Copyright © Houghton Mifflin Company. All rights reserved.3–13–1 Biochemistry Biochemistry is the study of chemical substances found in living systems and the chemical interactions of these substances with each other. A biochemical substance is a chemical substance found within a living organism.

Copyright © Houghton Mifflin Company. All rights reserved.3–23–2 Biochemistry Biochemistry

Copyright © Houghton Mifflin Company. All rights reserved.3–33– Intro to Carbohydrates Carbohydrates are biomolecules that decom- pose to produce carbon and water. Their empirical formulas are approximately CH 2 O. Carbohydrates are produced in plants by photosynthesis.

Copyright © Houghton Mifflin Company. All rights reserved.3–43– Intro to 14 Carbohydrates Carbohydrates are scarce in animals, but account for ~75% of dry mass in plants. Uses of carbohydrates: Oxidized to provide energy Serve as stored form of chemical energy Supply carbon for biosynthesis in cells Form structures of some cells and tissues Are markers on cell surfaces

Copyright © Houghton Mifflin Company. All rights reserved.3–53– Types of Carbohydrates Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, or substances that produce such compounds by hydrolysis.

Copyright © Houghton Mifflin Company. All rights reserved.3–63– Types of Carbohydrates Carbohydrates are classified by size. Mono- saccharides contain one polyhydroxycarbonyl unit. Larger carbohydrates contain chains of these units, linked by covalent bonds.

Copyright © Houghton Mifflin Company. All rights reserved.3–73– Types of Monosaccharides Monosaccharides are classified by 1. The type of carbonyl group: Aldose or Ketose 2.The number of carbons: Triose (3 carbons) Tetrose (4 carbons) Pentose (5 carbons) Hexose (6 carbons) Competency XIII-1

Copyright © Houghton Mifflin Company. All rights reserved.3–83– Types of Monosaccharides Monosaccharides

Copyright © Houghton Mifflin Company. All rights reserved.3–93– Handedness Shapes of molecules are incredibly important in biochemistry. Molecules that have the same formula but different shape are called isomers. There are several types of isomers: Constitutional Isomers Stereoisomers Geometric Optical

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Types of isomers: Constitutional isomers, or structural isomers, are isomers that differ in their bonding sequence or connectivity.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Types of isomers: Stereoisomers are isomers that differ only in how their atoms are oriented in space. The connectivity is the same in all the isomers. There are two types of stereoisomers. Geometric isomers, or cis-trans isomers:

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Types of isomers: Optical isomers are mol- ecules that interact with polarized light. The simplest of these are nonsuperimposable mirror images of each other. They are called enantiomers.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Molecules that can have enantiomers must have chiral centers. Chiral centers are tetrahedral carbons with four different substituents. The substituents can be individual atoms or functional groups.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Pairs of molecules with nonsuperimposabl e mirror images are called enantiomers.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Carbohydrates have many stereoiso- mers. Glyceraldehyde, the simplest carbohy- drate, has enan- tiomers. It is an aldotriose.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Each enantiomer in a pair has the same prop- erties unless it interacts with another chiral substance. Biological molecules are usually chiral.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Compounds can have more than one chiral center. The number of stereoisomers is 2 n, where n is the number of chiral centers.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness Stereoisomers of compounds with more than one chiral center that are not enantiomers (mirror images) are called diastereomers. A B C D A & B, C & D, pairs of enantiomers A is a diastereomer of C & D.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness In carbohydrates, handedness is shown in Fischer projections. The right-handed isomer is the D-(dextro) isomer; the left- handed isomer is the L-(levo) isomer.

Copyright © Houghton Mifflin Company. All rights reserved.3– Handedness In carbohydrates with many chiral centers, the carbon furthest from the carbonyl group is used for this designation. Naturally occuring car- bohydrates are all D- isomers.

Copyright © Houghton Mifflin Company. All rights reserved.3– Cyclization Monosaccharides contain carbonyl and hydroxyl groups. These react to form hemiacetals. The reactions are spon- taneous, intramolecular, and form cyclic products. Ring size: 6 atoms pyranose 5 atoms furanose

Copyright © Houghton Mifflin Company. All rights reserved.3– Cyclization Ring size: 6 atoms pyranose 5 atoms furanose

Copyright © Houghton Mifflin Company. All rights reserved.3– Cyclization Hemiacetals can form in two orientations: 36% 64%

Copyright © Houghton Mifflin Company. All rights reserved.3– RXN’s of Monosaccharides Aldoses are easily oxidized. Benedict’s test with Cu 2+ can be used to detect them. Tollens’ test, which produces metallic silver, is also useful.

Copyright © Houghton Mifflin Company. All rights reserved.3– RXN’s of Monosaccharides Positive Benedict’s test.

Copyright © Houghton Mifflin Company. All rights reserved.3– RXN’s of Monosaccharides Carbonyl groups in monosaccharides can be reduced to hydroxyl groups. The products are sugar alcohols.

Copyright © Houghton Mifflin Company. All rights reserved.3– RXN’s of Monosaccharides In the presence of alcohols, monosaccharides form cyclic acetals called glycosides.

Copyright © Houghton Mifflin Company. All rights reserved.3– Disaccharides Disaccharides contain two monosaccharide units. They are bonded together through acetal/glycoside linkages. One monosac- charide supplies the carbonyl in hemiacetal form; the other provides the alcohol.

Copyright © Houghton Mifflin Company. All rights reserved.3– Disaccharides Maltose is composed of two glucose units joined by an  (1  4) glycoside linkage.

Copyright © Houghton Mifflin Company. All rights reserved.3– Disaccharides Lactose is composed of galactose and glucose units united in a  (1  4) linkage.

Copyright © Houghton Mifflin Company. All rights reserved.3– Disaccharides Lactose is the sugar found in milk. Lactose intolerance occurs when a person does not produce the enzyme to hydrolyze the  (1  4) glycoside linkage. Infants and children have the enzyme, but many adults do not.

Copyright © Houghton Mifflin Company. All rights reserved.3– Disaccharides Sucrose contains glucose and fructose units joined in an ,  (1  2) linkage.

Copyright © Houghton Mifflin Company. All rights reserved.3– Polysaccharides The major polysaccharides are polymers of glucose. In cellulose, the glucose units are joined by  (1  4) glycoside linkages.

Copyright © Houghton Mifflin Company. All rights reserved.3– Polysaccharides Cellulose is the major structural carbohydrate in plants. Animals lack the enzyme cellulase, which catalyzes hydrolysis of the  (1  4) glyco- side linkages. They (we!) cannot metabo- lize cellulose for nutrition. Grazing animals and termites have bacteria in their guts that produce the enzyme; these animals can feed on grass and wood.

Copyright © Houghton Mifflin Company. All rights reserved.3– Polysaccharides Starches are also polymers of glucose. They are used for energy storage in plants. There are two forms, amylose and amylopectin. Amylose is a straight-chain polymer in which glucose units are linked by  (1  4) glyco- side linkage. Amylopectin is a branched-chain polymer. The branches are formed by  (1  6) link- ages.

Copyright © Houghton Mifflin Company. All rights reserved.3– Polysaccharides Comparison of amylose and amylopectin structures.

Copyright © Houghton Mifflin Company. All rights reserved.3– Polysaccharides Amylopectin, showing glycoside linkages.

Copyright © Houghton Mifflin Company. All rights reserved.3– Polysaccharides Glycogen, sometimes called animal starch, is structurally similar to amylopectin. Glycogen is formed when excess glucose is present in the blood; the process is called glycogenesis. Glycogen is stored in the liver and muscle tissue. When blood glucose is low, glycogen is hydrolyzed to release glucose. The process is called glycogenolysis.