The Molecules of Life Figures 3.8 – 3.15 CHAPTER 3 The Molecules of Life Figures 3.8 – 3.15

There are four categories of large molecules in cells BIOLOGICAL MOLECULES There are four categories of large molecules in cells Carbohydrates Lipids Proteins Nucleic acids

Carbohydrates include Small sugar molecules in soft drinks Long starch molecules in pasta and potatoes

Monosaccharides are simple sugars Glucose, found in sports drinks Fructose, found in fruit Honey contains both glucose and fructose Figure 3.8

The monosaccharides glucose and fructose are isomers Their atoms are arranged differently Glucose Fructose Figure 3.9

In aqueous solutions, monosaccharides form rings Monosaccharides are the main fuel that cells use for cellular work (b) Abbreviated ring structure (a) Linear and ring structures Figure 3.10

A disaccharide is a double sugar Disaccharides A disaccharide is a double sugar It is constructed from two monosaccharides

Disaccharides are joined by the process of dehydration synthesis Glucose Glucose Maltose Figure 3.11

The most common disaccharide is sucrose, common table sugar It consists of a glucose linked to a fructose Sucrose is extracted from sugar cane and the roots of sugar beets

The United States is one of the world’s leading markets for sweeteners The average American consumes about 64 kg of sugar per year Figure 3.12

Complex carbohydrates are called polysaccharides They are long chains of sugar units They are polymers of monosaccharides

Polysaccharides Glucose monomer (a) Starch (b) Glycogen (c) Cellulose Starch granules in potato tuber cells (a) Starch Glycogen Granules In muscle tissue (b) Glycogen Cellulose fibril in a plant cell wall Cellulose molecules (c) Cellulose Figure 3.13

One familiar example of a polysaccharide is starch Plant cells store starch for energy Potatoes and grains are major sources of starch in the human diet

Animals store excess sugar in the form of a polysaccharide called glycogen Glycogen is similar in structure to starch

Cellulose is the most abundant organic compound on Earth It forms cable-like fibrils in the tough walls that enclose plants It is a major component of wood It is also known as dietary fiber

Most animals cannot derive nutrition from fiber How do grazing animals survive on a diet of cellulose? They have bacteria in their digestive tracts that can break down cellulose Figure 3.14

Simple sugars and double sugars dissolve readily in water They are hydrophilic, or “water-loving”

Lipids are hydrophobic They do not mix with water Examples: fats and steroids

Dietary fat consists largely of the molecule triglyceride Fats Dietary fat consists largely of the molecule triglyceride A combination of glycerol and three fatty acids Fatty acid Glycerol (a) Dehydration synthesis linking a fatty acid to glycerol Figure 3.15a

Fats perform essential functions in the human body Energy storage Cushioning Insulation

Unsaturated fatty acids Have less than the maximum number of hydrogens bonded to the carbons Saturated fatty acids Have the maximum number of hydrogens bonded to the carbons

(b) A fat molecule Figure 3.15B

Most animal fats have a high proportion of saturated fatty acids Example: butter Most plant oils tend to be low in saturated fatty acids Example: corn oil