The Molecules of Life

1. The Molecules of Life Chapter 3 Part II

2. Monosaccharides • Monosaccharides, especially glucose, are the main fuel molecules for cellular work • Cells break down glucose molecules extract their stored energy - gives off carbon dioxide as ‘exhaust’ • Monosaccharides provide our cells with carbon skeletons to be used as raw material - manufacturing other kinds of organic molecules

3. Honey • Sweet taste comes from the 2 main ingredients – fructose and glucose Figure 3.7

4. Disaccharides • A double sugar built from 2 monosaccharides joined together by a dehydration reaction - Maltose made from 2 glucose monomers - Lactose made from 1 glucose and 1 galactose monomers • Lactose intolerance – inability to break down or ‘digest’ the milk sugar lactose • Sucrose, common table sugar, consists of glucose + fructose - main carbohydrate in plant sap - nourishes all the parts of the plant - extracted from the stems of sugarcane or the roots of sugar beets

5. Disaccharide Formation 2 simple sugars joined by a dehydration reaction, form a bond between the sugar monomers Figure 3.10

6. Disaccharides • Lactase - enzyme • Americans consume ~ 64kg (140 lb) of sweetener per person per year Figure 3.11, 3.12

7. Processed Sugar • Through a commercial process natural sucrose in corn syprup is converted into the much sweeter fructose - high-fructose corn syrup (HFCS) - soft drinks HFCS is the 1st or 2nd ingredient listed • High sugar consumption is a national growing health issue • For good health we require proteins, fats, vitamins, and minerals and a substantial amount of complex carbohydrates

8. Polysaccharides • Complex carbohydrates are called polysaccharides - long chains (polymers) of sugar units of monosaccharides • Starch, a familiar example consists of many glucose monomers strung together - found in roots and other plant organs - plant cells store starch in granules to be used as needed - provides energy and raw material • Major sources of starch in the human diet include: - potatoes and grains (i.e. corn, wheat, rice)

9. Glycogen • Animals store excess sugar in the form of glycogen similar in structure to starch - a polymer of glucose monomers - but is more extensively branched • Glycogen is mostly stored as granules in our liver and muscle cells - breaks down glycogen to release glucose as needed - basis for ‘carbo loading’ starchy foods consumed the night before is converted to glycogen for rapid use the next day • In addition to nutrition some polysaccharides serve as structural components

10. Cellulose • Cellulose, the most abundant organic compound on Earth - forms cable-like fibrils in a plant cell wall - is the major component of wood - resembles starch and glycogen but its glucose monomers are linked in a different orientation - glucose linkage cannot be broken by most animals • Cellulose in plant foods is known as dietary ‘fiber’ or ‘roughage’ - passes through our digestive system unchanged - prokaryotes in digestive tracts of grazing animals break down cellulose - it is not a nutrient but is essential to keep our digestive system healthy

11. Polysaccharrides Figure 3.13 Plants store glucose by polymerizing it in the form of starch Structural polysaccharide – i.e. cellulose of plant cell walls Cellulose molecules assembled into fibrils make up the tree walls Animals store glucose In the form of glycogen (more branched)

12. Prokaryotes in Grazing Animals • Prokaryotes break down cellulose by converting it to glucose monomers that the cow can digest • The by-product of this reaction is large amounts of methane Figure 3.14

13. Hydrophilic Molecules • Monosaccharides (i.e. glucose or fructose) and disaccharides (i.e. sucrose or lactose) dissolve readily in water • Cellulose and some forms of starch do not dissolve in water • Most carbohydrates are hydrophilic or ‘water-loving’ - hydrophilic molecules adhere water to their surface

14. Low-Carb Diets • Majority of calories in a typical American diet come from carbohydrates • In recent years, ‘low-carb diets’ have become popular - cutting carbs equates to cutting calories - consumers need to be wary of products saying they are ‘low-carb’

15. Checkpoint • Draw a structural formula for C2H4 • When 2 glucose molecules are joined together in a dehydration reaction, what are the formulas of the 2 products. • Why do the monosaccharides glucose and fructose with the same molecular formula have different properties • How do manufacturers produce the HFCS listed as an ingredient on a soft drink bottle. Why is this profitable?

16. C=C Answers 1. 2. C6H12O6 + C6H12O6  C12H22O11 + H2O 3. 4. A commercial process converts glucose in the syrup to the much sweeter fructose. Less syrup has to be used = save money

17. Lipids • Lipids are hydrophobic - do not mix with water • Lipids are a diverse set of molecules - includes fats and steroids • Dietary fat consists largely of triglyceride molecules - a glycerol molecule + 3 fatty acid molecules • Long hydrocarbon portion stores a lot of energy - like the hydrocarbons of gasoline stores a lot of energy - a pound of fat has 2X as much energy as a pound of carbs - downside to this energy efficiency is the difficulty in ‘burning off’ excess body fat

18. Glycerol ‘head’ + 3 fatty acid ‘tails of long hydrocarbons Fig 3.15a

19. Lipids • Fats perform essential functions in the human body: - energy storage; cushioning; insulation • Energy storage - an appropriate amount of body fat is both normal and healthy as a fuel reserve - stored in reservoirs known as adipose cells that swell when we deposit and shrink when we withdraw fat for energy • Cushioning - adipose tissue cushions vital organs • Insulation - helps maintain a warm body temperatureeven in the cold

20. Unsaturated and Saturated Fatty Acids Figure 3.15b • Unsaturated = double bond in the carbon skeleton • Saturated = lack double bonds and so have the maximum amount of hydrogen atoms • Polyunsaturated has several double bonds within its fatty acids

21. Saturated and Unsaturated Fatty Acids • Most animal fats have a high proportion of saturated fatty acids, which can be unhealthy - such as lard and butter - linear shape of saturated fatty acid allows them to stack and so they are solid at room temperature • Most plant oils tend to be low in saturated fatty acids - such as corn and canola oil; also fish oil - bent shape doesn’t allow them to stack easily and so they are usually liquid at room temperature - tropical plant oils are an exception - cocoa butter has both types with a melting point near body temperature

22. Atherosclerosis • Increased risk of heart attacks and strokes • Plague, lipid-containing deposits build up within blood vessel walls • Reduction of bloodflow

23. Healthy fats rich in omega-3 fatty acids Some fats perform important functions in the body and are essential to a healthy diet Fig 3.16

24. Hydrogenation • Manufacturers convert unsaturated fats to saturated fats by adding hydrogen - creates trans fat, that is even more unhealthy - longer shelf life - peanut butter • FDA now requires trans fats to be listed in the nutrition label of all foods containing them

25. Steroids • Classified as lipids because they are hydrophobic - different in both structure and function • Carbon skeleton is bent to form 4 fused rings - cholesterol is a steroid and is an essential molecule • Cholesterol is the base steroid from which your body produces other steroids - estrogen and testosterone

26. Different steroids vary in the functional groups attached to the core set of rings, these variations affect their function Figure 3.17

27. Anabolic Steroids –Synthetic Variant of Testosterone - Testosterone causes a general buildup of muscle and bone mass during puberty - Some athletes use anabolic steroids to build up their muscles and enhance their performance Figure 3.18