Carbohydrates and Connective Tissues PDF

Carbohydrates and connective tissues Presented by: Dr Alshaymaa Darwish  Definition of carbohydrates  CHO may be defined chemically as aldehyde or ketone derivatives of polyhydroxy alcohols or as compounds that yield these derivatives on hydrolysis.  Chemically, they contai...

Carbohydrates and connective tissues Presented by: Dr Alshaymaa Darwish  Definition of carbohydrates  CHO may be defined chemically as aldehyde or ketone derivatives of polyhydroxy alcohols or as compounds that yield these derivatives on hydrolysis.  Chemically, they contain the elements carbon, hydrogen and oxygen. The empirical formula of many simple carbohydrates is [CH2O]n. Hence, the name “carbohydrate”, i.e. hydrated carbon. They are also called “saccharides”. In Greek, saccharon means sugar.  Some carbohydrates also contain nitrogen, phosphorus or sulfur.  Function of carbohydrates CHO)  Source of energy for living beings, e.g. glucose (provide energy)  Storage form of energy, e.g. glycogen in animal tissue and starch in plants  Serve as structural component(polymeric CHO), e.g. glycosaminoglycans in humans, cellulose in plants and chitin in insects (structural)  Non-digestable carbohydrates like cellulose, serve as dietary fibers  Constituent of nucleic acids RNA and DNA, e.g. ribose and deoxyribose sugar  Play a role in lubrication, cellular intercommunication and immunity (mucopolysaccharides)  Carbohydrates are also involved in detoxification, e.g. glucuronic acid.  Glycoprotein and glycolipid are component of cell membrane receptors  Excessive CHO in body can converted to fats (storage)  Classification of carbohydrates Conjugated CHO Simple CHO complex CHO Saccharides - Glycolipid - Proteoglycan - Glycoprotein  Monosaccharides According to No of carbons  Mono= One According to Functional group  Include carbohydrates that are soluble in water and sweet to taste.  They consist of a single polyhydroxy aldehyde or ketone unit, and thus cannot be hydrolyzed into a simpler form.  The most abundant monosaccharide in nature is six carbon sugar-D-glucose.  Biological importance of Monosaccharides  Monosaccharide  Physiologically and biomedically, glucose is the most important monosaccharide.  In solution, CHO (C1)or C=O (C2) group of monosaccharide react with a hydroxy (OH)in (C-5 or C4) in the same molecule forming a bond hemiacetal or hemiketal respectively.  That form either six membered ring called glucopyranose or five membered ring called glucofuranose, respectively.  In case of glucose, the six membered glucopyranose is much more stable While In the case of fructose, the more stable form is fructofuranose.  Other than anomeric carbon Maturation Racemic mixture  ISOMERISM  Greek ‘isos’ means equal, ‘meros’ means parts. The compounds possessing identical molecular formula but different structures are referred to as isomers. 1. Ketose-aldose isomerism (constitutional isomers) (glucose& fructose) 2. D and L isomerism: depends on the orientation of the H and OH groups around the asymmetric carbon atom adjacent to the terminal primary alcohol Carbon. NB: D and L isomers are mirror images of each other. These two forms are called enantiomers.  ISOMERISM 3. Optical isomerism:When equal amount of D and L isomers are present, the resulting mixture has no optical activity. Since the activity of each isomer cancel one another, such a mixture is said to be a racemic or dl mixture. 4. Epimerism:When two monosaccharides differ from each other in their configuration around a single asymmetric carbon (other than anomeric carbon) atom, they are referred to as epimers of each other.  ISOMERISM 5. Anomeric (α and β Anomerism): - An additional asymmetric center is created when glucose cyclizes. - Carbon-1(anomeric C) of glucose in the open chain form, becomes an asymmetric carbon in the ring form. - The designation α means that the hydroxyl group attached to C-1 is below the plane of the ring, - β means that it is above the plane of the ring.  Maturation  Mutarotation is defined as the change in the specific optical rotation by the interconversion of α and β- forms of D-glucose to an equilibrium mixture.  the formation of an equilibrium mixture containing about one-third α-anomers and two-thirds β- anomers.  Phosphoric acid ester of monosaccharides: Phosphorylation of glucose to prevent the diffusion of the sugar out of the cell e.g glucose-6-phosphate. Amino sugar: hydroxyl group replaced by an amino or an Some important acetylated amino (acetylamino) group e.g. glucosamine, N- acetyl glucosamine they enter in glycolipid, glycoprotein and sugar derivatives of proteoglycan. monosaccharides Deoxy sugars: hydrogen atom in place of one of their hydroxy groups e.g. 2-deoxyribose found in DNA. are: Sugar acids: oxidation of the monosaccharides e.g. Glucuronic acid act as conjugated agent and L-iduronic epimer of glucuronic acid. Sugar alcohols: product of monosaccharide-reduction acid e.g sorbitol from glucose reduction. Neuraminic: (9C) Manosamine + Pyruvate ————> Neuraminic acid Sialic acid: N-Acetylated derivatives of neuraminic constituents of both glycoproteins and glycolipids (ganglioside).  Disaccharide  Disaccharides consist of two monosaccharide units bind by glycosidic bond.  Glycosides are formed when the hydroxyl group of anomeric carbon of a monosaccharide reacts with OH or NH group of second compound that may or may not be a carbohydrate  They are crystalline, water soluble and sweet to taste Glucose+ galactose Glucose+ glucose Glucose+ glucose Glucose+ fructose Glucose+ glucose Disaccharide  Polysaccharide (Glycans) - composed of ten or more monosaccharide units or their derivatives - In polysaccharides, monosaccharide units are joined together by glycosidic linkages. Polysaccharides are subclassified in two groups. 1. Homopolysaccharides (Homoglycans): 2. Heteropolysaccharides (Heteroglycans): Glycosaminoglyc ans (GAGs) Polysaccharides Amylopectin Amylose α(1-4) α(1-4) Α(1-6)  Cell wall Homoglycan s   A GAG is an unbranched heteropolysaccharide, made up of Heteropolysac repeating disaccharides.  – One component of which is always an amino sugar (hence the charides or name glycosaminoglycans), either D-glucosamine or D- galactosamine. Heteroglycans  – The other component of the repeating disaccharide is a uronic 2. acid, either L-glucuronic acid or its epimer L-iduronic acid.  Thus, GAG is a polymer of [uronic acid-amino sugar]n Glycosaminog  This polymer is attached covalently to extracellular proteins called core protein (except hyaluronic acid) to form lycans (GAGs) proteoglycans. A resulting structure resembles a “bottle brush”  The proteoglycan monomer associates with a molecule of or hyaluronic acid to form proteoglycan. Mucopolysacc harides Connective tissues  Connective tissue serves a connecting function. It give strength, support and binds other tissues.  It has cells scattered throughout an extracellular matrix. It is a system of insoluble protein fibers embedded in a matrix called the ground substance.  Connective tissue is widely distributed in the body, the tendons, ligaments, cartilage and matrix of bone.  BASIC COMPONENTS OF CONNECTIVE TISSUE  BASIC COMPONENTS OF CONNECTIVE TISSUE (1- collagen 19)  The basic structural unit of collagen is tropocollagen, which consists of three equal length polypeptide chains called α-chains (1ry structure).  α-chains composed of 33% of the total residues being glycine (Gly), 10% proline (Pro), 10% hydroxyproline (Hyp) and 1% hydroxylysine (Hyl).  Glycine (every third position) is the smallest AA enough to be accommodated in the limited space available in the central core of the helix.  The three polypeptide chains are held together by hydrogen bonds between chains (intrachain) (2ry structure).  These three polypeptide chains twisted around each other in a triple helix forming a rope like structure, which has great tensile strength.  BASIC COMPONENTS OF CONNECTIVE TISSUE (2- elastin)  Elastin is a rubber-like protein, which can stretch to several times their length and then rapidly return to their original size and shape when the tension is released.  In contrast to collagen (19 types), there is only one genetic type of elastin.  The basic subunit of elastin fibrils is tropoelastin which contains about 800 amino acid residues.  Although elastin and collagen contain similarly high amounts of glycine and proline, elastin contains less hydroxyproline and no hydroxylysine.  Elastin has very high content of alanine and other nonpolar aliphatic residue, i.e. valine, leucine and isoleucine.  The major cross-links formed in elastin are the desmosines, permit the elastin to stretch in two dimensions and subsequently recoil during the performance of its physiologic functions  BASIC COMPONENTS OF CONNECTIVE TISSUE (3- Proteoglycans)  Intracellular ground substance of connective tissue contains proteoglycans and glycoproteins in which fibrous elements of connective tissues are embedded.  They connect cell and other connective elements in the extracellular matrix.  Proteoglycan is a complex formed by polysaccharide called glycosaminoglycans (about 95%) and protein (about 5%).  Hyaluronic acid, chondroitin sulfate, keratan sulfate, heparan sulfate and heparin are the major glycosaminoglycans.  BASIC COMPONENTS OF CONNECTIVE TISSUE (4- Glycoproteins)  Glycoproteins are proteins to which oligosaccharides are covalently attached.  The main function of glycoprotein is to facilitate adhesion between various elements of connective tissue.  Some glycoproteins present in connective tissue are: – Fibrillin – Fibronectin – Lamin – Tenascin.