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Biochemistry

Biochemistry. Carbohydrates. Carbohydrates. Literally, it means “carbon water”, and all carbohydrates have the general formula C n (H 2 O) m —where n and m can be the same or nearly so

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Biochemistry

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  1. Biochemistry Carbohydrates

  2. Carbohydrates Literally, it means “carbon water”, and all carbohydrates have the general formula Cn(H2O)m—where n and m can be the same or nearly so Carbohydrates are made by plants, where 75% of the solid plant is carbohydrate. They are involved in both the structure and energy storage for the plant Though not a major part of animal tissue, they are very important in the structure of the exoskeletons of crustaceans and other arthropods

  3. Classes of Carbohydrates Monosaccharides—simple sugars, cannot be hydrolyzed Disaccharides—composed of two monosaccharides Polysaccharides—made of many, up to 3000, monosaccharides Monosaccharides are further classed by how many carbons: 3=triose, 4=tetrose, 5=pentose, 6=hexose They are also classed by the type of carbonyl group in the molecule: aldehyde=aldose ketone=ketose Examples: ribose is an aldopentose, fructose is a ketohexose

  4. Monosaccharides Properties: colorless crystalline solids highly water soluble with a sweet taste Important monosaccharides: glucose, fructose, galactose, ribose, deoxyribose Glucose is the most common hexose, an aldose found in nature, primarily in fruit juices, and is the immediate source of energy within cells Glucose is a main component of many di- and polysaccharides

  5. Glucose Structure: straight chain, not common in nature Ring forms—two variations, linkage is an acetal between 1st and 5th carbons Short form: The #1 carbon makes the difference in the forms

  6. Optical Isomerism Biochemical exhibit an additional type of isomerism, the twisting of light due to differences in the molecule A carbon with four different atoms attached to it will have chirality, that is it cannot be superimposed upon its mirror image, just like a left hand glove cannot go onto your right hand

  7. Optical Isomerism Chirally different molecules affect polarized light by bending it in opposite directions, either to the right (dextrorotatory) or left (levorotatory) Living organisms will only use one or the other optical isomer due to enzyme matching…example Splenda

  8. Other Monosaccharides Fructose—a ketose, very sweet, found in honey straight form: ring form, a hemiketal Galactose—aldohexose linked with glucose in lactose, very similar to glucose except for the #4 carbon

  9. Pentoses The most important 5 carbon sugars are ribose and deoxyribose, found in the nucleic acids RNA and DNA respectively ribose: deoxyribose: note difference

  10. Reducing Sugars If a sugar contains a free or potentially free aldehyde or ketone group, it will react with Cu+2 (Benedict’s) or Ag+ (Tollen’s) reagents. Positive results are brick red or black, depending on the reagent These tests can be used to detect sugar in urine

  11. Homework 15a p. 389 CYU all p. 398ff 2, 3, 7, 11, 13

  12. Disaccharides Maltose: malt sugar, a combination of two a-glucose molecules by condensation Lactose—milk sugar, combination of glucose and galactose by a b-1,4 linkage

  13. Disaccharides Sucrose—table or cane sugar, a combination of glucose and fructose by an a-1,4 linkage. Since both the aldehyde and ketone of the two sugars are involved in the linkage, sucrose is not a reducing sugar

  14. Polysaccharides Starch—very long chain/branched chain structure with molar mass between 150,000 and 6 million. It is connected like maltose, a-1,4 . Starch is the storage form of glucose used by plants, and is one of the primary sources of glucose in our diet. It can be converted to dextrins (like the browning of toast) by heat

  15. Tests for Carbohydrates Starch can be detected by the iodine test, since it will make a blu-black complex with starch. Dextrins will cause a reddish color, but monosaccharides will give no reaction The Molisch test will detect any kind of carbohydrate. The positive is a red-violet ring The Seliwanoff test will differentiate between aldoses and ketoses. Ketoses give a red color and aldoses give a pink color.

  16. Polysaccharides Glycogen—the storage form of glucose in animals and man, similar to starch, but heavily branched in a 1,6-linkage Your body stores glycogen in the liver for release of glucose from it when needed

  17. Polysaccharides Cellulose—similar to starch in that it is made entirely of glucose, but instead of the a-form, the b-form is 1,4 linked in what looks like an up-down sequence: This makes a long fibrous molecule; very strong and rigid; this makes up the strength of plants. Cellulose is the wrong shape to be digested by our digestive system, so it makes up fiber. Some microorganisms in ruminant animals can digest it so that those animals can get glucose by that process.

  18. Photosynthesis The energy stored in carbohydrates comes from the sun by way of photosynthesis. It is a very complex series of reactions which builds the monosaccharide glucose from water and carbon dioxide: This reaction is part of the carbon cycle by which carbon is reused throughout the environment

  19. Homework 15b p. 397 CYU all p. 400ff 25, 26, 27, 29, 30, 33, 34

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