BIOCHEMISTRY Carbohydrates

Transcription

1 BICHEMISTRY Carbohydrates BIB111 CHEMISTRY & BICHEMISTRY Session 11

2 Key concepts: session 11 From this session you are expected to develop an understanding of the following concepts: Concept 1: Classes of carbohydrates: monosaccharides, disaccharides and polysaccharides Concept 2: Interpreting the names of simple carbohydrates Concept 3: Location of the functional groups in an aldoses and ketoses Concept 4: Cyclic and acyclic sugar structures Concept 5: Glycosidic bonds Concept 6: Breaking down multi-subunit sugars Concept 7: Cellulose in the diet Concept 8: Digestion of polysaccharides vs disaccharides/monosaccharides Concept 9: Glycogen These concepts are covered in the Conceptual multiple choice questions of tutorial 11

3 Session verview Part 1: Monosaccharides Classes of carbohydrates Straight-chain monosaccharides Monosaccharide: glucose Monosaccharide: galactose Monosaccharide: fructose Monosaccharides in DNA and RNA Cyclic monosaccharides Part 2: Disaccharides Glycosidic bond Digestion of dietary carbohydrates Disaccharide: Maltose Disaccharide: Lactose Disaccharide: Sucrose Part 3: Polysaccharides Digestible vs non-digestible polysaccharides Polysaccharide: glycogen

4 Part 1: Monosaccharides Classes of carbohydrates Straight-chain monosaccharides Monosaccharide: glucose Monosaccharide: galactose Monosaccharide: fructose Monosaccharides in DNA and RNA Cyclic monosaccharides

5 Functional groups in carbohydrates

6 Classes of carbohydrates Plants produce carbohydrates via photosynthesis Plants utilise carbohydrates for: Structural support (e.g. cellulose) Energy (e.g. glucose and starch)

7 Classes of carbohydrates Functions of Carbohydrates: Can be metabolised to generate energy for plants and animals Form supportive structures in plants (cellulose), insects and crustaceans (chitin) Provide short-term energy storage in plants (starch) and humans (glycogen) Carbohydrates are: Important components of DNA and RNA molecules Structural components of cell membranes (glycolipids) Involved in cell cell and cell molecule recognition processes (glycoproteins)

8 Classes of carbohydrates Glucose Single sugar unit Monosaccharide: A single unit sugar is a monosaccharide Glucose Glucose Disaccharide: A compound made up of two sugar units is a disaccharide Two sugar unit compound Polysaccharide: A compound consisting of Between 100 and 1 million sugar units is a polysaccharide Many, many sugar unit compound

9 Classes of carbohydrates Monosaccharide: A single unit sugar is a monosaccharide Examples: Glucose Fructose Galactose Glucose Single sugar unit Functions: Monosaccharides connect together via glyosidic bonds to create multi-unit sugars (disaccharides and polysaccharides) Monosaccharides can be metabolised by humans to generate ATP (cellular energy)

10 Classes of carbohydrates Glucose Glucose Disaccharide: A compound made up of two sugar units is a disaccharide Examples: Maltose Lactose Sucrose Two sugar unit compound Glucose Glucose Glucose Galactose Glucose Fructose Functions: In a disaccharide, the two sugar units are connect via a glyosidic bond Disaccharides can be broken down into two individual monosaccharides The monosaccharides can be metabolised to generate ATP (cellular energy)

11 Classes of carbohydrates Polysaccharide: A compound consisting of between 100 and 1 million sugar units Examples: Many, many sugar unit compound Starch Cellulose Chitin Glycogen Glycogen is an energy storage compound that is found in the liver and muscle Potatoes are a starch rich food Starch is made up of many glucose units which are slowly released into the blood as digestion occurs Cellulose provides structural support to plants Chitin is found in the exoskeletons of insects Glycogen is broken down into glucose units at the beginning of a run to provide quick energy generation

12 Straight-chain monosaccharides Straight-chain monosaccharides contain many alcohol groups The straight-chain monosaccharides contain either a single ketone or aldehyde group Monosaccarides that contain the aldehyde functional group are called Aldoses Example: Aldohexose is a 6 carbon monosaccharide with an aldehyde functional group Monosaccarides that contain the ketone functional group are called ketoses Example: Ketopentose is a 5 carbon monosaccharide with a ketone functional group

13 Straight-chain monosaccharides Where is the non-alcohol functional group located in the compound? At the top of the compound What is the non-alcohol functional group present in the compound? The aldehyde functional group Is the carbohydrate an aldose or a ketose? The monosaccharide is an aldose (contains the aldehyde functional group) The compound contains 6 carbons The compound is glucose

14 Straight-chain monosaccharides Where is the non-alcohol functional group located in the compound? Near the top compound between two carbon atoms What is the non-alcohol functional group present in the compound? The ketone functional group What class of carbohydrates does the compound belong to? The monosaccharide is a ketose (contains the ketone functional group) The compound contains 6 carbons The compound is fructose

15 Straight-chain monosaccharides Some compounds including glucose can exist either in a right-handed (D) or left-handed (L) isomer Both the L and D isomers are called stereoisomers Stereoisomers are the mirror image of each other at a specific position within the compound The right handed isomer is called the D isomer D-Glucose The left handed isomer is called the L isomer L-Glucose Dextrorotatory compound: A chiral compound that rotates the plane of polarized light clockwise (to the right) Levorotatory compound: A chiral compound that rotates the plane of polarized light counterclockwise (to the left) Right-hand side Note: L-glucose is not found in nature but can be created in the laboratory Left-hand side

16 Attempt Socrative questions: 1 to 4 Google Socrative and go to the student login Room name: City name followed by 1 or 2 (e.g. PERTH1) 1 for 1 st session of the week and 2 for 2 nd session of the week

17 Monosaccharide: glucose Straight chain D-glucose is an aldohexose Contains an aldehyde functional group and six carbon atoms D-glucose is the most abundant monosaccharide in nature Glucose The body relies on glucose to perform many metabolic reactions including glycolysis Metabolic reactions are required to generate cellular energy (ATP) Carbohydrate containing foods are the body s main source of glucose The body can make glucose from pyruvate and oxaloacetate using gluconeogenesis D-Glucose

18 Monosaccharide: glucose Glucose The level of glucose in the blood (blood glucose) must be maintained within a fine range: mmol/l of blood The blood glucose level is maintained by the hormone pair insulin and glucagon Glucose is delivered to the organs and tissues via the blood to allow the cells to generate energy The brain is very dependent on glucose as it cannot create energy from lipid (fats and oils) D-Glucose

19 Monosaccharide: glucose G = Glucose Insulin Insulin functions to bring glucose into the cell from the blood Insulin assists in lowering the blood glucose level when the blood glucose level is high Blood G Glucagon G Cell G Glucagon Glucagon functions to move glucose out of the cells into the blood Glucagon assists in increasing the blood glucose level when the blood glucose level is low Insulin promotes metabolic reactions that use glucose G Insulin Glucagon promotes metabolic reactions that make glucose

20 Monosaccharide: galactose Galactose Straight chain D-galactose is an aldohexose just like glucose Contains an aldehyde functional group and six carbon atoms nly difference between galactose and glucose is the position of one alcohol group D-Galactose D-Glucose

21 Monosaccharide: galactose D-Galactose is a component of the glycoprotein responsible for the AB blood groups Galactose The glycoprotein is present on the outside of the red blood cells (RBCs) If an individual who has type A blood was given type B blood, the individuals immune system would attack the new RBCs The B antigens on the RBCs are recognised by the immune system as non-self

22 Monosaccharide: fructose Fructose Straight-chain D-Fructose is a Ketohexose Contains a ketone functional group and six carbon atoms D-Fructose

23 Monosaccharide: fructose Fructose D-Fructose is the sweetest tasting sugar Found in fruit and honey within the disaccharide sucrose Sucrose contains one fructose and one glucose D-Fructose cannot be stored by the body Sucrose Fructose is metabolised by the liver Excess fructose can cause the accumulation of fat (triacylglycerol in the liver) ccurs via the lipogenesis pathway Glucose Fructose

24 Monosaccharides in DNA and RNA Both DNA and RNA contains sugar units (monosaccharides) A single unit of DNA and RNA is called a nucleotide A nucleotide contains: ne sugar (ribose or deoxyribose) A nitrogen containing base A phosphate (polyatomic ion)

25 Monosaccharides in DNA and RNA Sugar present in RNA Ribose Sugar present in DNA Deoxyribose Contains one less oxygen atom than the ribose sugar

26 Cyclic monosaccharides Monosaccharides with 5 or more carbon atoms can exist in either a: Straight-chain structure Cyclic structure Cyclic D-Glucose Straight-chain D-Glucose

27 Cyclic monosaccharides Straight-chain sugars lose their aldehyde and ketone functional groups when they become cyclical sugars Cyclical sugars contain the ether functional group Ketone Ether Aldehyde Ether Straight-chain D-Fructose Cyclic D-Fructose Straight-chain D-Glucose Cyclic D-Glucose

28 Part 1: Monosaccharides Classes of carbohydrates Single sugar units are called monosaccharides Disaccharides contain two sugar units connected together Polysaccharides contain between 100 and 1 million connected sugar units Straight-chain monosaccharides Aldoses contain the aldehyde functional group Ketoses contain the ketone functional group Straight-chain monosaccharides can exist as either an L or D-isomer, with the L-isomer being the left-handed version and the D-isomer the right-handed version Monosaccharide: glucose Straight-chain glucose is a six carbon containing aldose sugar The body relies on glucose to generate cellular energy via metabolic pathways The hormones insulin and glucagon maintain the level of glucose in the blood within a specific range Insulin lowers the blood glucose level by moving glucose out of the blood into the cells Glucagon increases the blood glucose level by moving glucose out of the cells into the blood

29 Part 1: Monosaccharides Monosaccharide: galactose Straight-chain galactose is a six carbon containing aldose sugar which has a very similar structure to glucose Galactose is present within the antigens on our red blood cells responsible for the AB blood group system Monosaccharide: fructose Straight-chain fructose is a six carbon containing ketose sugar Fructose is the sweetest sugar

30 Part 1: Monosaccharides Monosaccharides in DNA and RNA Each individual unit of DNA and RNA is called a nucleotide Each nucleotide contains either a ribose or deoxyribose sugar The only difference between ribose and deoxyribose is that deoxyribose contains one less oxygen atom Cyclic monosaccharides Monosaccharides with 5 or more carbons can exist as either a cyclic or straight-chain structure Cyclic sugars contain the ether functional group instead of an aldehyde or ketone functional group (present in straight-chain sugars)

31 Part 2: Disaccharides Glycosidic bond Digestion of dietary carbohydrates Disaccharide: Maltose Disaccharide: Lactose Disaccharide: Sucrose

32 Glycosidic bond Glyosidic bond formation Two cyclic monosaccharide sugar units connect together in a chemical reaction, where an alcohol group from one unit reacts with an alcohol group from the other unit: Alcohol + alcohol ether The ether functional group connects the two monosaccharides together to form a disaccharide CH 2 CH 2 CH 2 Glycosidic bond CH 2 + H H H Glucose Glucose Maltose H 2 + H H

33 Glycosidic bond Animation of glycosidic bond formation H H H CH 2 Glycosidic bond connecting the two glucose units together Ether H Glucose Maltose disaccharide + H CH 2 Glucose

34 Digestion of dietary carbohydrates STARCH SUCRSE LACTSE MALTSE Common dietary carbs Dietary carbohydrates TRAFFICKED T THE LIVER CELLS T BE METABLISED INT CELLULAR ENERGY (ATP) Digestive enzymes facilitate the breakdown of the dietary carbs into monosaccharides by breaking the glycosidic bonds which connect their sugar units MNSACCHARIDES: GLUCSE, FRUCTSE AND GALACTSE Glucose, galactose and fructose NLY MNSACCHARIDES ARE ABSRBED INT THE BLD VIA THE SMALL INTESTINE TRAFFICKED T THER CELL TYPES INCLUDING THE BRAIN AND MUSCLE T BE METABLISED INT CELLULAR ENERGY (ATP) Glucose

35 Disaccharide: Maltose D-maltose = D-glucose + D-glucose Two glucose units connected via a glycosidic bond forms maltose Maltose is produced during the breakdown of starch in the digestive system Maltose Glucose Glucose

36 Disaccharide: Maltose D-maltose = D-glucose + D-glucose Maltose is broken down into two glucose units in a chemical reaction facilitated by the maltase enzyme The maltase enzyme is present in the small intestine nce maltose has been broken down into two glucose units in the small intestine: The glucose is absorbed into the blood and trafficked to cells for metabolism H CH 2 Maltose CH 2 + H H H 2 Maltase H CH 2 Glucose + H CH 2 Glucose

37 Disaccharide: Maltose Animation of the breakdown of maltose Glucose Glucose H CH 2 H H CH 2 H H Maltose disaccharide ne alcohol functional group created on each glucose unit

38 Disaccharide: Lactose D-Lactose = D-Galactose + D-Glucose The galactose and glucose units within lactose are connected via a glycosidic bond Lactose is commonly found in milk Lactose Glucose Galactose

39 Disaccharide: Lactose D-Lactose = D-Galactose + D-Glucose Lactose is broken down into one galactose and one glucose in a chemical reaction facilitated by the lactase enzyme The lactase enzyme is present in the small intestine nce lactose has been broken down into one galactose and one glucose in the small intestine: The monosaccharides are absorbed into the blood and trafficked to the liver cells for metabolism H CH 2 Lactose CH 2 + H H H 2 Lactase H CH 2 Glucose + CH 2 H Galactose

40 Disaccharide: Lactose Animation of the breakdown of lactose Galactose Glucose H CH 2 H H CH 2 H H Lactose disaccharide An extra alcohol functional group is created on galactose and glucose

41 Lactose intolerance: Individuals who produce less lactase enzyme (in the small intestine) do not breakdown lactose efficiently For a lactose intolerant person, some lactose will pass through the small intestine undigested In the large intestine bacteria breakdown the lactose producing lactic acid and gas which cause cramping, nausea and diarrhea Causes of reduced amount of lactase enzyme: Genetic mutation in the gene that produces the lactase enzyme Injuries to intestinal mucosa where the lactase enzyme is produced H CH 2 Lactose CH 2 + H H H 2 Low amount of Lactase Limited conversion of lactose into monosaccharides H CH 2 Glucose + CH 2 H Galactose

42 Disaccharide: Sucrose D-Sucrose = D-Fructose + D-Glucose The fructose and glucose units within sucrose are connected via a glycosidic bond Sucrose is the sweetest sugar found in fruit and honey Table sugar is made up of sucrose The body cannot store fructose so it must be metabolised by the liver Some of the fructose is converted into: Glucose Triacylglycerol (Fat) Sucrose Glucose Fructose

43 Disaccharide: Sucrose D-Sucrose = D-Fructose + D-Glucose Sucrose is broken down into one fructose and one glucose in a chemical reaction facilitated by the sucrase enzyme The sucrase enzyme is present in the small intestine nce sucrose has been broken down into one fructose and one glucose in the small intestine: The monosaccharides are absorbed into the blood and trafficked to the liver cells for metabolism H CH 2 CH 2 H Sucrose CH 2 + H H H 2 Sucrase H CH 2 Glucose + CH 2 H H CH 2 Fructose

44 Disaccharide: Sucrose Animation of the breakdown of sucrose H Glucose CH 2 H H CH 2 H Sucrose disaccharide H CH 2 Fructose An extra alcohol functional group is created on fructose and glucose H H

45 Key concept: Formation and breakage of glycosidic bonds Describe the chemical reaction where one glucose and one fructose connect together to form the disaccharide sucrose. Can the dislufide bond that connects the two monosaccharides within sucrose be broken? If so how? Why might it be useful to break sucrose down into two individual monosaccharide units?

46 Attempt Socrative questions: 5 to 7 Google Socrative and go to the student login Room name: City name followed by 1 or 2 (e.g. PERTH1) 1 for 1 st session of the week and 2 for 2 nd session of the week

47 Part 2: Disaccharides Glycosidic bond A glycosidic bond is formed between two sugar units in a chemical reaction, allowing two individual sugar units to form one compound (a disaccharide) To form a glycosidic bond there is a reaction between two alcohol groups in two different sugar units nce a glycosidic bond has formed, an ether functional group is present at the location of the glycosidic bond Digestion of dietary carbohydrates Digestive enzymes facilitate the breakdown of dietary carbohydrates by cleaving the glycosidic bonds which connect sugar units together nly monosaccharides can be absorbed by the small intestine into the blood nce in the blood, monosaccharides are delivered to specific cell types to be metabolised into cellular energy (ATP)

48 Part 2: Disaccharides Disaccharide: Maltose Maltose is made up of two glucose units connect by a glycosidic bond The maltase enzyme facilitates the breakdown of maltose into two individual glucose units Disaccharide: Lactose Lactose is made up of one galactose and one glucose connect by a glycosidic bond The lactase enzyme facilitates the breakdown of lactose into one galactose and one glucose Lactose intolerant individuals produce less lactase enzyme, so they are less efficient at breaking down lactose during digestion Disaccharide: Sucrose Sucrose is made up of one fructose and one glucose connect by a glycosidic bond The sucrase enzyme facilitates the breakdown of sucrose into one fructose and one glucose Table sugar is made up of sucrose

49 Part 3: Polysaccharides Digestible vs non-digestible polysaccharides Polysaccharide: glycogen

50 Digestible vs non-digestible polysaccharides Many, many sugar unit compound Polysaccharide: A compound made up of 100 to 1 million sugar units is a polysaccharide Examples: Starch, glycogen, cellulose and chitin Starch Cellulose Chitin Glycogen Glycogen is an energy storage compound that is found in the liver and muscle Potatoes are a starch rich food Starch is made up of many glucose units which are slowly released into the blood as digestion occurs Cellulose provides structural support to plants Chitin is found in the exoskeletons of insects Glycogen is broken down into glucose units at the beginning of a run to provide quick energy generation

51 Digestible vs non-digestible polysaccharides Many, many sugar unit compound Polysaccharides are contain many, many monosaccharide units connected via glycosidic linkages Distinctive features of different polysaccharides: The identity of the monosaccharide monomer within the polysaccharide Length of chain varies from few hundred sugar units up to 1 million sugar units Degree of chain branching with the polysaccharide

52 Digestible vs non-digestible polysaccharides THE BDY LACKS THE ENZYME REQUIRED T BREAKDWN CELLULSE INT INVIDUAL GLUCSE UNITS Consequence Why? CELLULSE After eating a cellulose containing food CELLULSE PASSES THRUGH THE MUTH, STMACH AND SMALL INTESTINE UNDIGESTED Definition PLYSACCARIDE CMPSED F MANY CNNECTED GLUCSE UNITS N NUTRITINAL VALUE FRM CELLULSE AS IT CANNT BE ABSRBED BY THE SMALL INTESTINE Consequence CELLULSE ENTERS THE LARGE INTESTINE WHERE IT ASSISTS WITH EXCRETIN F SLID WASTE

53 Digestible vs non-digestible polysaccharides STARCH Consequence After eating a starch containing food α-amylase ENZYME BREAKS DWN STARCH INT MANY GLUCSE UNITS Definition PLYSACCARIDE CMPSED F MANY CNNECTED GLUCSE UNITS GLUCSE UNITS DERIVED FRM STARCH ARE ABSRBED BY THE SMALL INTESTINE Glucose TRAFFICKED T THER CELL TYPES INCLUDING THE LIVER, BRAIN AND MUSCLE T BE METABLISED INT CELLULAR ENERGY (ATP)

54 DIGESTABLE PLYSACCHARIDES DISACCHARIDES AND MNSACCHARIDES PLYSACCHARIDES CNTAIN MANY GLYCSIDIC BNDS MANY GLYCSIDIC BNDS T BREAK WITHIN THE PLYSACCHARIDE DISACCHARIDES CNTAIN NE GLYCSIDIC BND AND MNSACCHARIDES CNTAIN N GLYCSIDIC BNDS SLW ABSRPTIN F THE MNSACCHARIDES RELEASED FRM THE PLYSACCHARIDE DURING DIGESTIN SLW RELEASE F GLUCSE INT THE BLD Due to FEW R N GLYCSIDIC BNDS T BREAK Due to FAST ABSRPTIN F MNSACCHARIDES AND DISACCHARIDES DURING DIGESTIN FAST RELEASE F GLUCSE INT THE BLD, CAUSING A SPIKE

55 Polysaccharide: glycogen Glycogen is a polysaccharide consisting of up to 1 million glucose units In humans glycogen is stored in the liver and muscle When required glycogen is broken down into glucose units which can be metabolised to generate ATP

56 Polysaccharide: glycogen Excess glucose in the blood, after digestion of dietary carbohydrates, results in the production of glycogen (glycogenesis) Glycogen functions as a glucose storage component A low blood glucose level stimulates the breakdown of glycogen into individual glucose units (glycogenolysis) Glucose units can then be metabolised into cellular energy (ATP) Glycogenolysis Glucose storage in the liver and muscle Glycogen 1 million glucose units ATP generation from glucose Glycogenesis

57 Key concept: digestible vs non-digestible carbohydrates Why can humans digest starch but not cellulose? Why is it necessary to breakdown dietary carbohydrates into monosaccharides during digestion? If there is excess glucose after digestion, what will the excess glucose be used for?

58 Attempt Socrative questions: 8 to 10 Google Socrative and go to the student login Room name: City name followed by 1 or 2 (e.g. PERTH1) 1 for 1 st session of the week and 2 for 2 nd session of the week

59 Part 3: Polysaccharides Digestible vs non-digestible polysaccharides Cellulose cannot be digested by humans, as humans lack the enzyme required to break the glycosidic bonds present in cellulose Cellulose provides no nutritional value to humans but it does help with excretion of solid waste Starch can be digested by humans, as humans have the α-amylase enzyme required to break the glycosidic bonds present in starch The glucose units released from the digestion of starch are trafficked to cells (via the blood) to generate cellular energy (ATP) The more glycosidic bonds a sugar contains the slower it is digested Starch is digested slowly and consequently releases glucose into the blood slowly Disaccharides and monosaccharides are digested quickly and can cause the blood glucose level to increase rapidly Polysaccharide: glycogen Glycogen is a polysaccharide consisting of up to 1 million glucose units Glycogen is stored in the liver and muscle Glycogen is created from glucose when glucose is in excess (glycogenesis) Glycogen is broken down into glucose when blood glucose is low (glycogenolysis)

60 Readings & Resources Stoker, HS 2014, General, rganic and Biological Chemistry, 7 th edn, Brooks/Cole, Cengage Learning, Belmont, CA. Stoker, HS 2004, General, rganic and Biological Chemistry, 3 rd edn, Houghton Mifflin, Boston, MA. Timberlake, KC 2014, General, organic, and biological chemistry: structures of life, 4 th edn, Pearson, Boston, MA. Alberts, B, Johnson, A, Lewis, J, Raff, M, Roberts, K & Walter P 2008, Molecular biology of the cell, 5 th edn, Garland Science, New York. Berg, JM, Tymoczko, JL & Stryer, L 2012, Biochemistry, 7 th edn, W.H. Freeman, New York. Dominiczak, MH 2007, Flesh and bones of metabolism, Elsevier Mosby, Edinburgh. Tortora, GJ & Derrickson, B 2014, Principles of Anatomy and Physiology, 14 th edn, John Wiley & Sons, Hoboken, NJ. Tortora, GJ & Grabowski, SR 2003, Principles of Anatomy and Physiology, 10 th edn, John Wiley & Sons, New York, NY.

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