The Molecules of Life

The Molecules of Life Chapter 3 Part II

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

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

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

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

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

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

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)

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

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

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)

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

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

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’

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?

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

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

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

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

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

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

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

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

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

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

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

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

The Molecules of Life