Carbohydrates Biochemistry Lecture PDF

CARBOHYDRATES BIOCHEMISTRY LECTURE  CARBOHYDRATES OBJECTIVES:  Classify carbohydrates and give examples for each  Know the important functions of carbohydrates in the living organism’s body  CARBOHYDRATES  The most abundant organic molecules in nature  Organic compounds...

CARBOHYDRATES BIOCHEMISTRY LECTURE  CARBOHYDRATES OBJECTIVES:  Classify carbohydrates and give examples for each  Know the important functions of carbohydrates in the living organism’s body  CARBOHYDRATES  The most abundant organic molecules in nature  Organic compounds composed of C, H & O in the ratio of 1:2:1 (CH2O)  Found primarily in plants  An excellent source of energy  FUNCTIONS  Important source of rapid energy production for living cells (ex. glucose, glycogen, starch)  They also serve as structural building blocks of cells (ex. cellulose, peptidoglycan, chitin)  Involved in cell communication and cell recognition (ex. glycoproteins, glycolipids)  FUNCTIONS  Provides fiber which make defecation a lot more easier and may prevent constipation & colon cancer  Provides nutritive and naturally occurring sweeteners (ex. honey, maple syrup, corn syrup)  Protein-sparing effect—if enough carbohydrate is provided to meet the energy needs of the body, proteins can be spared or saved to use for specific protein functions Carbohydrates (glycans) have the following basic composition: I (CH2O)n or H - C - OH I  Monosaccharides - simple sugars with multiple OH groups.  Disaccharides - 2 monosaccharides covalently linked.  Oligosaccharides - a few monosaccharides covalently linked.  Polysaccharides - polymers consisting of chains of monosaccharide or disaccharide units.  CLASSIFICATION A. Monosaccharides Simple sugars & the building blocks of carbohydrates Composed of one or single carbohydrate unit Carbohydrates that cannot be hydrolyzed or broken into simpler carbohydrate ex. glucose, fructose, galactose, ribose, deoxyribose  CLASSIFICATION A. Monosaccharides Aldoses - sugars with an aldehyde functional group (ex. glyceraldehyde) Ketoses – sugars with a ketone functional group (ex. dihydroxyacetone)  Monosaccharides Aldoses (e.g., glucose) have Ketoses (e.g., fructose) have an aldehyde group at one a keto group, usually at C2. end. H O C CH2OH H C OH C O HO C H HO C H H C OH H C OH H C OH H C OH CH2OH CH2OH D-glucose D-fructose  CLASSIFICATION A. Monosaccharides Based on number of carbons (3, 4, 5, 6), a monosaccharide is a triose, tetrose, pentose or hexose. Pentoses & hexoses are the most abundant monosaccharides found in living cells CLASSIFICATION  MONOSACCHARIDES 1. Glucose Also known as dextrose or blood sugar – the primary fuel for living cells In animals, glucose is the preferred energy source of brain cells & cells that have few or no mitochondria (ex. RBC/erythrocytes) The eyeball have cells with limited oxygen supply also use a large amount of glucose to generate energy  MONOSACCHARIDES 2. Fructose Also known as levulose – referred to as fruit sugar because of its high content in fruits It also found in vegetables as well as in honey An important member of the ketose family of sugars Twice as sweet as sucrose, thus, often used as a sweetening agent in processed food products Fructose is synthesized in the seminal vesicles of the male reproductive tract & then incorporated in the semen; sperms use this sugar as an energy source  MONOSACCHARIDES 3. Galactose Necessary for the synthesis of a variety of biomolecules such as lactose in mammary glands, glycolipids, glycoproteins & phospholipids in cell membranes, and proteoglycans in cornea, cartilages & intervertebral disks Galactosemia – a genetic disorder wherein an enzyme needed for galactose metabolism is missing; accumulation of galactose results in liver damage, cataracts, & severe mental retardation The only effective treatment for galactosemia is an early diagnosis and removal of any galactose from the diet  MONOSACCHARIDES 4. Ribose & Deoxyribose A five-carbon or pentose sugar present in a cell’s genetic material DNA and RNA DNA or Deoxyribonucleic acid – contains deoxyribose sugar; RNA or Ribonucleic acid contains ribose sugar  CLASSIFICATION B. Disaccharides Double sugar; yield two molecules of monosaccharides when hydrolyzed or broken down Provide a significant source of calories in many human diets Examples: lactose, maltose, sucrose & cellobiose  DISACCHARIDES 1. Lactose (glucose + galactose) Also known as milk sugar – a disaccharide found in milk and milk products It is composed of one molecule of glucose attached to a molecule of galactose via a beta bond Many people are unable to digest large amounts of lactose because they do not produce enough of the enzyme lactase that is capable of breaking its beta bond. This can cause intestinal gas, bloating, cramping, and discomfort as the unabsorbed lactose is metabolized into acids and gases by bacteria in the large intestine  DISACCHARIDES 2. Maltose (glucose + glucose) Also known as malt sugar It is composed of two glucose units joined by an alpha bond; an intermediate product of starch hydrolysis and does not appear to exist free in nature Sugar that provides energy for plants to initiate growth and is used in the production of alcoholic beverages such as beer  DISACCHARIDES 3. Sucrose (glucose + fructose) Also known as common table sugar, cane sugar or beet sugar It is composed of glucose and fructose linked via an alpha bond A disaccharide produced in the leaves of the plants & serve as a transportable energy source throughout the entire plant Brown, white, and powdered sugars are common forms of sucrose sold in grocery stores DISACCHARIDES  DISACCHARIDES 4. Cellobiose (glucose + glucose) It is composed of two glucose units joined by a glycosidic bond Cellobiose is a product of degradation of cellulose and is not found freely existing in nature  CLASSIFICATION C. Oligosaccharides Carbohydrates that consist of 3 to 10 monosaccharides or single sugar units Often found attached to polypeptides in glycoproteins & glycolipids of cell membranes; some are attached to membrane and secretory proteins found in endoplasmic reticulum and Golgi complex of various cells Two oligosaccharides of nutritional importance are raffinose and stachyose, which are found in beans and other legumes  CLASSIFICATION C. Oligosaccharides  CLASSIFICATION D. Polysaccharides Carbohydrate polymers containing many monosaccharide units, up to 1000 or more connected by glycosidic linkages Homopolysaccharides – composed of one type of monosaccharide; yield glucose when they are hydrolyzed Example: starch, glycogen, cellulose Heteropolysaccharides – high molecular weight carbohydrate polymers that contain more than one kind of monosaccharide; often referred to as glycosaminoglycans or GAGs Examples: hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin & heparan sulfate, and keratan sulfate  HOMOPOLYSACCHARIDES 1. Starch The energy reservoir of plant cells; stored carbohydrate in plants & is a significant source of carbohydrate in human diet Much of the nutritional value of the world’s major food stuffs consists of starch (ex. potatoes, rice, corn, and wheat) Two polysaccharides found in starch: amylose and amylopectin HOMOPOLYSACCHARIDES  HOMOPOLYSACCHARIDES 2. Glycogen The storage form of carbohydrate found in humans and other animals; a glucose polymer with alpha bonds and numerous branches It is found in greatest abundance in liver and muscle cells; glycogen make up as much as 8- 10% of the wet weight of liver and 2-3% of that of muscle cells  HETEROPOLYSACCHARIDES 1. Chondroitin sulfate An important structural component of cartilage and provides much of its resistance to compression Delivers nutrients to the joint cartilage; inhibit enzymes that decompose joint cartilage; speeds up the formation of a new joint cartilage  HETEROPOLYSACCHARIDES 2. Dermatan sulfate A glycosaminoglycan found mostly in skin, blood vessels, heart valves, tendons & lungs. Dermatan sulfate plays an important role in the structural integrity of the skin, may have roles in coagulation, cardiovascular disease, carcinogenesis, infection, wound repair, and fibrosis  HETEROPOLYSACCHARIDES 3. Heparin & Heparan sulfate Has anticoagulant activity; contains D-glucuronic acid & is found in mast cells for inflammation response and cell differentiation 4. Keratan sulfate Minor constituent of proteoglycans Found in cornea, cartilage, and intervertebral disks Important roles in corneal development; maintenance of transparency of tissue HETEROPOLYSACCHARIDES  HETEROPOLYSACCHARIDES 5. Hyaluronic acid Most abundant glycosaminoglycan in the vitreous humor of the eye, and the synovial fluid of joints To retain water to keep tissues well lubricated and moist DIGESTION & ABSORPTION OF CARBOHYDRATES  the gastrointestinal tract has the role of digesting carbohydrates into monosaccharides for easy absorption  digestion: mouth—salivary amylase/ptyalin (enzyme)  ex. starch------- dextrin, maltose  small intestine—brush border cells secrete enzymes (maltase, sucrase, lactase)  monosaccharides are then absorbed in the small intestine  CARBOHYDRATE METABOLISM  Glycogenesis - the process of converting glucose to glycogen  Glycogenolysis - the process of converting glycogen back to glucose  Gluconeogenesis - the process of producing glucose from fats and proteins BLOOD GLUCOSE REGULATION  Blood glucose is a source of energy to all cells  Glucose is essential for normal brain function and cell formation  N value= 70-120 mg/dl BLOOD GLUCOSE REGULATION  Controlled by a sophisticated hormonal system:  INSULIN- lowers blood glucose level by glycogenesis  GLUCAGON- increases blood glucose level by glycogenolysis  SOMATOSTATIN- inhibits the functions of insulin & glucagon  HYPOGLYCEMIA  low blood glucose level  is not a disease but a symptom of an underlying disorder  possible causes: o fasting, intestinal malabsorption of glucose o anti-DM drugs, overproduction of insulin by the pancreas  DIABETES MELLITUS  is a disorder of carbohydrate metabolism characterized by hyperglycemia caused by insulin that is either defective or deficient  DIABETES MELLITUS  TYPE 1 DM o a form of DM in which the pancreas produces NO insulin at all o characterized by Beta cell destruction with severe insulin deficiency, is caused by autoimmune destruction of pancreatic B cells o age of onset: < 30 years old  NOT risk related  DIABETES MELLITUS  TYPE 2 DM o a form of DM in which the pancreas produces some insulin that is defective and unable to serve the complete needs of the body o insulin resistance is the hallmark of this disorder, this means there is a decreased response to insulin by target tissues o age of onset: > 30 years old o risk related: the risk increases with family history, age, weight and caloric intake THANK YOU!