Biochemistry 1 Lecture 2 PDF

Biochemistry 1 First level Lecture 2 Carbohydrate Overview ❖Defenition of carbohydrate ❖Function of carbohydrate ❖Classification of carbohydrates ❖Monosaccharides ❖Disaccharides ❖polysaccharide  Introduction Carbohydrates are organic compounds that containing...

Biochemistry 1 First level Lecture 2 Carbohydrate Overview ❖Defenition of carbohydrate ❖Function of carbohydrate ❖Classification of carbohydrates ❖Monosaccharides ❖Disaccharides ❖polysaccharide  Introduction Carbohydrates are organic compounds that containing C, H & O “Carbon-Hydrate”. They are polyhydroxy aldehydes or polyhydroxy ketones or compounds yielding them on hydrolysis. General formula of Monosaccharides: Cn(H2O)n or CnH2nOn “carbon hydrates or Hydrates of Carbon” C6H12O6= C6(H2O)6  Function & Importance of Carbohydrates 1. Major source of energy, as they provide the body with about 50% of it’s energy. 2. Mucopolysaccharides, proteoglycans & glycoproteins (structural carbohydrates) are important component of cell membranes & connective tissues. 3. Phosphorylated Pentoses e.g. Ribose-5-phosphate & deoxy ribose-5-phosphate, inter in the structures of nucleosides, nucleotides & nucleic acids (RNA & DNA). 4. Non-digestible carbohydrate, Cellulose gives the bulk of stools, increases intestinal movement (peristalsis), so preventing constipation. 5. Heparin is an important natural anticoagulant  Classification of carbohydrate 1. Monosaccharides (Simple sugar): They can not give simpler form on hydrolysis. 2. Oligosaccharides: Sugars composed of few (2 – 10) monosaccharide residues. Two to ten monosaccharides covalently linked. 1. Polysaccharides: Polymers of more than 10 monosaccharide residues. polymers consisting of chains of monosaccharide or disaccharide units.  Monosaccharides (CnH2nOn) Firstly: Classified according the number of carbon atoms into: Triose 3 Carbons Hexose 6 Carbons Tetrose 4 Carbons Heptoses 7 Carbons Pentose 5 Carbons Secondly: Whether they are aldehydes (Aldoses) or ketones (Ketoses). A- Trioses (3 carbon atoms, C3H6O3) CH2-OH C=O CH2-OH Dihydroxyacetone  Systems for numbering the carbon atoms The carbons are numbered 1 1 CHO CH2OH 2 starting from aldehyde group as H C OH 2 C=O 3 3 carbon number 1. HO C H HO C H 4 4 In case of ketoses, the carbon H C OH H C OH 5 5 H C OH H C OH of ketone group is the carbon 6 CH2OH 6 CH2OH number 2.  Cyclic structure of monosaccharide Less than 1% of each of the monosaccharides with five or more carbons exists in the open chain (acyclic) form. There are predominantly found in a ring (cyclic) form, in which the aldehyde (or keto) group has reacted with an alcohol group on the same sugar, making the carbonyl carbon asymmetric.  Properties of monosaccharides A- Physical properties: 1- All monosaccharides are soluble in water. 2- All monosaccharides show the property of optical activity. 3- All monosaccharides can exist in α and β forms.  Sugar Derivatives 1. Sugar Alcohol: by reduction to sugar alcohols (Alditols) Glyceraldehyde → Glycerol Ribose → Ribitol (In Riboflavin) Mannose → Mannitol Fructose → Sorbitol Glucose → Inositol, Sorbitol 2. Sugar Acids:These are produced by oxidation of carbonyl carbon, last hydroxyl carbon or both. 1- Aldonic acids (mild oxidation): Oxidation of carbonyl carbon to carboxylic group gives aldonic acid. Glyceraldehyde → Glyceric acid Glucose → Gluconic acid Galactose → Galactonic acid 2-Uronic acids (moderate oxidation): Oxidation of last hydroxyl carbon will give uronic acid Glucose → Glucuronic acid Galactose → Galacturonic acid 3-Aldaric acids (strong oxidation): These are di- carboxylic acids produced by oxidation of both carbonyl group and last hydroxyl group into carboxylic group e.g. glucose will be oxidized to glucaric acid (saccharic acid) Glucose → Glucaric acid (Saccharic acid) Galactose → Galactaric acid (Mucic acid)  3. Deoxy sugars Are sugars in which one of the hydroxyl groups has been replaced by a hydrogen atom i.e. one oxygen is missed. Examples: 1- Deoxyribose which occurs in nucleic acid DNA.  4. Amino sugars (Sugaramines) In these sugars, the hydroxyl group is replaced by an amino or an acetylamino group. Amino sugars are constituents of glycoproteins, gangliosides and glucosaminoglycans. Examples: Glucosamine (Chitosamine): found in the shells of insects. Galactosamine (Chondrosamine): found in chondroitin.  Glycosidic bond Glycosidic bond is the bond between a carbohydrate and another compound to form a complex carbohydrate. This bond is between the hydroxyl group of anomeric carbon of monosaccharide (carbon 1 in aldoses and carbon 2 in ketoses) and another compound. α and β glycosidic bond Disaccharides  Disaccharides Two monosaccharides joined by an O-glycosidic bond. Its general formula is Cn(H2O)n-1. Maltose is formed from two -D(+)-glucose molecules. Has an (1→4) glycosidic bond.  Maltose is an intermediate in the hydrolysis of starch. Also known as malt sugar.   − −  Isomaltose Formed from two -D(+)-glucose units. It has an (1→6) bond An intermediate in the hydrolysis of branch point of starch.  Lactose (milk sugar) It is a disaccharide sugar synthesized by galactose and glucose subunits and has the molecular formula C12H22O11. It is the carbohydrate source in the milk.  Sucrose It is the most common sugar in all plant. It is present in sugar cane and beets. It is a disaccharide of α-glucose and β- fructose.  Cellobiose It is like maltose (it is composed of two molecules of D-glucose but the linkage is  Polysaccharide A polysaccharide is a carbohydrate formed by long chains of repeating units linked together by glycosidic bonds.  Types of Polysaccharide Storage polysaccharide: Act as reserve food. Hydrolyzed to sugars required for respiration and biosynthesis. e.g. starch, glycogen, and inulin. Structural polysaccharide: Fibrous. E.g cellulose  Starch Starch is composed of two parts: ❑ Side chain occurs every 24-30 unit. ❑ Hydrolysis of Starch (Acid or Enzymatic): Starch Amylodextrin + Maltose (Traces) Erythrodextrin + Maltose (Traces) Achrodextrin + Maltose Maltose.  Properties: Starch gives a blue color with iodine. Amylopectin gives a red color with iodine. Partial hydrolysis (digestion) by amylase gives various forms of dextrins.  Dextrins Dextrins are partial hydrolytic products of starch. They include Amylodextrins, Erythrodextrins and Achrodextrins. Dextrins are used as Infant feeding and Adhesives and binders in tablet preparations.  Glycogen Energy storage in animals. Stored in liver and muscle as granules. Similar to amylopectin. But glycogen has more (1→6) branches (every 8 – 12 units). Up to 50,000 glucose units. Properties: It gives a red color with iodine.  Cellulose It is the most abundant polysaccharide. β-(1 4) glycosidic linkage. Result in long fiber- for plant structure. Cellulose gives rigidity and strength to cell walls. Cellulose (n = up to 15,000) In partial hydrolysis with acids, cellobiose is produced, while with complete hydrolysis, –glucose is obtained.  Cellulose - Its presence in diet is important, because it cannot be digested, so it will increase the bulk of stool and stimulate the intestinal movement and prevent constipation. - Cellulose can be utilized and serve as a source of energy in herbivores because their gut contain bacterial enzyme that can attack β-linkage. Properties: 1. Cellulose gives no color with iodine. 2. It is insoluble in water. 3. Cellulose in diet cannot be digested by many mammals including humans due to absence of hydrolase enzymes that attacks β-linkage. Inulin it is a polymer of fructose units. It is present in artichokes and used as a diagnostic test for glomerular filteration rate. Properties: Soluble in warm water. Heteropolysaccharide Pectins They are present in the fruits of various plants. They are another example of structural polysaccharide. On hydrolysis they give: galactose, arabinose and galacturonic acid.  Gum Arabic Heteropolysaccharides, contains galactose and glucuronic acid. Agar-agar It is a poly saccharide formed of galactose. It is prepared from sea weeds. The importance of agar agar is due to its use as a culture medium for growing of bacteria in bacteriological studies  Glycoprotein It consists mainly of protein with a small amount of carbohydrates. It is the protein that is covalently bound to carbohydrate units. They have many biological functions: ❖ Immunological protection ❖ Cell-cell recognition ❖ Blood clotting factors ❖ Interaction with other factors ❖ Forming a protective layer on the surface of some cells  Glycosaminoglycans (GAGs) The viscous and lubricating properties of mucous secretions result from the presence of GAGs, so the original naming Mucopolysaccharides. GAGs are long, in most cases un–branched, negatively charged heteropolysaccharide chains associated with a small amount (5%) of protein (carbohydrates 95%). GAGs have the special ability to bind large amounts of water, thereby producing the gel–like matrix that forms the bases of the body’s ground substance.