Carbohydrates CHEM233 Final Notes PDF

Carbohydrates Engr. Renee Niña T. Colanag Carbohydrates Carbohydrates are the most abundant organic compounds in plants. They account for approximately three-fourths of the dry weight of plants. Carbohydrates Carbohydrates are the most abundant biomolecule in...

Carbohydrates Engr. Renee Niña T. Colanag Carbohydrates Carbohydrates are the most abundant organic compounds in plants. They account for approximately three-fourths of the dry weight of plants. Carbohydrates Carbohydrates are the most abundant biomolecule in nature. They are chemically simpler than nucleic acids and proteins, containing just three elements: carbon, hydrogen and oxygen. Main Functions 1.Metabolic precursors of virtually all other biomolecules since they are the main products of the producers 2.The breaking down of carbohydrates provides energy that sustain animal life. 3.Carbohydrates covalently bonded with with other molecules known as glycoconjugates are important structural components of cell walls and extracellular structures. 4.Involved recognition between cell types or the recognition of cellular structures by other molecules. Recognition events are important in normal cell growth, fertilization and transformation of cells. Structural Definition carbohydrates are known as polyhydroxy aldehydes and ketones Classification 1. Monosaccharides 2. Disaccharides 3. Oligosaccharides 4. Polysaccharides Monosaccharid es Monosaccharides are the smallest unit of sugars which cannot be further hydrolyzed*. They mostly contain 3-6 C atoms, and has one stereogenic carbon, except for dihydroxyacetone. Classification 2 ways to classify monosaccharides: 1. According to the number of carbon atoms 2. According to the type of carbonyl group Sample Problem 1 1. What is the classification of the monosaccharide according to: a. number of carbons b. type of carbonyl 2. What is the combined classification of the monosaccharide Sample Problem 2 1. What is the classification of the monosaccharide according to: a. number of carbons b. type of carbonyl 2. What is the combined classification of the monosaccharide NAMING SUGARS NAMING SUGARS Aldoses Ketoses Stereochemistry Stereochemistry is the study of different spatial arrangements of atoms in molecules.  Isomers Structural Isomers Stereoisomers: enantiomers, diastereomers, cis-trans isomers Monosaccharide Isomers Isomers are molecules having the same molecular formula but differ in their arrangement, connectivity and orientation in space resulting to be different molecules Monosaccharide Isomers Constitutional Isomers - same formula but different functional groups Monosaccharide Isomers Stereoisomers have the same molecular formula and functional group but different orientation of atoms around the molecule The difference in orientation of atoms in our stereoisomers are usually occuring in our stereogenic carbons. It is a saturated carbon with 4 differebt carbons around it. Types of Stereoisomers Enantiomers - non- superimposable mirror images of each other. D and L notation D and L notation and is determined based on the chiral carbon farthest from the C=O carbonyl group (penultimate carbon or 2nd to the last) Monosaccharide Isomers Diastereomers - stereoisomers that are not mirror images of each other. Monosaccharide Isomers Epimers - a special class of diastereomers that differ in the position of only one -OH group Cyclic Structure of Monosaccharides Alcohols react with carbonyl of aldehydes and ketones to form hemiacetals and hemiketals. “hemi-“, meaning half, because the - OH formed reacts with another Monosaccharides with both alcohol forming full acetals and ketals. alcohol and carbonyl, their hydroxyl and either aldehyde or ketones can react intramolecularly to form cyclic hemiacetals and hemiketals. Cyclic Structure of Monosaccharides Glucose undergoing an intramolecular reaction. The aldehyde group reacts with it‘s penultimate hydroxyl group resulting in a 6- membered, oxygen- containing ring which is similar to pyran. Designated as a pyranose Cyclic Structure of Monosaccharides Fructose undergoing an intremolecular reaction where the ketone group of fructose reacts with the penultimate hydroxyl group yielding a 5- membered, oxygen containing ring that is similar to furan Designated as a furanose Cyclic Structure of Monosaccharides In equilibrium, the cyclic pyranose and furanose forms are the preferred sstructures of monosaccharides in aqeous solution. Linear aldehyde or ketone structure is only a minor component in the mixture. Cyclic Structure of Monosaccharides  An α anomer has the –OH of the anomeric carbon in opposite direction as the terminal –CH2OH.  A β anomer has the –OH of the anomeric carbon in similar direction as the terminal –CH2OH. Monosaccharide Derivatives Monosaccharides undergoes the same reactions as common carbonyls and alcohols. These reactions result to the modification of the functional groups forming sugar derivatives. ⚬ 1. Sugar Acids ⚬ 2. Sugar Alcohols ⚬ 3. Amino Sugars ⚬ 4. Sugar Phosphates Sugar Acids Sugar Acids Aldoses have an aldehyde group and a primary group. With 2 possible sites of oxidation they yield 3 different sugar acids. ⚬ 1. Aldonic Acid (from -ose to -onic acid) ￭ weak oxidizing agents ⚬ 2. Aldaric Acid (from -ose to -aric acid) ￭ strong oxidizing agents ⚬ 3. Alduronic Acid (Uronic Acid) (-ose to -uronic aicd) ￭ enzymatic oxidation ￭ α–D–glucuronic acid is used by the body to detoxify foreign phenols and alcohols; in the liver, these compounds are converted to glycosides of glucuronic acid and excreted in the urine Aldonic Acid When open chain aldoses react with weak oxidizing agents, their aldehydes are converted into carboxylic acids. This form aldonic acids. The weak oxidizing agents are often a metal ion solution in basic condition. The aldonic acids is named by replacing –ose with –onic acid. Aldaric Acid When aldoses are reacted with strong oxidizing agents (e.g. hot concentrated nitric acid (HNO3)), their aldehydes and primary alcohols are both converted to carboxylic acids. The aldaric acid that is produced is named by replacing the suffix –ose in the original name of aldose with the suffix -aric acid. Alduronic Acid Monosaccharides can undergo enzymatic oxidation at their primary alcohols converting them to carboxylic acids. This produces alduronic acids or simply uronic acids. The alduronic acid that is produced is named by replacing the suffix – ose in the original name of aldose with the suffix - uronic acid Sugar Alcohols Reduction of an aldehyde of an aldose or a ketone of a ketose into a primary and a secondary alcohol, respectively. ( from -ose to itol) Sugar Alcohols Common alditols and their functions: 1. Xylitol – component of sugar free gum 2. Glucitol or sorbitol is found in the plant world in many berries and in cherries, plums, pears, apples, seaweed, and algae. It is also used as a sweetening agent. Accumulation of sorbitol in the eye is a major factor in the formation of cataracts. 3. Mannitol is now used in the treatment of malignant brain tumors. Amino Sugars ⚬ If one of the hydroxyl groups of a monosaccharide is replaced with an amino group (NH2), an amino sugar is produced. (from -e to -amine) ⚬ There are 3 naturally occurring amino sugars. In all three, the amino group replaces the hydroxyl group at carbon 2. Amino Sugars ⚬ Amino sugars and their N-acetyl derivatives are important building blocks of chitin and hyaluronic acid. N-acetyl derivatives of glucosamine and galactosamine acts as biochemical markers of red blood cells which distinguishes various blood types Amino Sugars ⚬ N-acetyl derivatives of glucosamine and galactosamine acts as biochemical markers of red blood cells which distinguishes various blood types Sugar Phosphates The –OH group (usually at C1 and C6) of a monosaccharide can react with phosphoryl group to form phosphate esters. In biological systems, phosphoryl group is usually from ATP. Sugar Phosphates Sugar phosphates are produced as intermediates in metabolism. One effect of sugar phosphorylation within cells is to trap the sugar inside the cell; most cells do not have plasma membrane trans-porters for phosphorylated sugars. Glycosides The hydroxyl group of a hemiacetal or hemiketal can react with alcohol to form an acetal or ketal, respectively. This reaction is considered a dehydration synthesis reaction since a new bond is formed with concomitant removal of H2O. Glycosides pyranose or furanose forms of monosaccharides can react with alcohol in the same manner to form glycosides with retention of the α and β configuration at the anomeric carbon  Disaccharides Disaccharides are carbohydrates comprising 2 monosaccharide units which are linked together via glycosidic bond. Each monosaccharide unit is known as a residue. Dissaccharides are crystalline in appearance, imparts sweet taste, and can undergo fermentation and hydrolysis.  Formation of Disaccharides Disaccharides are formed where the –OH of the anomeric carbon of a first monosaccharide reacts with any –OH of a second disaccharide.  General Structure Disaccharides are formed where the –OH of the anomeric carbon of a first monosaccharide reacts with any –OH of a second disaccharide. General Structure Acetal carbon – nonreducing end Free hemiacetal carbon – reducing end. the free anomeric carbon has the potential to be converted to aldehyde configuration and thus can participate in oxidation-reduction reaction of reducing sugars General Structure Acetal carbon – nonreducing end Free hemiacetal carbon – reducing end. the free anomeric carbon has the potential to be converted to aldehyde configuration and thus can participate in oxidation-reduction reaction of reducing sugars Glycosidic Bonds The glycosidic bond also plays important role in the chemistry and physiological functions of disaccharides, and even for polysaccharides. Some disaccharides have similar monosaccharide units, but only differ in the configuration of their glycosidic bonds. Glycosidic Bonds: configuration The glycosidic bond also plays important role in the chemistry and physiological functions of disaccharides, and even for polysaccharides. Some disaccharides have similar monosaccharide units, but only differ in the configuration of their glycosidic bonds. Glycosidic Bonds In maltose, the α in the designation above indicates the type of anomer of the monsaccharide whose anomeric carbon is involved in the glycosidic bond. The (14) indicates that the glycosidic bond is between carbon 1 (C1) of the first monosaccharide and carbon 4 (C4) of the second monosaccharide. Glycosidic Bonds cellobiose sucrose Sucrose Also known as table sugar, it is the most abundant disaccharide in the biological world. - Sugar cane and sugar beets - Sucrose is a non-reducing sugar  Maltose A component of malt. It is produced from starch. Malt is a substance produced by allowing barley to soften in water and germinate. It is important to the brewing of beer. It is a reducing disaccharide.  Lactose Lactose is the principal sugar present in milk. It accounts for 5 to 8% of human milk and 4 to 6% of cow’s milk. This disaccharide consists of D- galactopyranose bonded by a b-1,4- glycosidic bond to carbon 4 of D-glucopyranose. Lactose is a reducing sugar  Cellobiose Produced by the hydrolysis of cellulose. This monosaccharide cannot be hydrolyzed in the human body, as humans have no β-glucosidase enzymes capable of hydrolyzing β glycosidic bonds between glucose units.  Hydrolysis of Disaccharides Hydrolysis is the breakdown of a large molecule into simpler units in the action of water. It is a reaction that is considered to be reverse of dehydration, because in this case water acts as a reactant. Disaccharides can hydrolyzed in the presence of acid or enzymes to produce corresponding monosaccharides.  Disaccharidases 1. Lactase – a β-galactosidase; enzyme capable of cleaving lactose due to its ability to hydrolyze β glycosidic bonds in galactose. 2. Maltase – an α-glucosidase; cleaves the α(14) glycosidic bond in maltose. 3. Sucrase-isomaltase complex – an enzyme with 2 functional subunits, the first one that cleaves the α,β(12) glycosidic bond in sucrose; and the second one that cleaves α (16) glycosidic bond in isomaltose.  Lactose Intolerance - mainly a digestive disorder characterized by the inability to digest lactose. This is caused by the deficiency of lactase. Symptoms: bloating, diarrhea and dehydration. When there is not enough lactase in the body, lactose will not be hydrolyzed and will only proceed to the large intestine. ONLY MONOSACCHARIDES CAN BE ABSORBED BY SMALL INTESTINAL CELLS.  Lactose Intolerance - mainly a digestive disorder characterized by the inability to digest lactose. This is caused by the deficiency of lactase. Symptoms: bloating, diarrhea and dehydration. When there is not enough lactase in the body, lactose will not be hydrolyzed and will only proceed to the large intestine. ONLY MONOSACCHARIDES CAN BE ABSORBED BY SMALL INTESTINAL CELLS.  Polysaccharides By far the majority of carbohydrate material in nature occurs in the form of polysaccharides. Polysaccharides, also called glycans, consist of polymers of monosaccharides and/or their derivatives. Homopolysaccharide or homoglycan – 1 kind of monosaccharide Heteropolysaccharide – more than 1 kind of monosaccharide  Common Properties 1. Amorphous powder in appearance 2. Does not impart sweet taste 3. Can be hydrolyzed but do not undergo fermentation 4. All polysaccharides are non-reducing although they usually have a free anomeric carbon at the end. However, this single free anomeric carbon is not enough compared to the molecular size of a polysaccharide. 5. They have limited solubility in water due to their size, however the–OH in their structures can individually be hydrated with water molecule resulting in a thick colloidal suspension of a polysaccharide in water.  Factors in Identifying Polysaccharides differ in:  nature of their component monosaccharides,  type of glycosidic bond,  length of their chains, and  amount of chain branching. Types of Polysaccharides Polysaccharides function as storage material, structural components, or protective substances. Activity By pair. ½ CW. List and describe 2 examples each of polysaccharides according to their function. Storage Polysaccharides These polysaccharides function as storage forms of monosaccharides and are used as energy source in cells. Storage Polysaccharides Starch –most common storage polysaccharide. -Homopolysaccharide of α-D-glucose units and only α linkages that folds in a helical form. Storage Polysaccharides Starch: Amylose: minor component of starch which only 10-20%. It can solubilize when treated in boiling water. -300-500 glucose units with glycosidic bonds Storage Polysaccharides Starch: Amylopectin: major component and accounts for 80-90% of starch. It cannot be dissolved in boiling water, but instead forms paste-like gel. -highly branched with glycosidic bonds between linear units of glucose and branching with glycosidic bonds. Storage Polysaccharides Humans have enzymes that makes us capable of hydrolyzing α. α-salivary-amylase – the major enzyme secreted by salivary glands. Raw starch is not very susceptible to salivary endoamylase. When heated, the starch granules swell causing the polymer to become accessible to enzymes thus cooked starch is more digestible. Storage Polysaccharides Glycogen: animal starch. Major form of storage polysaccharide in animals. Mostly found in liver cells and in muscle cells. Similar to amylopectin in structure but more branched than amylopectin. Storage Polysaccharides When glucose in blood is present in excess amount, liver and muscle cells convert the excess glucose to glycogen. When glucose level drops, stored glycogen hydrolyzes back to glucose. Structural Polysaccharides These polysaccharides serve as structural component in plant cell walls and animal exoskeletons. The most important structural polysaccharides are cellulose and chitin. Structural Polysaccharides Cellulose: most abundant naturally occurring polymer in the world. It is found in almost all plant cell walls. It is the principal component providing physical structure and strength. Structurally similar to amylose being linear homopolysaccharide of D-glucose units however being linked with glycosidic bonds. Structural Polysaccharides Cellulose: most abundant naturally occurring polymer in the world. It is found in almost all plant cell walls. It is the principal component providing physical structure and strength. Structurally similar to amylose being linear homopolysaccharide of D-glucose units however being linked with glycosidic bonds. Common Disaccharides 1.Maltose 2.Cellobiose 3.Lactose 4.Sucrose