Module 5: Carbohydrates - Biochemistry - Pines City Colleges

Pines City Colleges GENERAL EDUCATION DEPARTMENT First Semester, A.Y. 2024-2025 Course Number: BIOCHEM 101 Course Title: BIOCHEMISTRY Modular Learning Guide #5 Topic: CARBOHYDRATES...

Pines City Colleges GENERAL EDUCATION DEPARTMENT First Semester, A.Y. 2024-2025 Course Number: BIOCHEM 101 Course Title: BIOCHEMISTRY Modular Learning Guide #5 Topic: CARBOHYDRATES Expected Time of Completion: 6 Hours A. Learning Outcomes 1. Discuss the nature and structure of carbohydrates 2. List the functions of carbohydrates and pathways that carbohydrates undergo in their biotransformation B. Learning Content Overview MLG 5 covers discussion about carbohydrates. This includes functions, classifications, structures, properties, and pathways. Recap/Review of the Past Lesson In MLG 1, you know biochemistry is the chemistry of life. The different chemical components of the cell were provided including their primary function and that is it is the main source of fuel or energy for metabolic activities. Concepts Nonbiologic systems use heat to perform work while biologic systems are isothermic (temperature does not change or constant temperature) and use chemical energy to power the living system. For animals, humans in particular, use adenosine triphosphate (ATP) as a source of energy. ATP is the principal high- energy intermediate or carrier compound in the cell. It plays a central role in energy capture and transfer. It is able to act as a donor of high-energy phosphate to form other compounds. CARBOHYDRATES are the main energy source for the human body. Chemically, carbohydrates are organic molecules in which carbon, hydrogen, and oxygen bond together in the ratio: Cx(H2O)y, where x and y are whole numbers that differ depending on the specific carbohydrate to which we are referring. Animals (including humans) break down carbohydrates during the process of metabolism to release energy. For example, the chemical metabolism of the sugar glucose is shown below: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy Animals obtain carbohydrates by eating foods that contain them, for example rice, breads, potatoes, and so on. These carbohydrates are manufactured by plants during the process of photosynthesis. Plants harvest energy from sunlight to run the reaction just described in reverse: 6 CO2 + 6 H2O + energy (from sunlight) → C6H12O6 + 6 O2 The term carbohydrate was derived from the terms carbon and hydrate because of the chemical. Carbohydrates however are polyhydroxy aldehydes or ketones. Polyhydroxy because the structure shows that the number of hydroxyl groups is one less that the number of carbon atoms of the sugar unit. The sugar is an aldehyde if the carbonyl group is at a terminal position or ketone if the carbonyl group is within the chain. These structures will be shown later when you reach the discussion about the classes of carbohydrates. FUNCTIONS OF CARBOHYDRATES: 1. Furnishes energy necessary to carry on the work of the body 2. They are important structural components 1|Page  3. They may be transformed into other, totally different kinds of molecules, like amino acids, lipids and nucleic acids 4. Provider of bulk roughage in the diet 5. They attach to proteins and lipids to form glycoproteins and glycolipids 6. For the storage and generation of energy – excess carbohydrates are manufactured into fatty tissue and serve as source of future fuel 7. Aids in the better functioning of the liver since a well starched liver with glycogen functions more efficiently 8. Serves as the body’s most useful emergency fuel and is the food most frequently introduced into the vein when all other venues for feeding are closed 9. Sole energy source for the brain and nerve tissues – brain and nerve tissues utilize only glucose for energy. There must be a constant supply of glucose that reaches these tissues to prevent irreversible damage to the brain. 10. A protein sparer – energy needs of the body is given first priority over body-building needs. The supply of carbohydrates must be sufficient so that protein will not be catabolized to provide heat and energy. PROPERTIES: A. Physical 1. The mono-, di- and oligosaccharides are white crystalline substances; starches are amorphous powder, while the most complex cellulose is fibrous. 2. The solubility to ordinary solvent is inversely proportional to the complexity of their structures. - Both monosaccharides and disaccharides are readily dissolved in water, however, the more complex carbohydrates like starch dissolve only slightly. Cellulose on the other hand is insoluble. 3. Mono-, di- and oligosaccharides are sweet, while polysaccharides are tasteless. SUGAR SWEETNESS RATING Fructose 1.2 – 1.8 Sucrose 1.00 Glucose 0.60 Maltose 0.50 Galactose 0.32 Lactose 0.15 – 0.30 Note: The standard for sweetness is sucrose. The other sugars are compared to its sweetness. B. Chemical 1. Reducing power – all monosaccharides and disaccharides that contain the free aldehyde or ketone group can reduce alkaline metals (this is the reason why these sugars are called reducing sugars) and these sugars are converted into organic acids a. Fehling’s test (positive result: yellow to brick red precipitate) b. Benedict’s test (positive result: yellow to brick red precipitate) c. Nylander’s test [bismuth nitrate = Bi(OH)2NO3] (positive result: black precipitate) 2. Osazone formation – reducing sugars when treated with excess phenylhydrazine (C6H5NHNH2) forms characteristic crystals 3. Action of alkalies – when a solution of reducing sugar is heated with an alkali it turns yellow then orange and finally brown 4. Action of acids – disaccharides and more complex carbohydrates are readily decomposed in the presence of an acid a. Molisch test (positive result: violet ring at the junction) b. Anthrone test (positive result: blue or green color) c. Seliwanoff’s test (positive result: red color) d. Tollen’s test (positive result: red color or silver mirror) 5. Reactions of pentoses a. Bial’s Orcinol-HCl test (positive result: green solution with precipitate) b. Tauber’s benzidine test (positive result: violet color) 6. Fermentation – sugars are fermented to produce ethyl alcohol Fermentation is the process of producing ethyl alcohol from carbohydrates. The reaction also involves the release of carbon dioxide. The process is caused by living cells (yeast) as proven by Louis Pasteur. 7. Oxidation – except sucrose, monosaccharides and disaccharides especially the aldoses are readily oxidized forming sugar acids. This is readily seen as the browning reaction of some foods. - Those that darken easily include apples, bananas, pears, potatoes, etc. 2|Page  - Those that do not darken readily include lemon, lime, orange, pineapple, etc. 8. Reduction – all sugars except sucrose undergo reduction. The reaction involves the absorption of energy and the formation of substances that are convertible into fats. 9. Esterification – sugars contain the primary alcohol group (-CH2OH) in which make these substances react with an acid to form esters CLASSIFICATIONS OF CARBOHYDRATES (based on the number of sugar units): I. MONOSACCHARIDES – those carbohydrates that cannot be hydrolyzed into simpler carbohydrates. SUBCLASSES: A. Depending on the Number of Carbon Atoms: 1. Diose – sugars with 2 carbon atoms 2. Triose – sugars with 3 carbon atoms 3. Tetrose – sugars with 4 carbon atoms 4. Pentose – sugars with 5 carbon atoms 5. Hexose – sugars with 6 carbon atoms 6. Heptose – sugars with 7 carbon atoms B. Depending on the Location of the Carbonyl Group: 1. Aldose – terminal position (carbon #1) 2. Ketose – any carbon other than the terminal Examples: ALDOSES KETOSES diose glycoaldehyde triose (C3H6O3) glycerose dihydroxyacetone tetrose (C4H8O4) erythrose erythrulose pentose (C5H10O5) ribose ribulose hexose (C6H12O6) glucose fructose heptose (C7H14O7) mannoheptose mannoheptulose II. DISACCHARIDES – those carbohydrates that yield two molecules of monosaccharides when hydrolyzed. Examples: maltose – contains 2 glucose units sucrose – contains glucose and fructose lactose – contains glucose and galactose Note: Maltose, sucrose, and lactose are made of hexose sugars only. The molecular formulae of these three are the same (C12H22O11). Though the molecular formulae are the same, the structures however differ hence called isomers. III. OLIGOSACCHARIDES – those carbohydrates that yield from three to ten monosaccharides upon hydrolysis. Examples: maltotriose – a trisaccharide (C18H32O16) of glucose. It occurs in some plants and in the blood of some arthropods (insects and crustaceans). 3|Page  raffinose – a trisaccharide (C18H32O16) of glucose, fructose, and galactose. It is found in sugar beets, cottonseed meal and molasses. stachyose – a sweet crystalline tetrasacchharide (C24H42O21) of glucose, fructose and 2 galactose units. It is found in tubers and legumes. IV. POLYSACCHARIDES – those carbohydrates that yield more than ten monosaccharides on hydrolysis. SUBCLASSES: A. According to the Type of Saccharide Present: 1. Homopolysaccharide – a polymer made up of a single type of monosaccharide. Examples: starch both are made of glucose glycogen 2. Heteropolysaccharide – a polymer made up of two or more different monosaccharides. Examples: hyaluronic acid – a polysaccharide that is abundant in the skin and soft tissue and can be isolated from umbical cord. It contributes to the lubricating effect of body fluids and serves as cementing substance (it allows the passage of metabolites but not of the infecting microorganisms) in tissues. heparin – is a polysaccharide which is a powerful inhibitor of blood clotting thus preventing intravascular coagulation. B. According to the Number of Carbon Atoms of the Saccharide: 1. Pentosans – (C5H8O4)x + H2O Examples: xylan (pentose is xylose), araban (pentose is arabinose) 2. Hexosans – (C6H10O5)x + H2O a. Glucosans (hexose is glucose) b. Fructosans (pentose is fructose) c. Mannosans (hexose is mannose) 3. Mixed Examples: gums, hemicelluloses, compound cellulose FORMS OF ISOMERISM IN SUGARS: 4|Page  1. D- and L- isomerism – the structures differ due to the location of –H and –OH around the carbon atom adjacent to the terminal primary alcohol carbon (CH2OH). For L-glycerose, the OH group on carbon#2 is on the left while it is on the right of D-glycerose. L stands for levorotatory (means rotation is to the left) while D stands for dextrorotatory (means rotatory is to the right). 2. Pyranose and furanose ring structures – the structures vary due to the number of carbon atoms in the ring pyran furan The corners of the polygons are carbon atoms except where O (oxygen) is located. Pyran has 5 carbon atoms while furan has 4. 3. Alpha and beta anomers – the structures vary due to the location of –H and –OH on carbon #1 of the ring structures alpha beta For alpha-D-glucopyranose, the OH group is below the plane while it is above the plane for beta-D- glucopyranose. 4. Aldose-ketose isomerism – the differ due to the position of the carbonyl (C=O) group dihydroxyacetone 5|Page  For D-glycerose, the carbonyl group is on carbon #1 making it an aldose while it is in carbon #2 for dihydroxyacetone, which makes it a ketose. 5. Epimers – the structures vary due to the configuration of the –H and –OH on carbon atoms which are not located at a terminal position nor the carbon adjacent to the primary alcohol group. Comparing D-glucose and D-mannose, the structures vary at carbon #2. Comparing D-glucose and D-galactose, the structures vary at carbon #4. Comparing D-Mannose and D-galactose, the structures vary at carbons #2 and #4. IMPORTANT SUGARS: 1. Glucose (also called dextrose or grape sugar) is a white or yellowish-white crystalline solid. It is the most important carbohydrate because it is as glucose that the bulk of dietary carbohydrate is absorbed into the bloodstream or into which it is converted in the liver, and it is from glucose that all other carbohydrates in the body can be formed. 2. Fructose (also called levulose or fruit sugar) is the sweetest sugar found in the free state in fruit juices, honey and nectar of plant glands. It can be changed to glucose in the liver and so used in the body. It is commercially prepared by the hydrolysis of inulin and difficult to crystallize due to its property of absorbing moisture. It is found in the urine of patients suffering from diabetes mellitus. 3. Galactose is synthesized in the mammary gland to make the lactose of milk and formed by the hydrolysis of lactose. It can be changed to glucose in the liver and metabolized. It is a constituent of glycoproteins and glycolipids and found in plants as a constituent of pectin. 4. Sucrose (also called saccharose, table sugar or cane sugar) is the major source of energy. It is the starting material for biological synthesis and plays an important role in the structure of biological compounds. It aids in the breakdown of foodstuff by acting as catalyst or as promoter of oxidation. Invert sugar is also made of glucose and fructose just like sucrose. However, it is sweeter than sucrose due to the predominance of fructose. 5. Maltose (also called malt sugar or brewer’s sugar) is a sweet, crystalline white powder. It is an intermediate product in the digestion of starch to glucose. It is easily digested which makes it an essential ingredient of food preparations for babies. 6. Lactose (also called milk sugar) is found in milk but otherwise does not occur in nature. It is about 4.5% of cow’s milk and 6.7% of human milk. Milk is considered as the most complete single food found in nature. It contains proteins, carbohydrates, fats and inorganic salts (calcium and phosphorus). Colostrum is the first milk that is produced by the mammary gland. It has high vitamin A and carotene content than ordinary milk. 7. Starch is a homopolymer called glucan or glucosan and is the most important food source of carbohydrate that is found in cereals, potatoes, legumes and other vegetables. It occurs in the form of granules (made up of 98% amylase). 8. Glycogen (also called animal starch) is the storage polysaccharide of the animal body (liver and muscle). 9. Inulin is hydrolysable to fructose, and hence it is a fructosan. It is a starch found in tubers and roots of dahlias, artichokes and dandelions and in bulbs of onions and garlic. 10. Dextrins are a group of carbohydrates that appears as amorphous, white powder. These substances are soluble in ordinary solvents but insoluble in alcohol. Dextrins are formed in the course of hydrolytic 6|Page  breakdown of starch. These compounds are used in making infant food to prevent the formation of large, heavy curds of milk to facilitate digestion. 11. Chitin is an important structural polysaccharide of invertebrates. It is found in the exoskeletons of crustaceans and insects. 12. Cellulose is the chief constituent of the framework of plants. It is an important source of “bulk” in the diet. It is insoluble and indigestible to many mammals, including humans, because of the absence of a hydrolase that attacks the β linkage. It forms part of dietary fiber and the purest source is cotton. CARBOHYDRATE METABOLISM Carbohydrate metabolism starts with glucose-6-phosphate. The important pathways that stems from glucose-6-phosphate are the following: a. Glycolysis (anaerobic) in the Embden Meyerhof Pathway b. Kreb’s Cycle (aerobic) c. Hexose monophosphate shunt d. Conversion to glycogen e. Conversion to fat f. Excretion through the urine Glycolysis is the major pathway for the utilization of glucose and is found in the cytosol of all cells. It is a unique pathway because it may use oxygen (aerobic) or it can proceed without oxygen (anaerobic). There are major steps involved in anaerobic glycolysis (also called Embden Meyerhof Pathway). The first step involves the phosphorylation and cleavage of glucose. The second step is the conversion of glyceraldehyde-3-phosphate into lactic acid. The aerobic process called Kreb’s Cycle (also known as Tricarboxylic Acid Cycle) involves a series of reactions that takes place in the mitochondria to bring about the catabolism of acetyl residues. Acetyl residues when catabolized releases hydrogen residues and when oxidized it leads to the release and capture of ATP. The acetyl residues used in the cycle may be derived not only from carbohydrates but also from lipids, and amino acids. Other possible conversion processes are the following: Glucogenesis is the process used in the conversion of non-glucose hexose (fructose, galactose, etc.) into glucose so that it can participate in glycolysis. Glycogenesis is the process used in the formation of glycogen from glucose units. Glucose undergoes phosphorylation with uridine diphosphate. Uridine diphosphate molecules unite to form glycogen. Glycogenolysis is the process used to break down stored glycogen into glucose units to provide energy. Glyconeogenesis is the process of converting non-carbohydrate substances (especially proteins or amino acids) into carbohydrate substrates. C. Learning Activities This group activity will be equivalent to 50 points. Make a collage that depicts the function of carbohydrates. The collage will be made on a whole piece of cartolina using pictures of foods that contain carbohydrates, which you can cut from old magazine and newspapers. CATEGORY 10 8 6 3 CREATIVITY All of the graphics or Most of the graphics or Only a few graphics or None of the graphics or objects used in the objects used in the objects reflect students objects reflects student collage reflect creativity collage reflect student creativity, but the ideas creativity. in their display. creativity in their were typical rather than Students utilize display. creative. numerous materials for texture. DESIGN Graphics are cut to an 1-2 graphics are lacking 3-4 graphics are lacking Graphics are not an appropriate size, shape in design or placement. in design or placement. appropriate size shape. and are arranged There may be a few Too much background Glue marks evident. neatly. Items are glued smudges or glue is showing. There are Most of the background neatly and securely. NO marks. No tape marks noticeable smudges or is showing. It appears FRAYED EDGES! No are obvious from the glue marks. little attention was given 7|Page  tape is showing from front. to designing the the front! collage. TIME AND EFFORT Much time and effort Time was used wisely, It appears the students Class time was not went into the planning but students could have didn’t put in a lot of used wisely and the and design of the put in more time and effort before the students put in no collage. It is clear the effort at home. Project presentation. The additional effort. students worked at was complete but only project is unfinished or home as well as at showed the basics. completed without school. color. TITLES AND TEXT Titles and text were Titles and text were Titles and text were Titles and/or text are written clearly and were written clearly and were mostly clear and hard to read, even easy to read from a easy to read close-up. somewhat easy to read when the reader is distance. NO Possible minor spelling close-up. close. Spelling or SPELLING OR and grammar errors. Many spelling and grammar errors are GRAMMAR ERRORS! grammar errors. distracting. ATTENTION TO THEME The students give a The students give The student gives a The students reasonable explanation explanation of how fairly reasonable explanations are weak of how every item in the most items in the explanation of how and does not illustrate collage is related to the collage are related to most items in the how to relate items to lesson. the lesson. collage are related to the lesson. the lesson. D. Resources 1. What are Carbohydrates? https://www.livescience.com/51976-carbohydrates.html 2. What you need to know about carbs https://www.medicalnewstoday.com/articles/161547#what-are-carbohydrates 3. Types of Carbohydrates https://www.diabetes.org/nutrition/understanding-carbs/types-carbohydrates E. Assessment Prepare for a 25-point quiz next meeting. F. References Harvey, Richard and Denise Ferrier. (2017). Lippincott’s Illustrated Reviews: Biochemistry (7th edition). U.S.A.: Wolters Kluwer. Murray, Robert K. et al. (2015). Harper’s Illustrated Biochemistry (30th edition). U.S.A.: McGraw-Hill Book Company. Prepared by Cecilia L. Cabanilla Instructor 8|Page