Carbohydrates
Carbohydrates Composed of the elements C, H, O They are hydrates of carbon Carbon + H2O Empirical formula: CH2O C:H:O ratio is 1:2:1 Contain many hydroxyl groups Contain either an aldehyde or ketone Polar (= hydrophilic)
Types of carbohydrates: Monosaccharide Disaccharides Polysaccharides
Monosaccharide Contain 3 - 7 carbon atoms Empirical formula: (C1H2O1)n if n=3: C3H6O3 if n=5: C5H10O5 if n=6: C6H12O6
Monosaccharides Standard empirical formula (CH2O)n Glucose = C6H12O6 Fructose = C6H12O6 Ribose = C5H10O5 Glyceraldehyde = C3H6O3 Contain hydroxyl & carbonyl groups Can switch between linear / ring Main fuel molecules for cells Over 200 types of monosaccharides Carbon numbers of 5 and 6 are most common
Naming Monosaccharides Most common: 3, 5, 6 Carbons 3 Carbons – Triose 5 Carbons – Pentose 6 Carbons – Hexose The ending -ose denotes a carbohydrate. Simple sugars (monosaccharides) contain one aldehyde or ketone If has a ketone group, it can be called a ketose If has an aldehyde group, it can be called an aldose
Trioses Glyceraldehyde is a triose and an aldose, thus it is a aldotriose. Dihydroxyacetone is a triose and a ketose, thus it is a ketotriose.
Pentoses deoxyribose ribose Ribose and deoxyribose are both pentoses and aldoses, or aldopentoses. Ribose and deoxyribose differ around carbon #2. deoxyribose ribose
Hexoses Glucose is an aldohexose Fructose is a ketohexose
Glucose and fructose are structural isomers They have identical molecular formulas But the atoms arranged differently. Fructose is a ketohexose Glucose is an aldohexose See previous slide
Glucose and galactose are stereoisomers= (enantiomers) Both are aldohexoses. They have identical molecular formulas, But Carbon #4 are mirror images of each other
Enantiomers (= Stereoisomers)
Hexoses In solution a hexose will form a ring. To assume this structure: Carbon 1 forms a covalent bond with the oxygen on carbon 5; The doubled bonded oxygen on carbon 1 accepts a hydrogen atom and is reduced to an alcohol (-OH).
Glucose Ring Formation OH β -glucose OH
α - and β -glucose α -Glucose (alpha): -OH is on the opposite side of the ring as the -CH2OH. β -Glucose (beta): -OH is on the same side of the ring as the -CH2OH. Remember β “balloon up” See previous slide
Disaccharides Two (2) monosaccharide rings joined by a glycoside linkage (a.k.a. glycosidic bond) mono + mono ---> mono--mono + H20 (disaccharide) Look familiar?? Formed by a condensation rxn. Examples of disaccharides maltose, sucrose, lactose
Disaccharides Sucrose
Hydrolysis of Disaccharides Maltose 1. Maltose + H2O -*--> glucose + glucose 2. * = enzyme; in this case maltase 3. Enzymes end in -ase Sucrose 1. Sucrose + H2O -*-> glucose + fructose 2. * = sucrase Hydrolysis of Lactose 1. Lactose + H2O -*-> galactose + glucose 2. * = lactase
Polysaccharides Repeating units of simple sugars (monosaccharides) joined by glycoside linkages. The sugar is usually glucose.
Cellulose Is a homopolymer of glucose. Joined by β -glycoside linkages Is a structural polysaccharide in plant cell walls. What enzyme would digest cellulose? (Cellulase)
Polysaccharide structures Amylose (starch) alpha-glycoside linkages Cellulose beta-glycoside linkages
Plant Starch Is also a homopolymer of glucose. Joined by α -glycoside linkages Is a storage polysaccharide; 2 forms: - amylose (unbranched) - amylopectin (branched) See previous slide for amylose What enzyme would digest amylose? (Amylase)
Amylopectin Structure
Animal starch Glycogen – animal storage polysaccharide Is also a homopolymer of glucose Joined by a-glycoside linkages Same as amylopectin, but more highly branched
Structure of Glycogen
Chitin Is a homopolymer of N-acetyl glycosamine Joined by b-glycoside linkages Is a structural polysaccharide found in fungal cell walls and in the exoskeleton of arthropods.
Chitin
Other Polysaccharides Chondroitin - Major polysaccharide of cartilage. Heparin - Anticoagulant; prevents blood clots. Hyaluronic acid - "glue" between animal cells