Introduction to Biochemistry - Carbohydrates - PDF

**The Study of Living Things** **Biochemistry** is the systematic study of the chemical substances found in living organisms, their organization & chemical interactions with each other, and the principles of their participation in the processes of life. Its importance is due to the increasing...

**The Study of Living Things** **Biochemistry** is the systematic study of the chemical substances found in living organisms, their organization & chemical interactions with each other, and the principles of their participation in the processes of life. Its importance is due to the increasing recognition that underlying each and every biological function is a chemical reaction. Hundreds/thousands of chemical reactions are taking place in our cells every minute of our lives. Biochemical investigations have been directed towards the study of the chemical composition of cells and the chemical processes in which they participate. A **biochemical substance** is a chemical substance found within a living organism. **Two types of biochemical substances:** 1.**Bioinorganic substances:** water and inorganic salts. 2.**Bioorganic substances:** carbohydrates, lipids, proteins, and nucleic Acids As isolated compounds, bioinorganic and bio organic substances have no life in and of themselves. Yet when these substances are gathered together in a cell, their chemical interactions are able to sustain life. A cell in particular, and a whole organism in general, has three basic needs: materials, information, and energy. Without the daily satisfaction of these, human life would be severely constrained.  **Main classes of foodstuffs - Materials** The bioorganic materials of life will be considered, starting with the three main classes of foodstuffs **carbohydrates, lipids, and proteins.** Humans use these molecules to build and run their bodies and to try to stay in some state of repair. Plants rely heavily on **carbohydrate** for cell walls, and animals obtain considerable **energy** from carbohydrates made by plants. **Lipids** serve many purposes. They are used, both by plants and animals, as materials to make cell membranes and as sources of chemical energy.  **Proteins** are particularly important in both the structures and functions of cells  Because of the catalytic role of proteins in regulating chemical events in cells, the study of proteins will be immediately followed with an examination of enzymes, which make up a particular family of proteins. **Information System** Every cell has an information system- **enzymes, hormones, and neurotransmitters** are components of the intricate information system in the body. Without information, the **materials and energy** delivered to the body could produce only rubbish. Although enzymes are major players in the cells\' information system, they do not originate the cellular script. They only help to carry out directions that are encoded in the molecular structures of the nucleic acids, which are compounds that are able to direct the synthesis of enzymes. Thus the study of the enzyme makers, the nucleic acids, is included in any study of the molecular basis of life. -Hormones & neurotransmitters, two other components of cellular information, depend on the presence of right enzymes not only for their existence but for their functions. **Biochemical substances** To supply materials for any use parts, information, or energy - each organism has basic nutritional needs. These include not just bioorganic materials, including vitamins, but also bio inorganic materials including minerals, water, and oxygen. Thus, together with learning about the bioorganic materials of life and how they are processed and used, the need for vitamins, minerals, water, and oxygen will also be considered. **CELL STRUCTURE** Based on their cell structures, organisms ARE divided into TWO main groups: **Prokaryotes** **Greek - meaning \"BEFORE the nucleus\"; singlecelled organisms** \- about **10 times SMALLER than eucaryotic cells** \- A typical Escherichia coli cell is about 1 um wide and 2 to 3 um long **Eukaryote** **Greek - meaning \"true nucleus\".** **Most animal and plant cells are 10 to 30 um in diameter, about 10 times larger than most procaryotic cells.** contain a well-defined nucleus surrounded by a nuclear membrane can be single celled, such as yeasts and Paramecium, or multicellular, such as animals and plants **FIVE KINGDOMS** **Monera** - prokaryotic organisms; includes bacteria and cyanobacteria **Protista** - unicellular eukaryotes: yeast, Euglena, Volvox, Amoeba, and Paramecium **Fungi** - molds and mushrooms **Plantae** ** Animalia** Fungi, plants, and animals are multicellular eukaryotes (with few unicellular eukaryotes) **The Study of Living Things - The CELL STRUCTURE** The main difference between prokaryotic and eukaryotic cells is the existence of **organelles**, especially the nucleus, in eukaryotes. An **organelle** is a part of the cell that has a distinct function; it is surrounded by its own membrane within the cell.  **CELL MEMBRANE** a **semi-permeable** membrane surrounding the cell separating it's internal environment from the external environment. permits and/or enhances the absorption of essential nutrients into the cell while preventing the diffusion of needed metabolites.  a lipid bilayer that mechanically holds cell together. **Component biomolecules:** 1.Lipids: phospholipids, cholesterol 2.Proteins 3.Carbohydrates Lipids provide the basic structure of biological membranes. Proteins are embedded in the membranes and provide channels/carriers for the transport of ions and nutrients. **CYTOPLASM** structureless and highly viscous the aqueous phase of the cell in which many particulate constituents like mitochondria, ribosomes, etc. Are suspended contains a wide variety of solutes including proteins, enzymes, nucleic acids (RNA), a number of electrolytes, metabolites for cellular utilization (e.g.,glucose), and waste products of cellular activity (e.g., urea, creatinine, uric acid,etc.) **NUCLEUS** The nucleus the \"information center\" of the cell; enclosed by a nuclear membrane and contains the cells genetic information and the machinery for converting that information into protein molecules. site of DNA and RNA synthesis. contains a comparatively large amount of nucleoprotein (50% DNA and 50% proteins, histones and prolamines located in the chromosomes, and a small amount of RNA; \>95% of nucleic acids of the cell is in the nucleus nucleolus, - small, round dense body present within the nucleus; not surrounded by membrane; essentially a cluster of looped chromosomal segments; contains 10-20% of the total RNA of the cell, chiefly mRNA serve as a storehouse for mRNA prior to its movement into the cytoplasm by way of the nuclear pores **MITOCHONDRIA** the second largest organelle the powerhouse of the cell where carbohydrates, lipids, and amino acids are oxidized to CO2 and H2O by molecular O2 and the energy set free is converted into the energy of ATP has a double -membrane structure, an outer membrane and an inner membrane Site for cellular respiration The inner membrane, in which the enzymes of electron transport and energy conversion are located, is convoluted to form shelves termed cristae. **ENDOPLASMIC RETICULUM** appears to be a system of interconnected tubules or canaliculi extending throughout the cell cytoplasm and is. continuous with the outer nuclear membrane two types: rough and smooth er **rough er** is lined with a numbe of small, spheric, electron-dense particles called ribosomes -primarily involved in synthesis of membrane proteins and proteins for export from the cell **smooth er** lacks ribosomes appears to be involved inthe biosynthesis of steroids, phospholipids, and complex polysaccharides functions also include biotransformation, a process in which water- soluble organic molecules are prepared for excretion **RIBOSOME** consist of \~50% RNA (rRNA) and 50% protein involved in protein synthesis in the cell and are sometimes referred to as the \"workbench\" for protein synthesis complex structures containing two irregularly shaped subunits of unequal size they come together to form whole ribosomes when protein synthesis is initiated when not in use, the ribosomal subunits separate **The golgi apparatus / golgi complex** structures composed of flattened sacs with vesicles, located near the nucleus, probably continuous with er the organelles to which synthesized proteins are transported and temporarily stored before release from the cell the \"packaging stations\" of the cell he primary site for packaging and distribution of cell products to internal and external compartments there is a continuous flow of substances through the Golgi apparatus responsible for sorting and packaging several types of proteins, small molecules, and new membrane components **LYSOSOMES** An Overview The lysosomes membrane -bound organelles containing a variety of hydrolytic and degradative enzymes and having an optimum pH of 5.0 has regulatory and defense function function in the digestion of materials brought into the cell by phagocytosis and pinocytosis also serve to digest cell components after cell death also serve to digest cell components after cell death the \"suicide bags\" of the cell upon death of the cell or its exposure to environmental conditions, the lysosomal membrane disintegrates, releasing its contents, which cause the self-digestion or autolysis of the cell constituents **PEROXISOMES** contains oxidative enzymes that oxidize amino acids, uric acid, and various 2- hydroxyamino acids using O2 with the formation of H2O2 H2O2 is then converted to H2O and O2 by the enzyme catalase also present in the peroxisomes thus the cell protects itself from the toxicity of H2O2 The Solvent the agency that enables water-soluble, water-miscible, or emulsifiable substances to be transferred in the body not only in the blood but also intercellularly and intracellularly  **Biochemical reactions** ionization is a prerequisite to many biochemical reactions and ionization takes place in water **Physiologic regulation of body temperature** **high specific heat** (amount of heat required to raise the temperature of 1g of H2O 1°C) enables the body to store heat effectively without greatly raising its temperature **high heat conductivity** permits heat to be transferred readily from the interior of the body to the surface **high latent heat of evaporation** causes a great deal of heat to be used in its evaporation and thus cools the surface of the body  **Characteristics of biochemical reactions** Chemical reactions occurring in vivo have the following properties: **Speed** glucose, for instance, is oxidized in the body with surprising speed, while in vitro, the same reaction is quite a long and tedious process. this is due to the presence of enzymes, without which life as we know it would not be possible **Mildness** energy is taken up and released in a gentle way, not violently as those occurring in vitro (because of high specific heat of water which makes up a large proportion of the protoplasm) **Orderliness** a high degree of orderliness is due to the existence of cell specialization within the different organs of the body **LESSON 2: CARBOHYDRATES** **OCCURENCE AND FUNCTION OF CARBOHYDRATES** **Carbohydrates** - The most abundant class of **bioorganic molecules** on earth - produced by the photosynthetic activity of the green plants - also referred to as **saccharides** because of the sweet taste of many carbohydrates - (Latin, **saccharum**, meaning sugar) - storehouse of chemical energy (glucose, starch, glycogen) - a gram of digested carbohydrate gives about **4 kcal** of energy - complex carbohydrates are best for diet supportive structural components in plants and some animals (cellulose, chitin) - form part of the structural framework of DNA & RNA - carbohydrate \"markers\" on cell surfaces play key roles in cell-cell recognition processes. **CLASSIFICATION OF CARBOHYDRATES** **SIMLR FORMULA:** CnH2nOn or Cn(H2O)n hydrate C where n=bumber of atoms **polyhydroxy** **aldehydes** or **polyhydroxy ketonesn** or compounds that produce such substances upon hydrolysis. **Classification based on products of acid hydrolysis:** **Monosaccharides** - the simple sugars - contain a single polyhydroxy aldehyde or polyhydroxy ketone unit - cannot be degraded into simpler products by hydrolysis reactions pure monosaccharides are water- soluble, white, crystalline solids **Disaccharides** - contains 2 monosaccharide units covalently bonded to each other - crystalline and water soluble substances - upon hydrolysis they produce monosaccharides **Oligosaccharides** - contains 2-10 monosaccharide units - covalently bonded - disaccharides are the most common type - **trisaccharides** (raffinose) - **tetrasaccharides** (stachyose) - free oligosaccharides, other than disaccharides, are less common in nature - usually found associated with proteins and lipids in complex molecules that serve structural and regulatory functions **Polysaccharides** consist of tens of thousands of monosaccharide units covalently bonded homopolysacchrides - polymers of a single monosaccharide (glycogen, cellulose, starch) heteropolysaccharides - contain more than one kind of monosaccharide (hyaluronic acid, heparin, chondroitin sulfate) **STARCH** There are 2 types of starch molecules: -**AMYLOSE** = Long linear chains of glucoseesf -**AMYLOPECTIN** = Long linear and branched chains of glucoses. Each starch can contain 100 to 20,000 molecules of glucose. **GLYCOGEN** -The glycogen structure is composed by long **linear** and **branched** chains of glucoses. -The glycogen is a sugar coming from **animals** (meats) **CELLULOSE** - The cellulose is also composed by long linear chains of glucoses but the glucoses are linked by a different type of chemical bond. **Classification of Monosaccharides** - carbohydrates that have the general formula CnH2nOn n varies from 3-8. - grouped together according to the number of carbons they contain **may either be:** **an aldose** - contains aldehyde group a **ketose** - contains ketone group **General formula** -presence of a ketone group is usually indicated by USING the ending\"\_\_\_\_\_\_\_\_\_\_\_ulose\" in naming the sugar.e.g., levulose **Fischer Projection Formulas** A striking feature of carbohydrate structure is the presence of chirality centers. All carbohydrates except for dihydroxyacetone contain one or more chirality centers. The simplest Aldose, glyceraldehyde, has one chirality center---one carbon atom bonded to four different groups. Thus, there are two possible enantiomers---mirror images that are not superimposable. Only one enantiomer of glyceraldehyde occurs in nature.When the carbon chain is drawn vertically with the aldehyde at the top, the naturally occurring enantiomer has the OH group drawn on the right side of the carbon chain. To distinguish the two enantiomers, the prefixes d and l precede the name. Thus, the naturally occurring enantiomer is labeled d-glyceraldehyde, while the unnatural isomer is l-glyceraldehyde. **Fischer projection formulas** are commonly used to depict the chirality centers in monosaccharides. A Fischer projection formula uses a cross to represent a tetrahedral carbon in which the horizontal bonds come forward (on wedges) and vertical bonds go behind (on dashes). In a Fischer projection formula: **Monosaccharides With More Than One Chirality Center** Fischer projection formulas are also used for compounds like aldohexoses that contain several chirality centers. Glucose, for example, contains four chirality centers labeled in the structure below. To convert the molecule to a Fischer projection, the molecule is drawn with a vertical carbon skeleton with the aldehyde at the top, and the horizontal bonds are assumed to come forward (on wedges). In the Fischer projection, each chirality center is replaced by a cross  - The letters d and l are used to label all monosaccharides, even those with many chirality centers. - The configuration of the chirality center farthest from the carbonyl group determines whether a monosaccharide is d or l. **Glucose and all other naturally occurring sugars are d sugars.** l-Glucose, a compound that does not occur in nature, is the enantiomer of d-glucose. l-Glucose has the opposite configuration at **every** chirality center. **Chirality** A **chiral center** is an atom in a molecule that has four different groups bonded to it in a tetrahedral orientation. A molecule that contains a chiral center is said to be **chiral**. A chiral molecule is a molecule whose mirror images are not superimposable. An **achiral molecule** is a molecule whose mirror images are superimposable The simplest example of a chiral organic molecule, that is a trisubstituted methane molecule such as bromochloroiodomethane. The four different groups bonded to a chiral center need not be just single atoms as was the case in the previous example. In the following chiral-center-containingmolecule, glyceraldehyde, three of the four bonded groups are polyatomic entities. The four different groups attached to the carbon atom at the chiral center in this molecule are -H, -OH, -CHO, and -CH2OH. Isopropyl alcohol (2-propanol) is not a chiral molecule. There are at least two identical groups attached to each of the three carbon atoms present, as is shown in the following analysis: **Chiral centers** within molecules are often denoted by a small asterisk. Note the chiral centers in the following molecules. Indicate whether the circled carbon atom in each of the following molecules is a chiral center. Analysis This is a chiral center. The four different groups attached to the carbon atom are -CH3, -Cl, -CH2-CH3, and H-. **Common Monosaccharides** The most common monosaccharides in nature are the aldohexoses d-glucose and d-galactose, and the ketohexose d-fructose. **Glucose** - also called dextrose, is the sugar referred to when blood sugar is measured. It is the most abundant monosaccharide. - Glucose is the building block for the polysaccharides starch and cellulose. - Glucose, the carbohydrate that is transported in the bloodstream, provides energy for cells when it is metabolized. - Normal blood glucose levels are in the range of 70--110 mg/dL. Excess glucose is converted to the polysaccharide glycogen or fat. - Excess glucose is converted to the polysaccharide glycogen or fat. **Insulin** - a protein produced in the pancreas, regulates blood glucose levels. - When glucose concentration increases after eating, insulin stimulates the uptake of glucose in tissues and it\'s conversion to glycogen. - Patients with diabetes produce insufficient insulin to adequately regulate blood glucose levels, and the concentration of glucose rises. - With close attention to diet and daily insulin injections or other medications, a normal level of glucose can be maintained in most diabetic patients. - Individuals with poorly controlled diabetes can develop many other significant complications, including cardiovascular disease, chronic renal failure, and blindness. **Galactose** - is one of the two monosaccharides that form the disaccharide lactose. - Galactose is a stereoisomer of glucose, since the position of a hydrogen atom and hydroxyl group at a single chirality center are different in the two monosaccharides. - Individuals with galactosemia, a rare inherited disease, lack an enzyme needed to metabolize galactose. - Galactose accumulates, causing a variety of physical problems, including cataracts, cirrhosis, and mental retardation. - Galactosemia can be detected in newborn screening, and affected infants must be given soy-based formula to avoid all milk products with lactose. - When diagnosed early, individuals who eliminate all lactose- and galactose-containing foods can lead a normal life. **Fructose** - is one of two monosaccharides that form the disaccharide sucrose. - Fructose is a ketohexose found in honey and is almost twice as sweet as normal table sugar with about the same number of calories per gram. **The Cyclic Forms Of Monosaccharides** We learned that an aldehyde or ketone reacts with one equivalent of an alcohol to form a hemiacetal, a compound that contains a hydroxyl group (OH) and an alkoxy group (OR) on the same carbon.  Generally, hemiacetals from acyclic reactants are unstable. When a compound contains both a hydroxyl group and an aldehyde or ketone, however, an intramolecular cyclization reaction forms a stable cyclic hemiacetal. The carbon atom that is part of the hemiacetal is a new chirality center, called the **anomeric carbon.** Thus, two different products called **anomers** are formed Image The hydroxyl and carbonyl groups of monosaccharides undergo intramolecular cyclization to form hemiacetals. Let's illustrate the process with d-glucose, and then learn a general method for drawing the cyclic forms of any aldohexose. Which of the five OH groups in glucose is at the right distance from the carbonyl group to form a sixmembered ring? The O atom on the chirality center farthest from the **carbonyl** (C5) is six atoms from the carbonyl carbon, placing it at the proper distance for cyclization to form a six-membered ring with a hemiacetal. To convert this acyclic form (labeled A) into a cyclic hemiacetal, first rotate the carbon skeleton clockwise 90° to form B. Note that groups that were drawn on the right side of the carbon skeleton in A end up below the carbon chain in B. Then twist the chain to put the OH group on C5 close to the aldehyde carbonyl, forming C. In this process, the CH2OH group at the end of the chain ends up above the carbon skeleton. Realize that A, B, and C are all different representations of d-glucose. The molecule has been rotated and twisted but the carbon skeleton and relative arrangement of the substituents have not changed. We are now set to draw the cyclic hemiacetals formed by reaction of the OH group on C5 with the aldehyde carbonyl. Since cyclization creates a new chirality center, **there are two cyclic forms of dglucose**, an 𝛂 **anomer** and a 𝛃 **anomer**. These flat, six-membered rings used to represent the cyclic hemiacetals of glucose and other sugars are called Haworth projections. Thus, d-glucose really exists in three different forms---an acyclic aldehyde and two cyclic hemiacetals---all of which are in equilibrium. Each cyclic hemiacetal can be isolated and crystallized separately, but when any one compound is placed in solution, an equilibrium mixture of all three forms results. This process is called **mutarotation**. At equilibrium, the mixture has 37% of the α anomers, 63% of the β anomer, and only a trace amount of the acyclic aldehyde. Although Haworth projections represent the six-membered ring of glucose as a flat hexagon, in reality, the ring is puckered as shown in the three-dimensional models **Haworth Projections** All aldohexoses exist primarily as cyclic hemiacetals typically drawn in Haworth projections. To convert an acyclic monosaccharide to a Haworth projection, follow the stepwise How To procedure. **HOW TO: Draw A Haworth Projection From An Acyclic Aldohexose** EXAMPLE: Draw both anomers of D-mannose in a Haworth projection **Step \[1\]** Place the O atom in the upper right corner of a hexagon, and add the CH2OH group on the first carbon to the left of the O atom. For naturally occurring D sugars, the CH2OH group is drawn up, above the plane of the six-membered ring. **Step \[2\]** Place the anomeric carbon on the fi rst carbon clockwise from the O atom. For an 𝛂 anomer, the OH is drawn down in a D sugar. For a 𝛃 anomer, the OH is drawn up in a D sugar. **Step \[3\]** Add the substituents (OH and H) to the three remaining carbons (C2--C4), clockwise around the ring. The substituents on the right side of the carbon skeleton (shown in red) are drawn down in the Haworth projection. The substituents on the left side of the carbon skeleton (shown in blue) are drawn up in the Haworth projection. **The Cyclic Forms Of Fructose, A Ketohexose** Certain monosaccharides---notably aldopentoses and ketohexose---form five-membered rings, not six-membered rings, in solution. The same principles apply to drawing these structures as for drawing six-membered rings, except the ring size is one atom smaller. For example, d-fructose forms a five-membered ring when it cyclizes to a hemiacetal because the carbonyl group is a ketone at C2, instead of an aldehyde at C1. Note that the cyclic structures of fructose contain two CH2OH groups bonded to the five-membered ring, one of which is located at the anomeric carbon. **Disaccharides** Disaccharides are carbohydrates composed of two monosaccharides. Disaccharides are acetals, compounds that contain two alkoxy groups (OR groups) bonded to the same carbon. In a similar fashion, a disaccharide results when a hemiacetal of one monosaccharide reacts with a hydroxyl group of a second monosaccharide to form an acetal. The new C O bond that joins the two rings together is called a **glycosidic linkage.** The two monosaccharide rings may be five-membered or sixmembered. All disaccharides contain at least one acetal that joins the rings together. Each ring is numbered beginning at the anomeric carbon, the carbon in each ring bonded to two oxygen atoms. The glycosidic linkage that joins the two monosaccharides in a disaccharide can be oriented in two different ways, shown with Haworth projections in structures A and B. Numbers are used to designate which ring atoms are joined in the disaccharide. Disaccharide A has a **1→4-𝛂-glycosidic** linkage since the glycoside bond is oriented down and joins C1 of one ring to C4 of the other. Disaccharide B has a **1→4-𝛃-glycosidic** linkage since the glycoside bond is oriented up and joins C1 of one ring to C4 of the other. **FOCUS ON HEALTH & MEDICINE** **Lactose Intolerance** **Lactose** is the principal disaccharide found in milk from both humans and cows. Unlike many mono- and disaccharides, lactose is not appreciably sweet. Lactose consists of one galactose ring and one glucose ring, joined by a 1→4-β-glycoside bond from the anomeric carbon of galactose to C4 of glucose. **Lactose** is digested in the body by first cleaving the 1→4-β- glycoside bond using the enzyme lactase. Individuals who are lactose intolerant no longer produce this enzyme, and so lactose cannot be properly digested, causing abdominal cramps and diarrhea. Lactose intolerance is especially prevalent **Sucrose And Artificial Sweeteners** **Sucrose**, the disaccharide found in sugarcane and the compound generally referred to as "sugar," is the most common disaccharide in nature. It contains one glucose ring and one fructose ring. Unlike maltose and lactose, which contain only six-membered rings, sucrose contains one six membered and one five-membered ring. **Sucrose's** pleasant sweetness has made it a widely used ingredient in baked goods, cereals, bread, and many other products. It is estimated that the average American ingests 100 lb of sucrose annually. Like other carbohydrates, however, sucrose contains many calories. To reduce caloric intake while maintaining sweetness, a variety of artifi cial sweeteners have been developed. These include aspartame, saccharin, and sucralose. These compounds are much sweeter than sucrose, so only a small amount of each compound is needed to achieve the same level of perceived sweetness. A relative sweetness scale ranks the sweetness of carbohydrates and synthetic sweeteners, **Aspartame** (trade name: Nutrasweet) is used in the artificial sweetener Equal and many diet beverages. While harmless to most individuals, aspartame is hydrolyzed in the body to the amino acid phenylalanine (and other products). Infants afflicted with phenylketonuria cannot metabolize this amino acid, so it accumulates, causing mental retardation. When this condition is identified early, a diet limiting the consumption of phenylalanine (and compounds like aspartame that are converted to it) can make a normal life possible. **Polysaccharides** **Polysaccharides** contain three or more monosaccharides joined together. Three prevalent polysaccharides in nature are **cellulose, starch, and glycogen,** each of which consists of repeating glucose units joined by glycosidic bonds. **Cellulose** **Cellulose** is found in the cell walls of nearly all plants, where it gives support and rigidity to wood, plant stems, and grass. Wood, cotton, and flax are composed largely of cellulose. **Cellulose is an unbranched polymer composed of repeating glucose units joined in a 1→4-𝛃- glycosidic linkage.** The β glycosidic linkages create long linear chains of cellulose molecules that stack in sheets, making an extensive three-dimensional array.  **Cellulose** In some cells, cellulose is hydrolyzed by an enzyme called a 𝛃-glycosidase, which cleaves all of the β glycoside bonds, forming glucose. Humans do not possess this enzyme, and therefore cannot digest cellulose. Ruminant animals, on the other hand, such as cattle, deer, and camels, have bacteria containing this enzyme in their digestive systems, so they can derive nutritional benefit from eating grass and leaves. Much of the insoluble fiber in our diet is cellulose, which passes through the digestive System without being metabolized. Foods rich in cellulose include whole wheat bread, brown rice, and bran cereals. Fiber is an important component of the diet even though it gives us no nutrition fiber adds bulk to solid waste, so that it is eliminated more readily. **Useful Carbohydrate Derivatives** Many other simple and complex carbohydrates with useful properties exist in the biological world. Several are derived from monosaccharides that contain an amino (NH2) or amide (NHCOCH3) group in place of an OH group. Examples include d-glucosamine, the most abundant amino sugar in nature, and N-acetyl-dglucosamine (NAG). Other carbohydrates are derived from dglucuronate, which contains a carboxylate anion, COO--, in place of the CH2OH group of the typical monosaccharide skeleton. **Glycosaminoglycans** Glycosaminoglycans (GAGs) are a group of unbranched carbohydrates derived from alternating amino sugar and glucuronate units. Glycosaminoglycans form a gel-like matrix that acts as a lubricant, making them key components in Connective tissue and joints. Examples include hyaluronate, which is found in the extracellular Fluid that lubricates joints and the vitreous humor of the eye; chondroitin, a component of cartilage and tendons; and heparin, which is stored in the mast cells of the liver and other organs and prevents blood clotting. While the monosaccharide rings of hyaluronate and chondroitin are joined by β glycosidic linkages (shown in blue), those of heparin are joined by α glycosidic linkages (shown in red). **Chitin** **Chitin**, the second most abundant carbohydrate polymer, is a polysaccharide formed from N-acetyl-d-glucosamine units joined together in **1→4-𝛃-glycosidic** linkages. Chitin is identical in structure to cellulose, except that each OH group at C2 is now replaced by NHCOCH3. The exoskeletons of lobsters, crabs, and shrimp are composed of chitin. Like cellulose, chitin chains are held together by an extensive network of hydrogen bonds, forming water-insoluble sheets. **Blood Type** **Human blood** is classified into one of four types using the ABO system discovered in the early 1900s by Karl Landsteiner. There are four blood types---A, B, AB, and O. An individual's blood type is determined by three or four monosaccharides attached to a membrane protein of red blood cells. These monosaccharides include: Each blood type is associated with a different carbohydrate structure, Three monosaccharides occur in all blood types---Nacetyl-d-glucosamine, d-galactose, and l-fucose. Type A blood contains a fourth monosaccharide, N-acetyl-d-galactosamine, and type B blood contains an additional d-galactose unit. Type AB blood has both type A and type B carbohydrates. The short polysaccharide chains distinguish one type of red blood cell from another, and signal the cells about foreign viruses, bacteria, and other agents. When a foreign substance enters the blood, the body's immune system uses antibodies to attack and destroy the invading substance so that it does the host organism no harm. Knowing an individual's blood type is necessary before receiving a blood transfusion. Because the blood of an individual may contain antibodies to another blood type, the types of blood that can be given to a patient are often limited. An individual with blood type A produces antibodies to type B blood, and an individual with blood type B produces antibodies to type A blood. Type AB blood contains no antibodies to other blood types, while type O blood contains antibodies to both types A and B. As a result: