Lecture 4: Biological Molecules BIOL 211 Spring 2012 1
In this lecture Macromolecules Monomers and polymers The four classes of biological molecules Lipids Saturated, unsaturated, trans fats Phospholipids Steroids Carbohydrates Monosaccharides, disaccharides, polysaccharides Proteins Amino acids Primary, secondary, tertiary, quarternary structure Nucleic acids Nucleotides DNA and RNA BIOL 211 Spring 2012 2
The four classes of biological molecules All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids These are macromolecules - large molecules composed of thousands of covalently connected atoms Molecular structure dictates function All four classes are organic molecules! Not all organic molecules are part of one of the four classes of biological molecules! Macro = large BIOL 211 Spring 2012 3
What do macromolecules look like? BIOL 211 Spring 2012 4
What do they do? Type of macromolecule Example Function Lipids Fat Cell membranes, energy storage Carbohydrates Starch, sugar Energy storage, structure Nucleic acids DNA, RNA Store genetic material Proteins Trypsin Cell machinery BIOL 211 Spring 2012 5
Polymer - a long molecule consisting of many similar building blocks Monomer the building block Three of the four classes of life s organic molecules are polymers Carbohydrates Proteins Nucleic acids BIOL 211 Spring 2012 6
Polymers and monomers (of both nonbiological type) Monomer Polymer BIOL 211 Spring 2012 7
Polymers and monomers (of the nonbiological type) Nylon monomer Nylon polymer A monomer is a single pattern repeated over and over. It can be composed of many atoms Nylon polymer BIOL 211 Spring 2012 8
Kevlar Polyethylene BIOL 211 Spring 2012 9
Creating and breaking down polymers Dehydration/condensation reaction - two monomers bond together through the loss of a water molecule Hydrolysis two bonded monomers split apart using a water molecule BIOL 211 Spring 2012 10
Figure 5.2 (a) Dehydration reaction: synthesizing a polymer 1 2 3 Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond. 1 2 3 4 Longer polymer (b) Hydrolysis: breaking down a polymer 1 2 3 4 Hydrolysis adds a water molecule, breaking a bond. 1 2 3 BIOL 211 Spring 2012 11
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Class I: Carbohydrates Sugars and the polymers of sugars Simplest carbohydrate monomers are monosaccharides More complex carbohydrate polymers are called polysaccharides Purpose: fuel and fuel storage, building material Sugar Cellulose BIOL 211 Spring 2012 13
Examples of carbohydrates Sugar, starch, cellulose, glucose BIOL 211 Spring 2012 14
Sugars Carbo = carbon, Hydrate = water Monosaccharides have molecular formulas that are usually multiples of CH 2 O Glucose (C 6 H 12 O 6 ) is the most common monosaccharide Monosaccharides are classified by The location of the carbonyl group (as aldose or ketose) The number of carbons in the carbon skeleton 3, 5, or 6 carbons BIOL 211 Spring 2012 15
Structure of carbohydrates Composed of carbon, hydrogen, and oxygen Though often drawn as linear skeletons, in aqueous solutions many sugars form rings BIOL 211 Spring 2012 16
Figure 5.3 Aldoses (Aldehyde Sugars) Ketoses (Ketone Sugars) Trioses: 3-carbon sugars (C 3 H 6 O 3 ) Glyceraldehyde Dihydroxyacetone Pentoses: 5-carbon sugars (C 5 H 10 O 5 ) Ribose Ribulose Hexoses: 6-carbon sugars (C 6 H 12 O 6 ) Glucose Galactose Fructose BIOL 211 Spring 2012 17
Figure 5.4 1 6 6 2 5 5 3 4 4 1 4 1 5 3 2 3 2 6 (a) Linear and ring forms 6 5 4 1 3 2 (c) Chair structure (b) Abbreviated ring structure BIOL 211 Spring 2012 18
Monosaccharides Some common carbohydrate monomers Fructose Fruit sugar Glucose Produced by photosynthesis, used as energy storage Ribose Important in RNA (ribonucleic acid) Glucose BIOL 211 Spring 2012 19
High fructose corn syrup Primary sweetener in the U.S. due to corn subsidies and foreign sugar tariffs FDA says GRAS, but still health concerns on the rise Normal corn syrup is all glucose Enzymatic processing converts glucose into fructose HFCS is 24% water, the rest sugar 55% fructose, 45% glucose HFCS used in soda Fructose is much sweeter than glucose BIOL 211 Spring 2012 20
Two forms of glucose: alpha ( ) and beta ( ) Cis-trans isomers BIOL 211 Spring 2012 21
2 Disaccharides Two monosaccharides bond together using a dehydration reaction to create a disaccharide The bond between two monosaccharides is called a glycosidic bond Examples of disaccharides: Sucrose Table sugar Lactose Sugar found in milk Maltose The enzyme amylase breaks down starch to produce maltose Mashing is a step in beer fermentation where amylase produces maltose from the plant starch in barley BIOL 211 Spring 2012 22
A glycosidic bond/linkage joins a carbohydrate to another group, which may or may not be another carbohydrate BIOL 211 Spring 2012 23
Lactose intolerance Inability to digest the sugar in milk Caused by a lack of the enzyme lactase, which hydrolyzes lactose into its monosaccharides glucose and galactose Bacteria in your gut can metabolize it through fermentation though, which produces hydrogen, carbon dioxide, and methane BIOL 211 Spring 2012 24
Sucrose intolerance is a rare metabolic disorder characterized by the lack of ability to break down the disaccharide sucrose - What sort of diet would someone with sucrose intolerance have to follow? - What happens if someone with sucrose intolerance were to eat something containing sugar? BIOL 211 Spring 2012 25
Many Polysaccharides Many monosaccharides linked together through glycosidic bonds The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic bonds Two types of polysaccharides: storage and structural BIOL 211 Spring 2012 26
Examples of polysaccharides Storage Starch Two types of plant starches: amylopectin and amylose Glycogen Branched chains of glucose found in animals BIOL 211 Spring 2012 27
Storage polysaccharides Starch, a storage polysaccharide of plants, consists entirely of glucose monomers joined by glycosidic bonds Stores energy in the potential chemical energy in the bonds of carbohydrates Plants store surplus starch as granules within organelles as amylose and amylopectin Animals also store starch in the form of glycogen in liver and muscle cells The simplest form of starch is amylose BIOL 211 Spring 2012 28
Figure 5.6 Chloroplast Starch granules Amylopectin (a) Starch: a plant polysaccharide 1 m Amylose Mitochondria Glycogen granules (b) Glycogen: 0.5 m an animal polysaccharide BIOL 211 Spring 2012 Glycogen 29
Structural polysaccharides The polysaccharide cellulose is a major component of the tough wall of plant cells Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ The difference is based on two ring forms for glucose: alpha ( ) and beta ( ) BIOL 211 Spring 2012 30
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Polymers with glucose are helical Polymers with glucose are straight In straight structures, H atoms on one strand can hydrogen bond with OH groups on other strands Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants BIOL 211 Spring 2012 32
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Why is glucose used in cellulose? BIOL 211 Spring 2012 34
What is fiber? Enzymes that digest starch by hydrolyzing linkages can t hydrolyze linkages in cellulose Cellulose in human food passes through the digestive tract as insoluble fiber Some microbes use enzymes to digest cellulose Many herbivores, from cows to termites, have symbiotic relationships with these microbes BIOL 211 Spring 2012 35
Structural polysaccharides Chitin is in the exoskeleton of arthropods and the cell walls of many fungi BIOL 211 Spring 2012 36
What are the two main types of polysaccharides? What are some examples of each? BIOL 211 Spring 2012 37
Class 2: The only class that does not form polymers Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bonds The most biologically important lipids are fats, phospholipids, and steroids Purpose: fuel storage, cell membranes BIOL 211 Spring 2012 38
Examples of lipids Oils, fats, phospholipids, steroids BIOL 211 Spring 2012 39
Fats Two components: glycerol and 3 fatty acids The major function of fats is energy storage Glycerol is a threecarbon alcohol with a hydroxyl group attached to each carbon A fatty acid consists of a carboxyl group attached to a long carbon skeleton The hydrogen on this hydroxyl group can pop off in water. Since the molecule is donating a hydrogen, it is classified as an acid BIOL 211 Spring 2012 40
Synthesis of fats In a fat, three fatty acids are joined to glycerol by an ester linkage Generic ester functional group form: O = R - C O C R This creates a triacylglycerol, AKA triglyceride In cooking, fats break apart into smaller molecules that produce the characteristic deep fried smell BIOL 211 Spring 2012 41
Fatty acids vary in length (number of carbons) and in the number and locations of double bonds Usually 4-35 carbons long Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds Each carbon saturated with hydrogens Unsaturated fatty acids have one or more double bonds BIOL 211 Spring 2012 42
Saturated fats The straight hydrocarbon chains stack very closely together (Think of straight pencils in a box) Because they are so densely packed, saturated fats tend to be solid at room temp BIOL 211 Spring 2012 43
Includes polyunsaturated and monounsaturated fats on nutrition labels Unsaturated Fats The double bond kinks the hydrocarbon chain and forces it to bend The hydrocarbon chains don t stack so easily, and so are less dense. Unsaturated fats tend to be liquid at room temp BIOL 211 Spring 2012 44
Polyunsaturated and Monounsaturated Fats Monounsaturated fats have only one carbon-carbon double bond Polyunsaturated fats have two more more carbon-carbon double bonds Certain unsaturated fatty acids are not synthesized in the human body, and must be supplied in the diet These essential fatty acids include the omega-3 fatty acids, required for normal growth, and thought to provide protection against cardiovascular disease Poly = many Mono = one BIOL 211 Spring 2012 45
Saturated fat The fatty acid tails can freely rotate around the glycerol head Monounsaturated fat Polyunsaturated fat BIOL 211 Spring 2012 46
Trans fats Produced by artificially saturating unsaturated fats by adding hydrogen hydrogenation Nickel is added to unsaturated liquid oil as a catalyst The mix is exposed to high temperature and pressure as hydrogen gas is pumped through Nickel is filtered out Hydrogenation also straightens the kinks in unsaturated fats, isomerizing from cis to trans form Cis form CH 3 Pentene Trans form CH 3 BIOL 211 Spring 2012 47
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Why hydrogenate fats? Saturated fats tend to be solid at room temp In baked goods, saturated fats produce a much better mouth feel and texture than unsaturated fats Cheaper to hydrogenate the polyunsaturated fats in vegetable oil than acquire natural saturated fats from animal sources Saturated fats are more stable than unsaturated fats Beef has a longer shelf life than pork or chicken because it has a larger proportion of saturated fats Partially hydrogenated vegetable oil: some of the carbon-carbon double bonds are hydrogenated, but not all BIOL 211 Spring 2012 49
Why so bad for you? Why are saturated fats so bad for you vs. unsaturated fats? Why are trans fats particularly unhealthy? BIOL 211 Spring 2012 50
Why so bad for you? A group of identical and regular molecules fits together more neatly than different and irregular molecules Triglycerides circulate in your blood. Saturated and trans fats clump together much more easily in your blood vessels, forming plaque that blocks arteries BIOL 211 Spring 2012 51
Phospholipids Phospholipids are the major component of all cell membranes Four components: glycerol, phosphate group, choline, 2 fatty acids The two fatty acid tails are hydrophobic, but the phosphate, glycerol, and choline form a hydrophilic head The entirety of a fat molecule is hydrophobic BIOL 211 Spring 2012 52
The smell of bruised leaves and cucumbers both come from phospholipid fragments BIOL 211 Spring 2012 53
Phospholipids: the secrets of cell membranes When added to water, phospholipids self-assemble into a bilayer, with the hydrophobic tails pointing toward the interior The structure of phospholipids results in a bilayer arrangement found in cell membranes BIOL 211 Spring 2012 54
The notothenoids are a type of bony fish living in Antarctica. The waters they inhabit range from -2C to 4C. What would you expect the composition of their cell membranes to be like? BIOL 211 Spring 2012 55
Phospholipids in drug delivery Outside the cell A big problem in medicine is how to get drugs inside cells where they can then act Phospholipids can be coaxed to form a hollow droplet called a liposome Liposomes are filled with a drug of interest Inside the cell Phospholipid liposomes merge smoothly with the phospholipid cell wall, depositing their contents into the interior of the cell BIOL 211 Spring 2012 56
Phospholipids in food The smell of bruised leaves and cut cucumbers comes from phospholipid fragments Eggs are an abundant source of the phospholipid lecithin Eggs are used to produce stable mixtures of fats and water Mayonnaise Custards Hollandaise sauce BIOL 211 Spring 2012 57
Eggs are an abundant source of the phospholipid lecithin, and also a crucial ingredient in mayonnaise, a smooth blend of fat and water. How do eggs contribute to the smooth blending of fat and water? BIOL 211 Spring 2012 58
Steroids Steroids are lipids characterized by a carbon skeleton consisting of four fused rings Cholesterol, an important steroid, is a component in animal cell membranes BIOL 211 Spring 2012 59
Cholesterol: not such a bad guy? Too much cholesterol can damage cell walls and cause atherosclerosis Cholesterol stiffens animal cell membranes OH group interacts with polar region, cyclic rings embed within nonpolar region Cholesterol draws fatty acid chains together, more densely packing phospholipids and stiffening cell membranes BIOL 211 Spring 2012 60
Cholesterol as a chemical precursor Cholesterol Enzymatic reactions BIOL 211 Spring 2012 61
Birth control pills If an egg has been fertilized, estrogen and progesterone levels remain high BIOL 211 Spring 2012 62
Steroids in medicine Corticosteroids: used to treat a huge array of diseases and symptoms Anabolic steroids: mimic the effect of testosterone Increase the rate of protein synthesis in cells Result in increased muscle mass and secondary sex characteristics Excess testosterone converted to estradiol, which causes gynomastia in men Natural testosterone synthesis is suppressed, resulting in testicular atrophy and reduced sperm production BIOL 211 Spring 2012 63
Describe/draw the structure and function of the three main types of lipids Structure Fats Phospholipids Steroids Function BIOL 211 Spring 2012 64
Looking back at this picture, what sorts of carbohydrates and lipids would you expect to find in strawberries? Keep in mind: - Plant cell wall composition - Presence of lipids in seeds and cell walls - Presence of sugars BIOL 211 Spring 2012 65
Questions? BIOL 211 Spring 2012 66