Lecture 4 - Biological Molecules Part I

Lecture 4: Biological Molecules

BIOL 211 Spring 2012

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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

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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 “Macro” • Molecular structure dictates function = “large”

All four classes are organic molecules! Not all organic molecules are part of one of the four classes of biological molecules! BIOL 211 Spring 2012

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What do macromolecules look like?


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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


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• 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


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Polymers and monomers (of both nonbiological type)

Monomer Polymer


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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


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Kevlar

Polyethylene


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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


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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 2

1

3

4

Hydrolysis adds a water molecule, breaking a bond.

1

2

3 BIOL 211 Spring 2012

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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

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Examples of carbohydrates • Sugar, starch, cellulose, glucose


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Sugars

Carbo = carbon, Hydrate = water

• Monosaccharides have molecular formulas that are usually multiples of CH2O • Glucose (C6H12O6) 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


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Structure of carbohydrates • Composed of carbon, hydrogen, and oxygen • Though often drawn as linear skeletons, in aqueous solutions many sugars form rings


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Figure 5.3 Aldoses (Aldehyde Sugars)

Ketoses (Ketone Sugars)

Trioses: 3-carbon sugars (C3H6O3)

Glyceraldehyde

Dihydroxyacetone

Pentoses: 5-carbon sugars (C5H10O5)

Ribose

Ribulose

Hexoses: 6-carbon sugars (C6H12O6)

Glucose

Galactose

Fructose


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Figure 5.4

1 2

6

6

5

5

3 4

4 5

1

3

2

4

1 3

2

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(a) Linear and ring forms

6 5 4

1

3

2

(b) Abbreviated ring structure

(c) Chair structure


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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

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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

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Two forms of glucose: alpha () and beta () • Cis-trans isomers


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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

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A glycosidic bond/linkage joins a carbohydrate to another group, which may or may not be another carbohydrate BIOL 211 Spring 2012

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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

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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?


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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


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Examples of polysaccharides • Storage – Starch • Two types of plant starches: amylopectin and amylose

– Glycogen • Branched chains of glucose found in animals


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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

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Figure 5.6

Chloroplast

Starch granules Amylopectin

Amylose (a) Starch: a plant polysaccharide Mitochondria

1 m

Glycogen granules

Glycogen (b) Glycogen: 0.5 m an animal polysaccharide BIOL 211 Spring 2012

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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 ()


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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


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Why is  glucose used in cellulose?


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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


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Structural polysaccharides • Chitin is in the exoskeleton of arthropods and the cell walls of many fungi


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What are the two main types of polysaccharides? What are some examples of each?


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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


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Examples of lipids • Oils, fats, phospholipids, steroids


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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


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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

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• 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


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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


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Unsaturated Fats • Includes polyunsaturated and monounsaturated fats on nutrition labels 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


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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


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Saturated fat

The fatty acid tails can freely rotate around the glycerol head Monounsaturated fat

Polyunsaturated fat


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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 CH3

Cis form

Pentene Trans form BIOL 211 Spring 2012

CH3

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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

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Why so bad for you? Why are saturated fats so bad for you vs. unsaturated fats? Why are trans fats particularly unhealthy?


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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


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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


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The smell of bruised leaves and cucumbers both come from phospholipid fragments


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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

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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?


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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

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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

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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?


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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


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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


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Cholesterol as a chemical precursor Cholesterol

Enzymatic reactions


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Birth control pills

If an egg has been fertilized, estrogen and progesterone levels remain high


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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

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Describe/draw the structure and function of the three main types of lipids Fats

Phospholipids

Steroids

Structure

Function


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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


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Questions?


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Lecture 4 - Biological Molecules Part I

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