Carbohydrates: Types, Structure, Composition and Uses - Biomolecules PDF

BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES ALPHA VS. BETA CARBOHYDRATES CARBOHYDRATES - The most abundant organic compounds in nature (50% of the earth’s biomass). - 3/4 of the weight of...

BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES ALPHA VS. BETA CARBOHYDRATES CARBOHYDRATES - The most abundant organic compounds in nature (50% of the earth’s biomass). - 3/4 of the weight of plants. - 1% of the weight of animals and humans (they do not store). - 65% of the foods in our diet - Found in the DNA as ribose APPROXIMATE RATIO OF CARBOHYDRATE MOLECULE Cyclic Structure — Haworth Structure Humans have α-amylase (an enzyme) and they can digest starch products such as pasta (contain α-glucose) Humans do not have β-amylase (an enzyme) and CARBOHYDRATE CLASSIFICATION they cannot digest cellulose such as wood or paper (contain β-glucose) Aldehydes and ketones react with alcohol in a 1:1 ratio to form hemiacetals or hemiketals, creating a new chiral center at the carbonyl carbon Carbohydrates * A hemiacetal/ hemiketal contains a hydroxyl group (OH) and an alkoxy group (OR) on the same carbon. Cyclic hemiacetals form readily when the hydroxyl and carbonyl groups are part of the same molecule.  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES Cyclic hemiacetals/ hemiketals contain an additional asymmetric carbon atom and can exist in two stereoisomeric forms designated as α and β. α – indicates that the hydroxyl group at the anomeric center is in a Fisher projection, on the same side as the hydroxyl attached at the farthest chiral center β – indicates that these hydroxyl groups are on opposite sides ANOMERS- isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom ANOMERIC CARBON- the hemiacetal (carbonyl) carbon atom MUTAROTATION- when the α and β anomers of D- glucose interconvert in an aqueous solution CHIRALITY All carbohydrates have 1 or more chirality centers. Glyceraldehyde, the simplest aldose, has one chirality center, and has two possible enantiomers. FISCHER PROJECTIONS -Horizontal lines represent bonds projecting forward from the stereocenter.  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES - Vertical lines represent bonds projecting to the rear. MUTAROTATION - Only the stereocenter (tetrahedral carbon) is in the Change in specific rotation that accompanies the plane. equilibration of α and β anomers in aqueous solution. PHYSICAL PROPERTIES OF MONOSACCHARIDES 1. Carbon with four different groups bonded to it. -Colorless 2. The chiral carbon furthest from the carbonyl - Sweet Tasting group (-CHO). - Crystalline solids - Polar with high melting points (because of OH groups) - Soluble in water and insoluble in nonpolar solvents (H-bond because of OH groups) CHEMICAL PROPERTIES OF MONOSACCHARIDES 1. Formation of Glycosides (Acetals) 2. Oxidation 3. Reduction FORMATION OF GLYCOSIDES (ACETALS) D - ISOMER -Exist almost exclusively in cyclic hemiacetal forms. When the hydroxyl group on the reference carbon is - They react with alcohol to give acetals. on the right in a projection formula that has a carbonyl - Acetals are stable in water and bases but they are group on top, the sugar hydrolyzed in acids. Most hexoses of living organisms are D isomers CHAIR CONFORMATION  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES OXIDATION OF MONOSACCHARIDES MONITORING GLUCOSE LEVELS REDUCTION OF MONOSACCHARIDES ~~ Sugars alcohols: sweetners in many sugar-free (diet drinks & sugarless gum). primary alcohol at C-6 of a hexose is oxidized to uronic acid by an enzyme (catalyst). Problem: diarrhea and cataract MONOSACCHARIDES SACCHARIDES – GREEK word for SUGAR With ONE sugar molecule Cannot be further reduced by HYDROLYSIS Can be directly absorbed in the bloodstream from the small intestine  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES TYPES OF MONOSACCHARIDES ACCORDING TO THE Normal blood glucose levels are 70-110 mg/dL. LOCATION OF THE CARBONYL GROUP Excess glucose is stored as the polysaccharide glycogen or as fat Insulin (a protein produced in the pancreas) regulates blood glucose levels by stimulating the uptake of glucose into tissues or the formation of glycogen. Patients with diabetes produce insufficient insulin to adequately regulate blood sugar levels, so they must monitor their diet and/or inject insulin daily CLASSIFICATION OF MONOSACCHARIDES FRUCTOSE (C6H12O6, ketohexose), SOME IMPORTANT MONOSACCHARIDES Is the sweetest of carbohydrates. GLUCOSE Is found in fruit juices and honey (fruit sugar). In the bloodstream, it is converted to its isomer, glucose. Is bonded to glucose in sucrose (a disaccharide known as table sugar). GLUCOSE (DEXTROSE) (C6H12O6 aldohexose) – Blood sugar The most abundant monosaccharide Is found in fruits, vegetables, corn syrup, and honey. Is found in disaccharides such as sucrose, lactose, and maltose. Makes up polysaccharides such as starch, cellulose, and glycogen.  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES GALACTOSE (C6H12O6, aldohexose), Has a similar structure to glucose except for the –OH on Carbon 4. Cannot find free form in nature. Exist in the cellular membranes of the brain and nervous system. Combined with glucose in lactose (a disaccharide and a sugar in milk). DISACCHARIDES Consists of two monosaccharides linked by a glycosidic bond (when one –OH group reacts with another –OH group). CARBOHYDRATE DISORDER Galactosemia GLYCOSIDIC BONDS - missing the enzyme that convert galactose to glucose a covalent bond that joins the hemiacetal group of a - GALACTOSE-1-PHOSPHATE URIDYL TRANSFERASE saccharide to the hydroxyl group of the other saccharide  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES ~~ CONDENSATION IN GLYCOSIDIC BONDING SOME IMPORTANT DISACCHARIDES MALTOSE -Is a disaccharide of two glucose molecules. Has a α -1,4-glycosidic bond (between two α-glucoses). Is obtained from the breakdown of starches. Is used in cereals and candies. Is a reducing sugar (carbon 1 can open to give a free aldehyde to oxidize). LACTOSE -Is a disaccharide of galactose and glucose. Has a β -1,4-glycosidic bond (between β-galactose and α-glucose). Is found in milk and milk products (almost not sweet). Is a reducing sugar (carbon 1 can open to give a free aldehyde to oxidize) SUCROSE -Is found in table sugar (obtained from sugar cane and sugar beets).  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES Consists of glucose and fructose. Has an α,β-1,2-glycosidic bond (between α-glucose and β-fructose). Is not a reducing sugar (carbon 1 cannot open to give a free aldehyde to oxidize). Saccharine: Sucrose is very sweet, but contains many calories. -It (sold at Sweet’n Low) was used extensively during World War I. To reduce caloric intake, many artificial sweeteners have been developed. - There were concerns in the 1970s that saccharin causes cancer. Aspartame, Saccharin, Sucralose These artificial sweeteners were discovered accidentally Sucralose: -It (sold as Splenda) has a very similar structure to sucrose. ARTIFICIAL SWEETENERS Aspartame: -It (sold as Equal) is hydrolyzed into phenylalanine, which cannot be processed by those individuals with the condition phenylketonuria. OLIGOSACCHARIDES carbohydrates that contain between 3 and 10 single sugar residues not relatively abundant in the diet when compared to other more common carbohydrates like those in the disaccharide category.  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES Maltotriose is a trisaccharide (three-part sugar) consisting of three glucose molecules linked with α-1,4 glycosidic bonds. Maltotriose is a metabolite found in or produced by Escherichia coli (strain K12, MG1655) POLYSACCHARIDES Polymers of many monosaccharides units. Starch - Amylose (20%) - Amylopectin (80%) The raffinose family of oligosaccharides comprise: Glycogen (an energy storage in animals & humans) raffinose (trisaccharide), stachyose (tetrasaccharide) and, verbascose (pentasaccharide) Cellulose (plant and wood structures). all occur in the seeds of legumes, as well as in different parts of plants  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES. SOME IMPORTANT POLYSACCHARIDES AMYLOSE -Is a polysaccharide of α-glucose in a continuous (unbranched) chain (helical or coil form). Has α-1,4-glycosidic bonds between the α-glucose units (250 to 4000 units). GLYCOGEN - It is similar to amylopectin (more highly branched-every 10-15 units). It is an energy storage molecule found in animals/humans. It is stored mainly in the liver and in muscle cells. When glucose is needed for energy, glucose units are hydrolyzed from the ends of the glycogen polymer. is highly branched, there are many ends available for AMYLOPECTIN hydrolysis -Is a polysaccharide of glucose units in branched chains. Has α-1,4-glycosidic bonds between the α-glucose units. Has α-1,6 bonds to branches of glucose units. (at about every 25 glucose units, there is a branch). Both forms of starch are water soluble  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES POLYSACCHARIDES -Cellulose makes up the insoluble fiber in our diets. - It passes through the digestive system without being RESPIRATION metabolized. - Fiber is important in adding bulk to waste to help eliminate it more easily (even though it gives us no nutrition). CELLULOSE -Is a polysaccharide of glucose units in unbranched chains with β-1,4-glycosidic bonds (2200 glucose units). Has rigid structure (H-bond) and insoluble in water. Is the major structural material of wood & plants USEFUL CARBOHYDRATES (cotton: 100%). Amino Sugars Cannot be digested by humans because of the β-1,4-glycosidic bonds (needs an enzyme: -They contain an -NH2 group in place of an -OH group. β-glycosidase). - The most abundant amino sugar in nature is D-glucosamine. - Glucosamine helps keep the cartilage in joints healthy. But natural glucosamine levels drop as people age. - As a supplement, glucosamine is most often used to try to ease the joint pain caused by arthritis.  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES - The second most abundant amino sugar in nature is Chitin. - It is a polysaccharide formed from Chondroitin: a component of cartilage and tendons. N-acetyl-D-glucosamine units joined together by 1,4-β-glycosidic bonds. - Its structure is similar to cellulose (insoluble in water) Heparin: stored in the mast cells of the liver, helps prevent blood clotting. BLOOD TYPE Type A blood contains a fourth monosaccharide: Glycosaminoglycans (GAGs) -They are a group of unbranched carbohydrates derived from alternating amino sugar and glucuronate units. Hyaluronate: extracellular fluids that lubricate joints and in the vitreous humor of the eye.  BIOMOLECULES CARBOHYDRATES: TYPES, STRUCTURE, COMPOSITION AND USES Type B contains an additional D-galactose unit. Type AB has both type A and type B carbohydrates. - The short polysaccharide chains distinguish one type of the red blood cell from another, and signal the cells about the foreign viruses, bacteria, and other agents. - The blood of one individual may contain antibodies to another type. - Those with type O blood are called universal donors, because people with any other blood type have no antibodies to type O. - Those with type AB blood are universal recipients because their blood contains no antibodies to A, B, or O.