carbohydrates(1)

Chapter 2 Lecture: Carbohydrates

• Instructor: Christina A. Johnson, Ph.D., University of California, San Diego

• Source: Fundamentals of General, Organic, and Biological Chemistry, 8th Edition, Pearson Education, Inc.

20.1 An Introduction to Carbohydrates

• Learning Objective: Classify carbohydrates by functional group and number of carbon atoms.

• Definition: Carbohydrates are polyhydroxy aldehydes and ketones.

Classification of Carbohydrates

• Monosaccharides (Simple Sugars):

  • Consist of 3 to 7 carbon atoms.

  • Contain one aldehyde (aldose) or one ketone group (ketose).

• Functional Group Placement:

  • Aldehyde group at the end of the carbon chain.

  • Ketone group on the second carbon of the chain.

Naming Carbohydrates

• Suffix -ose indicates a carbohydrate.

• Common names: glucose, ribose, fructose.

• Prefixes for carbon number: tri-, tetr-, pent-, hex-, hept-.

Structures of Common Monosaccharides

• Glucose (Aldohexose): Energy source, monomer for starch and cellulose.

• Ribose (Aldopentose): Component of ATP, coenzymes, and RNA.

• Fructose (Ketohexose): Found in fruits, component of sucrose.

20.2 Handedness of Carbohydrates and Fischer Projections

• Learning Objectives: Identify D and L enantiomers and draw Fischer projections.

• Chirality: Chiral compounds lack symmetry, existing as D (right-handed) and L (left-handed) forms.

• Fischer Projections:

  • Represent chiral centers; horizontal lines project out and vertical lines behind the page.

D and L Classification

• D sugars: Hydroxyl group (-OH) on the chiral carbon furthest from the carbonyl points right.

• L sugars: Hydroxyl group on the chiral carbon points left.

20.3 Structure of Glucose and Other Monosaccharides

• Learning Objectives: Convert Fischer projection to Haworth projection, identify anomeric carbon and forms.

• D-Glucose: Most abundant monosaccharide; exists as open-chain aldehyde or cyclic hemiacetals.

• Cyclic Forms: Differ at C1; anomers defined by the orientation of the -OH group.

• Mutarotation: Equilibrium established between open-chain and cyclic forms of glucose.

Monosaccharide Structures - Summary

• Monosaccharides: polyhydroxy aldehydes/ketones, typically 3-7 carbons.

• D and L forms depend on the orientation of the -OH group relative to carbonyl carbon.

20.4 Some Important Monosaccharides

• Learning Objective: Identify common monosaccharides, their sources, and functions.

• Monosaccharides are sweet-tasting and generally soluble in water.

• Common examples:

  • D-Glucose: Blood sugar, source of metabolic energy, stored as glycogen.

  • D-Galactose: Component of lactose, metabolized to glucose, has implications for galactosemia.

  • D-Fructose: Found in fruits and honey, sweeter than glucose, used in food production.

  • Ribose and 2-Deoxyribose: Components of RNA and DNA, plays roles in genetic material and metabolism.

20.5 Reactions of Monosaccharides

• Learning Objectives: Predict products of oxidation, reduction, glycoside, and phosphorylation reactions.

• Monosaccharides undergo various chemical reactions:

  • Oxidation-Reduction: Aldehydes oxidized to carboxylic acids, ketones can also act as reducing sugars.

  • Glycosidic Bond Formation: React with alcohols to form glycosides.

  • Phosphate Esters: Important in metabolism, formed by the reaction of monosaccharides with phosphate groups.

20.6 Common Disaccharides

• Learning Objective: Identify common disaccharides, their subunits, and functions.

• Disaccharides are composed of two monosaccharides linked by glycosidic bonds.

• Types of common disaccharides include:

  • Maltose: Reducing sugar, generated during starch digestion.

  • Lactose: Milk sugar, hydrolyzed by lactase – lactose intolerance implications.

  • Sucrose: Table sugar, not a reducing sugar, hydrolyzed into glucose and fructose.

20.7 Some Important Polysaccharides Based on Glucose

• Learning Objectives: Recognize common polysaccharides, their functions, and structures.

• Polysaccharides are polymers of monosaccharides, containing glucose:

  • Cellulose: Most abundant polysaccharide, provides structure in plant cell walls, indigestible by humans.

  • Amylose: Starch component, soluble in water, energy source.

  • Amylopectin: Branched starch form, used for energy storage, insoluble in hot water, highly branched.

  • Glycogen: Animal version of starch, highly branched for rapid energy release during exercise.

Modified Monosaccharides in Polysaccharides

• Hyaluronate: Found in joints;

• Chondroiton-6-sulfate: Component of cartilage;

• Heparin: Anticoagulant function.

Concept Map

• Carbohydrates: Organic molecules classified into monosaccharides, disaccharides, and polysaccharides based on carbon chain length.

• Structure and Function: Monosaccharides provide energy and build larger structures, while polysaccharides serve various roles in storage and structural integrity.