Chapter 5. Macromolecules

Macromolecules Smaller organic molecules join together to form larger molecules macromolecules 4 major classes of macromolecules: carbohydrates lipids proteins nucleic acids

Polymers Long molecules built by linking chain of repeating smaller units polymers monomers = repeated small units covalent bonds • great variety of polymers can be built from a small set of monomers • monomers can be connected in many combinations like the 26 letters in the alphabet can be used to create a great diversity of words • each cell has millions of different macromolecules

How to build a polymer Condensation reaction dehydration synthesis joins monomers by “taking” H2O out 1 monomer provides OH the other monomer provides H together these form H2O requires energy & enzymes

How to break down a polymer Hydrolysis use H2O to break apart monomers reverse of condensation reaction H2O is split into H and OH H & OH group attach where the covalent bond used to be ex: digestion is hydrolysis Most macromolecules are polymers • build: condensation (dehydration) reaction • breakdown: hydrolysis An immense variety of polymers can be built from a small set of monomers

Carbohydrates

So what’s all this talk about carbs? Atkin’s Diet South Beach Diet

Carbohydrates are composed of C, H, O carbo - hydr - ate (CH2O)x C6H12O6 Function: energy u energy storage raw materials u structural materials Monomer: sugars ex: sugars & starches carb = caron hydr = hydrogen ate = oxygen compound

Sugars Most names for sugars end in -ose Classified by number of carbons 6C = hexose (glucose) 5C = pentose (fructose, ribose) 3C = triose (glyceraldehyde)

What functional groups? carbonyl aldehyde ketone hydroxyl

Sugar structure 5C & 6C sugars form rings in aqueous solutions in cells! Carbons are numbered

Numbered carbons C 6' C O 5' C C 4' 1' C C 3' 2'

Simple & complex sugars Monosaccharides simple 1 monomer sugars glucose Disaccharides 2 monomers sucrose Polysaccharides large polymers starch

Building sugars Dehydration synthesis monosaccharides disaccharide | maltose | glucose | glucose | maltose glycosidic linkage

Building sugars Dehydration synthesis monosaccharides disaccharide | sucrose = table sugar | glucose | fructose | sucrose structural isomers glycosidic linkage

Polysaccharides Polymers of sugars Function: costs little energy to build easily reversible = release energy Function: energy storage starch (plants) glycogen (animals) building materials = structure cellulose (plants) chitin (arthropods & fungi) Polysaccharides are polymers of hundreds to thousands of monosaccharides

Branched vs linear polysaccharides Can you see the difference between starch & glycogen? Which is easier to digest? Glycogen = many branches = many ends Enzyme can digest at multiple ends. Animals use glycogen for energy storage == want rapid release. Form follows function.

Polysaccharide diversity Molecular structure determines function isomers of glucose How does structure influence function…

Digesting starch vs. cellulose Starch = all the glycosidic linkage are on same side = molecule lies flat Cellulose = cross linking between OH (H bonds) = rigid structure

Cellulose Most abundant organic compound on Earth Cross-linking between polysaccharide chains: = rigid & hard to digest The digestion of cellulose governs the life strategy of herbivores. Either you do it really well and you’re a cow or an elephant (spend a long time digesting a lot of food with a little help from some microbes & have to walk around slowly for a long time carrying a lot of food in your stomach) Or you do it inefficiently and have to supplement your diet with simple sugars, like fruit and nectar, and you’re a gorilla.

Glycemic index Which food will get into your blood more quickly? apple rice cakes corn flakes bagel peanut M&M

Glycemic index Ranking of carbohydrates based on their immediate effect on blood glucose (blood sugar) levels Carbohydrate foods that breakdown quickly during digestion have the highest glycemic indices. Their blood sugar response is fast & high.

Glycemic index Which food will get into your blood more quickly? apple 36 rice cakes 82 corn flakes 84 bagel 72 peanut M&M 33 Why do we find sweet foods pleasurable to eat? Why are we attracted to sweet food?

Let’s build some Carbohydrates!