Carbohydrates.pdf

LESSON PROPER INTRODUCTION: The name carbohydrate originally meant a compound with the empirical formula CH2O, literally, a hydrate of carbon. This definiHon has been broadened to include aldehydes and ketones having two or more hydroxyl groups. Among the compounds that fall into the class of carboh...

LESSON PROPER INTRODUCTION: The name carbohydrate originally meant a compound with the empirical formula CH2O, literally, a hydrate of carbon. This definiHon has been broadened to include aldehydes and ketones having two or more hydroxyl groups. Among the compounds that fall into the class of carbohydrates are the starches, cellulose, glycogen and the sugars. The carbohydrates are important source of energy for all organisms and form the supporHng Hssue of plants and some animals. There are three important classes of carbohydrates: the monosaccharides, disaccharides and the polysaccharides. (Holtzclaw and Robinson, 1988) CARBOHYDRATES - Commonly known as sugars - They are defined as polyhydroxy aldehydes or polyhydroxy ketones or substances that yield these compounds when hydrolyzed IMPORTANCE AND FUNCTIONS OF CARBOHYDRATES 1. Energy Yielding Nutrients – they serve as primary source of metabolic fuel needed by a living body and as means to store and reserve energy in the form of glycogen 2. Serve as structural components of the living cells - as carbohydrates combine with proteins, they from glycoproteins and proteoglycans that are very important components of the cell membrane 3. Serve as structural framework – for DNA and RNA as part of nucleoHdes 4. Mediate InteracHon between cells – blood types are determined by specific membrane bound CHO 5. Building materials – cellulose is found in wood, co\on, paper CLASSIFICATION OF CARBOHYDRATES - The simplest structural unit of carbohydrate is known as saccharide - In LaHn, Saccharine means sugar A. According to number of saccharide units - Monosaccharides o The simplest carbohydrate – has only one saccharide unit o Cannot be broken into smaller CHO molecules by hydrolysis - Disaccharides o Contains two monosaccharide units o It can be hydrolyzed to give two monosaccharide units - Oligosaccharide o Polymers made up of two to 10 (2-10) monosaccharide units - Polysaccharides o Giant polymers made of many monosaccharide units o The most complex CHO because they contain more than 10 saccharide units B. According to number of carbon atoms Page 146 of 334 BCHMLS 1 - Trioses – with three carbon atoms - Tetroses – with four carbon atoms - Pentoses – with five carbon atoms - Hexoses – with six carbon atoms - Heptoses – with seven carbon atoms TheoreHcally, a monosaccharide can have any number of carbons greater than three, but only monosaccharide of three to seven carbons are commonly found in the biosphere C. According to its funcHonal group o The funcHonal group of carbohydrates is the carbonyl group (-C=O) - Aldose - polyhydroxy aldehyde and the carbonyl group is found at one of the terminal sides of the hydrocarbon chain - Ketose - polyhydroxy ketone and the carbonyl group is found in between 2 hydrocarbon groups h\ps://www.mikeblaber.org/oldwine/BCH4053/Lecture12/Lecture12.htm h\p://www.hammiverse.com/lectures/5/1.html D. As a furanose or pyranose - Depends on whether the cyclic structure of the carbohydrate is related to that of the five or six-membered ring compound furan or pyran respecHvely Page 147 of 334 BCHMLS 1 h\ps://www.quora.com/What-are-the-differences-between-furanose-and-pyranose E. As Alpha or beta configuraHon - Based on the –H and –OH groups about a specific chiral carbon in the cyclic form of the monosaccharide Epimers: - two sugars which differ only in the configuraHon around a single C atom h\ps://socraHc.org/quesHons/can-anyone-explain-to-me-how-to-idenHfy-epimers-and- anomers-in-carbohydrates-su Asymmetric Carbon - refers to the C atom in the structure of a sugar to which 4 different radicals are a\ached. Page 148 of 334 BCHMLS 1 h\ps://www.quora.com/What-is-the-difference-between-symmetric-asymmetric-carbon-atom- in-carbohydrates the asymmetric carbon gives rise to the following: OpHcal acHvity/ MutarotaHon - the ability of a sugar soluHon to bend or deflect plane of polarized light. - (d or + ) DEXTROROTATORY (to the right) - ( l or - ) LEVOROTATORY (to the lel) EnanHomers (mirror-image isomers) - Stereoisomerism/ enanHomerism o Depends on the spaHal orientaHon of the –H and –OH group a\ached to the carbon atom adjacent to the terminal primary alcohol group o the ability to form two sugars which are mirror images to each other (D- isomer or L-isomer). o The configuraHon is based on the locaHon of the –OH linked to the C atom which is the next to the terminal. h\ps://slideplayer.com/slide/12282699/ D-isomer: -OH is on the RIGHT of the C atom adjacent to the terminal primary alcohol group L-isomer: -OH is on the LEFT of the C atom adjacent to the terminal primary alcohol group. MONOSACCHARIDES - Simplest carbohydrates which cannot be broken down into smaller carbohydrate molecules Page 149 of 334 BCHMLS 1 1. Trioses (C3H6O3) – glyceraldehyde, dihydroxyacetone 2. Tetroses (C4H8O4) – erthyrose, erythrulose 3. Pentoses (C5H10O5) – xylose, ribose, deoxyribose, arabinose, rhamnose 4. Hexoses (C6H12O6) – glucose, galactose, mannose, fructose 5. Heptoses (C7H14O7) – mannoheptose, mannoheptulose Chemical structure of monosaccharides 1. The carbon skeleton is unbranched 2. All the Carbon atom except one has a hydroxyl (-OH) group 3. One has a carbonyl oxygen which may be in terminal posiHon to give rise to an aldehyde (aldose), or may be located on the second carbon atom giving rise to an ketone (Ketose) 4. The terms aldose for hydroxyaldehydes and ketose for hydroxyketones specify the funcHonal group of a monosaccharide 5. The general formula of carbohydrates: Cn(H2O)n Where n = number of carbon atoms 6. It includes both the aldehyde and the ketone groups (funcHonal groups) 7. Hydroxyl groups are a\ached to each C atoms, except that of the carbonyl group IMPORTANT MONOSACCHARIDES 1. Diose – a monosaccharide with 2 carbon sugars - They are the simplest carbohydrates o Example: Glycoaldehyde 2. Triose – a monosaccharide with three carbon atoms - Glyceraldehyde o Produced from the breakdown of larger monosaccharides o D-glyceraldehyde with D-glyceraldehyde – 3 – phosphate is an intermediate in the metabolic pathway of glycolysis (conversion of glucose to lacHc acid) 3. Tetroses – carbohydrates containing 4 carbon atoms - Examples o Erythrose – aldehyde tetrose/aldotetrose o Erythrulose – ketone tetrose/ketotetrose o Threose – aldehyde tetrose/aldotetrose 4. Pentose – monosaccharides with 5 carbon atoms, the most widely distributed sugars in the living systems - Ribose o Component of ribonucleic acid (RNA), RNA sugar o RNA – is a polymeric compound that plays a major role in the synthesis of protein molecules - Deoxyribose o DNA sugar o DNA – is a compound which transmits geneHc informaHon from parent to offspring by direcHng the synthesis of protein molecules - Xylose o Found in nuts o Also known as sugar alcohol o It is a sugar that is not normally metabolized o It is used to detect CHO malabsorpHon Xylose excreHon test Page 150 of 334 BCHMLS 1 - Arabinose Aler a known amount of D-xylose has been given to a paHent, its appearance in the urine is observed In normal individuals, 65% of the xylose should be absorbed intact and excreted in the urine in 5 hours A decreased amount of D-xylose in the urine indicates malabsorpHon due to intesHnal disease o Found in nuts o Known as gum sugar 5. Hexoses – monosaccharide with 6 carbon atoms o The aldohexoses, ketohexoses and aldopentoses will receive special a\enHon since they include the most important monosaccharides in living systems - Glucose (grape sugar/blood sugar/plasma sugar/dextrose) o Most common source of cellular ATP and from which most complex carbohydrates are made from o Natural sugar mostly in the D form Blood concn: 80 – 100 mg/dL Glucose - exists in D-glucose: aka Dextrose because it is dextrorotatory; - does NOT require further digesHon and may be given IV to paHents who cannot take in food by mouth - D-Galactose o brain sugar – D-glucose is found in the brain and nervous Hssue in the form of glycolipids o An aldohexose; Less than half as sweet as glucose o Not a natural sugar o Has the fastest rate of absorpHon in the intesHnes - D-Fructose (levulose/fruit sugar) o Sweetest sugar o A natural ketohexose; occurs in honey o Serves as a source of energy for the sperm cells o Liver can convert fructose to glucose Fructose: Present in honey in equal amount with glucose. It is someHmes used as dietary sugar because less is needed with the same sweetness - Levulose is another name for it because it is levorotatory - Mannose o D-Mannose is the 2-epimer of glucose exists primarily as sweet-tasHng α- (67%) or as a bi\er-tasHng β- (33%) anomer of the pyranose o Naturally-occuring aldohexose Page 151 of 334 BCHMLS 1 o Not found free in nature but is widely distributed in the form of polysaccharide. o L-Mannose is not normally used in biological systems DISACCHARIDES - Composed of two saccharide groups - Formed when two monosaccharide molecules combine by splirng out a molecule of water - The glycosidic linkage that joins the two sugars always involves the hemiacetal –OH group of one sugar and one of the OH groups of the other monosaccharide h\ps://ib.bioninja.com.au/standard-level/topic-2-molecular-biology/23-carbohydrates-and- lipids/sugar-subunits.html Important Disaccharides 1. Maltose - Malt sugar - Broken down into 2 molecules of glucose - Linkage: alpha - 1,4 - Found in combined form as starch and is one of the intermediate products in the digesHon of starch - Derived from “malHng” (soaking, germinaHng and drying of grains such as barley) - The malt produced includes malt starch and enzymes that are able to convert malt starch into maltose, which is then fermented to produce alcohol h\ps://chem.libretexts.org/Courses/Sacramento_City_College/SCC%3A_Chem_309_- _General_Organic_and_Biochemistry_(Benne\)/Text/14%3A_Carbohydrates/14.6%3A_Disacch arides 2. Cellobiose - Composed of 2 glucose molecules - Linkage: beta – 1,4 - Produced from the breakdown of the polysaccharide cellulose Page 152 of 334 BCHMLS 1 o Mammalian digesHve tracts do not secrete enzymes that can break the beta – 1,4 linkages between 2 glucose molecules h\ps://commons.wikimedia.org/wiki/File:FormaHon_du_cellobiose.PNG 3. Lactose - Also known as milk sugar - Made by combining B-D-Galactose and D-glucose - Linkage: Beta-1,4 - In the body, it is broken down by the acHon of the enzyme known as LACTASE - Deficiency of the enzyme leads to inability to absorb lactose and the condiHon called LACTASE DEFFICIENCY SYNDROME or LACTOSE INTOLERANCE - This condiHon is controlled by eliminaHng all dietary sources of lactose (e.g. dairy products, some medicaHons) h\ps://commons.wikimedia.org/wiki/File:FormaHon_du_lactose.PNG 4. Sucrose - Also known as table sugar - Made by combining alpha-D-glucose and beta-D-fructose - Linkage: alpha,beta - linkage - Considered as a non-reducing sugar, a sugar which does not react with Tollen’s or Benedict’s reagent - Main sources: sugar and sugar beets - When sucrose undergoes hydrolysis, it produces an equimolar mixture of glucose and fructose called INVERT SUGAR through the acHon of the enzyme SUCRASE or INVERTASE h\ps://bio.libretexts.org/Courses/Lumen_Learning/Book%3A_Biology_for_Non- Majors_I_(Lumen)/03%3A_Important_Biological_Macromolecules/3.03%3A_Carbohydrates Page 153 of 334 BCHMLS 1 POLYSACCHARIDES - General formula: (C6H10O5)x - Made up of several saccharide groups - they do not exhibit reducing properHes - Made up of several hexose molecules minus the corresponding molecules of water ProperHes of polysaccharides - White, tasteless, amorphous compunds - X-ray analysis: crystalline - No reducing property; do not form osazone crystals - High MW; mostly are insoluble - Non-fermentable by yeast - Upon hydrolysis, yield simple sugars and sugar derivaHves - Polysaccharides with large MW are anHgenic Homopolysaccharides - These are polysaccharides which on hydrolysis yield only one kind of monosaccharide 1. Starch – found abundantly in the plant kingdom parHcularly in fruits, cereals, seeds, bulbs and tubers - Most important consHtuent of the human diet - Occurs in the form of granules h\ps://www.slideshare.net/thelawofscience/carbohydrates-intro-11699082 2. Inulin - Found in the bulb of onions and garlic - White, odorless, tasteless powder soluble in hot water - Upon hydrolysis (by the acHon of either acid or the enzyme INULASE) yields fructose - Clinical significance: study of renal funcHon; inulin is easily excreted through the kidneys when injected intravenously 3. Glycogen - Also called animal starch - Found in the liver as storage material and in the muscles as source of energy - Occurs in yeast, algae and fungi; abundant oysters - Structure is similar to that of amylopecHn except that branching (via alpha-1,6 linkages) occurs about 8-12 glucose units (24 – 30 glucose units for amylopecHn) Glycogen amylase maltose Glycogen acid glucose Page 154 of 334 BCHMLS 1 - Monosaccharides like glucose are synthesized and stored in the muscles and liver as glycogen - When the body needs them for heat and energy purposes, they are broken down to D- glucose to supply the physiological requirement 4. Dextrin - Intermediary products of starch hydrolysis - Amorphous, white powder Dextrin amylase maltose Dextrin acid glucose - Uses: o Used as mucilage o Used in infant feeding; prevents the formaHon of large, heavy curds or milk in the baby’s stomach, thus facilitaHng digesHon o Found in some breakfast foods and malt preparaHon 5. Cellulose - Most abundant organic compound - Forms the supporHng structure of plants - Purest source: co\on - NegaHve to the iodine test - Structure: the monosaccharide units of cellulose are beta-glucose molecules connected by beta-1,4 linkages into cellobiose units o Humans cannot digest cellulose due to the absence of the enzyme capable of cleaving the beta-1,4 linkage h\ps://www.slideshare.net/thelawofscience/carbohydrates-intro-11699082 - Uses of Cellulose o Rayon – fiber made from cellulose o Cellophane – transparent cellulose sheeHng o Cellulose + HNO3 + H2SO4 = nitrocellulose (cellulose nitrate) With 12.5 – 13.4% N = gunco\on With 11 – 12% N = celluloid (used in plasHcs and photographic films) o Cellulose + aceHc acid (or aceHc anhydride) = cellulose acetate Used as a subsHtute for celluloid Fabric, upholstery and cigare\e filters o Cellulose plays an important role in human physiology by furnishing bulk or roughage which sHmulates peristalsis, thus promoHng the evacuaHon of the bowel 6. Hemicellulose o Hydrolyzed upon boiling with mineral acids o Products: pentoses and hexoses Page 155 of 334 BCHMLS 1 a. Pentosans (C5H8O4)x: widely distributed in the plant kingdom E.g gum Arabic Liberates pentose upon hydrolysis b. Hexosans (C6H10O5)x: represented by galactans (widely distributed in plants) and give rise to galactose upon hydrolysis E.g. agar-agar has very li\le food value but has been found to be very efficient in relieving chronic consHpaHon; also used in making culture media c. Hexo-pentosans: e.g. pecHn – colloidal CHO responsible for the jellying properHes of fruits Heteropolysaccharides - Yield mixtures of monosaccharides and derived products - Nitrogen-containing mucopolysaccharides o Neutral mucopolysaccharide Made up of N-acetyl-hexosamine and hexose E.g. those occurring in bacteria and the so-called “mucoids” including important immunological specific blood group substances o Acid mucopolysaccharide Contains acetylhexosamine, hexuronic acid, sulfate or phosphate examples of mucopolysaccharide: Those containing sulfate o ChondroiHn sulfate of the carHlage Hssue - contains N- acetylgalactosamine, glucuronic acid and sulfate o ChondroiHn sulfate of the skin – has 1-iduronic acid instead of glucuronic acid o Heparin – glucosamine N-sulfate, glucuronic acid and sulfate o Hyaluronic acid Main consHtuent of the ground substance of connecHve Hssues Found in synovial fluid, pleural fluid, vitreous humor and Wharton’s jelly Made of d-glucuronic acid, d-glucosamine and aceHc acid FuncHon: Lubricant CemenHng substance which allows passage of metabolites but not of the infecHve organisms It is fragmented by hyaluronidase (spreading factor), an enzyme found in bacteria, sperm and in the poisonous secreHons of repHles and other animals o Heparin Generated by certain types of cells lining arterial blood vessels and by the lung Hssues Powerful inhibitor of blood clorng thus prevenHng intravascular coagulaHon In pracHce, it is used to prevent clorng of blood specimens