaturated: one double bond between carbons in the alkyl chain
Polyunsaturated: more than one double bond in the alkyl chain

34. FIGURE 10-1 Two conventions for naming fatty acids
FIGURE 10-1 Two conventions for naming fatty acids. (a) Standard nomenclature assigns the number 1 to the carboxyl carbon (C-1), and α to the carbon next to it. The position of any double bond(s) is indicated by Δ followed by a superscript number indicating the lower-numbered carbon in the double bond. (b) For polyunsaturated fatty acids (PUFAs), an alternative convention numbers the carbons in the opposite direction, assigning the number 1 to the methyl carbon at the other end of the chain; this carbon is also designated ω (omega; the last letter in the Greek alphabet). The positions of the double bonds are indicated relative to the ω carbon.

36. Conformation of Fatty Acids
FIGURE 10-2ab The packing of fatty acids into stable aggregates. The extent of packing depends on the degree of saturation. (a) Two representations of the fully saturated acid stearic acid, 18:0 (stearate at pH 7), in its usual extended conformation. Each line segment of the zigzag represents a single bond between adjacent carbons. (b) The cis double bond (shaded) in oleic acid, 18:1(Δ9) (oleate), restricts rotation and introduces a rigid bend in the hydrocarbon tail. All other bonds in the chain are free to rotate.

37. FIGURE 10-2cd The packing of fatty acids into stable aggregates
FIGURE 10-2cd The packing of fatty acids into stable aggregates. The extent of packing depends on the degree of saturation. (c) Fully saturated fatty acids in the extended form pack into nearly crystalline arrays, stabilized by many hydrophobic interactions. (d) The presence of one or more fatty acids with cis double bonds interferes with this tight packing and results in less stable aggregates.

38. Triacylglycerols
FIGURE 10-3 Glycerol and a triacylglycerol. The mixed triacylglycerol shown here has three different fatty acids attached to the glycerol backbone. When glycerol has different fatty acids at C-1 and C-3, C-2 is a chiral center (p. 16).

39. Membranes: Glycerophoshpolipids
FIGURE 10-9 (part 1) Glycerophospholipids. The common glycerophospholipids are diacylglycerols linked to head-group alcohols through a phosphodiester bond. Phosphatidic acid, a phosphomonoester, is the parent compound. Each derivative is named for the head-group alcohol (X), with the prefix "phosphatidyl-." In cardiolipin, two phosphatidic acids share a single glycerol (R1 and R2 are fatty acyl groups).

40. FIGURE (part 1) The similarities in shape and molecular structure of phosphatidylcholine (a glycerophospholipid) and sphingomyelin (a sphingolipid) are clear when their space-filling and structural formulas are drawn as here.

41. Sterols
FIGURE Cholesterol. The stick structure of cholesterol is visible through a transparent surface contour model of the molecule. In the chemical structure, the rings are labeled A through D to simplify reference to derivatives of the steroid nucleus; the carbon atoms are numbered in blue. The C-3 hydroxyl group (pink in both representations) is the polar head group. For storage and transport of the sterol, this hydroxyl group condenses with a fatty acid to form a sterol ester.

42. Steroids
FIGURE Steroids derived from cholesterol. Testosterone, the male sex hormone, is produced in the testes. Estradiol, one of the female sex hormones, is produced in the ovaries and placenta. Cortisol and aldosterone are hormones synthesized in the cortex of the adrenal gland; they regulate glucose metabolism and salt excretion, respectively. Prednisolone and prednisone are synthetic steroids used as antiinflammatory agents. Brassinolide is a growth regulator found in vascular plants.