AP Biology Chapter 3: Structure and Function of Macromolecules (Independently brush up on Ch 2 and Ch 3.1)

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 repeating building blocks in a chain monomers building blocks repeated small units covalent bonds H2O HO H

How to build a polymer Synthesis joins monomers by “taking” H2O out one monomer donates OH– other monomer donates H+ together these form H2O requires energy & enzymes H2O HO H enzyme Condensation reaction - two molecules join, lose a smaller one Dehydration synthesis - Condensation reaction, in which the lost molecule = H2O

Dehydration Synthesis

How to break down a polymer Digestion use H2O to breakdown polymers reverse of dehydration synthesis cleave off one monomer at a time H2O is split into H+ and OH– H+ & OH– attach to ends requires hydrolytic enzymes releases energy H2O HO H enzyme Hydrolysis Digestion

Discussion Under what circumstances would you expect to find a cell conducting a great deal of dehydration synthesis? In which organs or under what circumstances would you expect to find body cells conducting hydrolysis?

Variety of Polymers Every cell has thousands of varieties of macromolecules These molecules are constructed from only 40 to 50 common monomers Analogy: 26 letters of the alphabet can be combined to form millions of words Shortcoming: macromolecules are much longer than the average word and they can be branched or 3D.

Carbohydrates

Carbohydrates a.k.a. wheeee energy! :D

Carbohydrates are composed of C, H, O CH2O)x C6H12O6 Function: energy u energy storage raw materials u structural materials Monomer: sugars (monosaccharide) (CH2O)x C6H12O6 sugar

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

Sugar structure 5C & 6C sugars form rings in solution

You’ll see this come back in our DNA unit… Numbered carbons You’ll see this come back in our DNA unit… C 6' C O 5' C C 4' 1' energy stored in bonds C C 3' 2'

Simple & complex sugars Monosaccharides simple 1 monomer sugars Ex: glucose Disaccharides 2 monomers Ex: sucrose Polysaccharides 3+ monomers Ex: starch, cellulose, glycogen

Building sugars Dehydration synthesis monosaccharides disaccharide | H2O | glucose | fructose | sucrose (table sugar) sucrose = table sugar

Polysaccharides Polymers of sugars Functions: costs little energy to build easily reversible = release energy Functions: energy storage starch (plants) glycogen (animals) in liver & muscles structure cellulose (plants) chitin (arthropods & fungi)

Polysaccharide diversity Molecular structure determines function - a major theme! in starch in cellulose Isomers of glucose Different structure = connect to the next monomer in the chain differently = different 3D structure. Starch - helical. Cellulose - straight, with free OH to bond to neighboring celluloses = rigid structure!

Cellulose Most abundant organic compound on Earth herbivores have evolved a mechanism to digest cellulose most carnivores have not that’s why they eat meat to get their energy & nutrients cellulose = undigestible roughage 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.

Helpful bacteria How can herbivores digest cellulose so well? BACTERIA live in their digestive systems & help digest cellulose-rich (grass) meals Ruminants

Discussion In EXACTLY 20 words, summarize the most important point or points to remember about carbohydrates.

Lipids: Fats & Oils

Lipid Primary Function: long term energy storage concentrated energy

Lipids Lipids are composed of C, H, O “Family groups” Same as carbohydrates, but different structure = different function! Lipids are composed of C, H, O long hydrocarbon chains (H-C) “Family groups” fats phospholipids steroids Do not form polymers big molecules made of smaller subunits not a continuing chain

dehydration synthesis Fats Structure: glycerol (3C alcohol) + fatty acid fatty acid = long HC “tail” with carboxyl (COOH) group “head” enzyme H2O dehydration synthesis

Building Fats Triacylglycerol 3 fatty acids linked to glycerol ester linkage between OH & COOH hydroxyl carboxyl BIG FAT molecule!!

Dehydration synthesis H2O dehydration synthesis enzyme H2O Pulling the water out to free up the bond enzyme H2O enzyme H2O

Discussion What kind of molecule would you expect to be hydrophobic - polar or non-polar? Why? Do you think lipids (such as fats, oils, waxes) are probably polar or non-polar?

Fats store energy Long HC chain Functions: polar or non-polar? hydrophilic or hydrophobic? Functions: energy storage 2x carbohydrates cushion organs membranes & waterproofing insulates body think whale blubber!

Discussion Show me a human who doesn’t want to eat this and I’ll show you a LIAR. Knowing their major functions, hypothesize: what occurred in evolutionary history that led to humans enjoying the tastes of fatty and sugary foods?

Structure & Function Saturated Fats All C bonded to H No C=C double bonds long, straight chain most animal fats solid at room temp. contributes to cardiovascular disease (atherosclerosis) = plaque deposits Mostly animal fats

Structure & Function Unsaturated Fats C=C double bonds in the fatty acids plant & fish fats vegetable oils liquid at room temperature the kinks made by double bonded C prevent the molecules from packing tightly together Mostly plant lipids Think about “natural” peanut butter: Lots of unsaturated fats Oil separates out Companies want to make their product easier to use: Stop the oil from separating Keep oil solid at room temp. Hydrogenate it = chemically alter to saturate it Affect nutrition?

Discussion Unsaturated fats are widely considered to be healthier (sometimes called “good fats” for short) than saturated fats. Why might this be? (Hint: think of their structures, and what they might mean for how easily the body would use them for energy vs. storing them in fat cells)

Phospholipids Structure: glycerol + 2 fatty acids + PO4 PO4 = negatively charged

Phospholipids Hydrophobic or hydrophilic? fatty acid tails = PO4 head = split “personality” interaction with H2O is complex & very important!

Phospholipids in water heads H2O tails H2O can self-assemble into “bubbles” called micelles can also form a phospholipid bilayer Early Earth history - a cell part that self-assembles! bilayer

Why is this important? Phospholipids create a barrier in water define outside vs. inside they make cell membranes!

Steroids Structure: 4 fused C rings + ?? different steroids created by attaching different functional groups to rings different structure creates different function examples: cholesterol, sex hormones cholesterol

Cholesterol Important cell component animal cell membranes precursor of all other steroids including vertebrate sex hormones high levels in blood may contribute to cardiovascular disease

Cholesterol Important component of cell membrane helps keep cell membranes fluid & flexible

From Cholesterol  Sex Hormones What a big difference a few atoms can make! Same C skeleton, different functional groups

Discussion In EXACTLY 20 words, summarize the most important point or points to remember about lipids.