Chapter 15

Chapter 15: Carbohydrates

Overview

• Carbohydrates are essential biomolecules that serve as a major source of energy in our diet.

• They are composed of carbon (C), hydrogen (H), and oxygen (O) and are often referred to as saccharides, meaning "sugars."

Role of Carbohydrates in Health

• Diabetes management involves monitoring blood sugar levels and understanding symptoms which may involve nerve damage and vision loss.

• Knowledge of the endocrine system is necessary, especially as it relates to diseases associated with obesity.

15.1 Carbohydrate Classification

• Monosaccharides: Simplest form of carbohydrates (example: glucose).

• Disaccharides: Composed of two monosaccharides (example: sucrose).

• Polysaccharides: Multiple monosaccharides linked together (example: starch, cellulose).

Learning Goals

• Classify monosaccharides as aldoses or ketoses (based on carbonyl groups).

• Determine the number of carbon atoms present in monosaccharides.

15.2 Monosaccharides

• Structure:

  • Contain several hydroxyl (-OH) groups and a chain of 3 to 8 carbon atoms.

  • Classification:

    • Aldoses: Contain an aldehyde group.

    • Ketoses: Contain a ketone group.

• Types of Monosaccharides:

  • Triose: 3 carbon atoms

  • Tetrose: 4 carbon atoms

  • Pentose: 5 carbon atoms

  • Hexose: 6 carbon atoms

15.3 Chiral Molecules

• Chirality: An object is chiral when its mirror image cannot be superimposed onto it; hands are a classic example.

  • Chiral carbon: A carbon atom bonded to four different atoms/groups.

  • Enantiomers: Non-superimposable mirror images of chiral molecules.

15.4 Fischer Projections

• A method to represent carbohydrate structures in 2D.

• Positions of groups relative to chiral carbons affect the D/L notation:

  • D: -OH on the right of the chiral carbon farthest from the carbonyl group.

  • L: -OH on the left.

15.5 Chemical Properties of Monosaccharides

• Reducing Sugars: Monosaccharides that can reduce other compounds, featuring an aldehyde group. Examples include glucose and fructose.

• Sugar Alcohols: Formed from the reduction of monosaccharides, commonly used as sweeteners in sugar-free products.

15.6 Disaccharides

• Formation: Created from two monosaccharides through a dehydration reaction.

  • Examples include maltose (from two glucose molecules), lactose (glucose + galactose), and sucrose (glucose + fructose).

15.7 Polysaccharides

• Polysaccharides are large molecules made from numerous monosaccharide units.

  • Types:

    • Amylose: Unbranched chains (20% of starch).

    • Amylopectin: Branched structure (80% of starch).

    • Glycogen: Animal storage form of glucose (highly branched).

    • Cellulose: Major structural component in plants, not digestible by humans.

Health Connection

• Glycosaminoglycans: Polysaccharides consisting of repeating disaccharide units, play roles in structural integrity and fluid regulation in the body.

• Understanding various carbohydrate structures and their properties is crucial for health applications, particularly in relation to diseases like diabetes.