Chapter 3- Molecules are building blocks of life Read all figures & legends for comprehension, but pay particular attention to understanding figures 3.3, 3.8, 3.14, 3.18 and 3.27. ******************************************************************* Lecture Notes: Highlighted words are extra vocabulary Carbon has 4 valence electrons so bonds well to others atoms hydrocarbons only C & H covalent bonds energy-rich non-polar functional groups attach tend to react as units have particular properties can be polar contain other atoms Macromolecules large complex assemblies of organic molecules 4 major groups: proteins made of amino acids nucleic acids lipids carbohydrates building macromolecules (all assembled same way) dehydration synthesis form covalent bond betw subunit molecules condensation catalysed by enzymes dehydration requires energy hydrolysis energy is released Function of Proteins -enzyme catalysis globular proteins stress formation of chemical bonds -defense recognize foreign cells & cancer receptors of hormone & immune system -transport oxygen, iron, etc. -support keratin (hair), fibrin (blood clots), collagen (skin, ligaments, tendons & bones) -motion muscles contract due to actin & myocin -regulation intercellular messengers Proteins are made of amino acids polypeptide made of 20 amino acids amino acid has an amino group (-NH2), a carboxyl group (-COOH), a hydrogen and a reactive group all centered on one carbon. five chemical classes: -non-polar -polar uncharged -ionizable -aromatic (contain ring structures) -special-function methionine proline (kinks chain) cysteine (links chains together) can be ionized at both ends (NH3+) (COO-) amino & carboxyl groups can be condensed forms covalent bond known as peptide bond this bond is stiff (does not rotate) A protein's shape determines function of molecule -primary structure a.a. sequence -secondary (due to H bonds between a.a.s) a-helix b-pleated sheets motifs -tertiary 3-D domains structurally independent functional unit e.g., bind different cofactors, etc. -quaternary interactions with other proteins shape determined by molecular chaparones diseases caused by proteins misfolding cystic fibrosis (in some cases) amyloid plaques of Alzheimer's disease proteins unfold (denature) due to: change in environment heat salinity pH different from dissociation (parts break apart) Information Molecules proteins are coded for by information molecules DNA- deoxyribonucleic acid RNA- ribonucleic acid made up of nucleotides -5-carbon sugar -phosphate group -nitrogenous base -purine (2 rings) adenine guanine -pyrimidine cytosine thymine/uracil nucleotide polymer forms when phosphate group binds to hydroxyl group from the sugar sugar-phosphate backbone phosphodiester bonds DNA & RNA: two sugar/phosphate backbones bases that stick out double helices antiparallel held together by H bonds between complementary bases A-T G-C serve as templates for mRNA then proteins Lipids make membranes and store energy Lipids loosely organized group that does not dissolve in water fats and oils high proportion of non-polar C-H bonds -cannot fold up to hide away nonpolar parts from water -lipids spontaneouly assemble and expose polar parts to water this characteristic important in cell membranes phospholipids form core of cell membranes (will see in Ch. 6) composite molecules: glycerol 3 carbon alcohol each with H attached fatty acids nonpolar "tails" long chains of C-H bonds, ending in carboxyl group (-COOH) phosphate group polar "head" of phospholipid at one end of glycerol usually has charged molecule attached fats (triglyceride or triacylglycerol) do not have polar end glycerol molecule + 3 fatty acids 3 fatty acids may differ from each other C-H bonds store fats spontaneously clump together in water fatty acids hydrocarbon chains vary in length even numbers (14-20) most common saturated (ex: butter) if all carbons have at least two H atoms molecules align 'hard fat' all animal fats are saturated except some fish oil unsaturated double bonds exist betw carbons most plant fats except palm & coconut oils polyunsaturated (ex: corn oil) if more than one double bond betw carbons chains bend at double bonds molecules cannot align these fats have low melting points other lipids terpenes long-chain lipids common in plants (ex: rubber) steroids 4 carbon rings hormones prostaglandins modified fatty acids with 2 nonpolar tails and 5-carbon ring. local chemical messengers in verts fats as food energy is stored in C-H bonds most fats have over 40 Cs. yield 9 cals/gram oil can become solid if add Hydrogens hydrogenated fats are as bad for you as saturated fats excess carbs are converted into fats in animals plaques can adhere to blood vessels leading to strokes when break off Carbohydrates store energy and provide building materials Carbohydrates contain carbon, hydrogen & oxygen (1:2:1) energy-storage molecules & structural elements simple carbs monosaccharides (simple sugars) usually 6 carbons (i.e., GLUCOSE) usually form rings in water isomers of glucose structural isomer fructose stereoisomer galactose can have substantial differences in physical properties disaccharides two sugars joined by covalent bond role in transport of sugars polysaccharides monosaccharide subunits i.e., starch, used to store energy in plants glucose linked in long chains i.e., cellulose, used for structure in plants glucose linked in long chains can only be broken by special enzymes linked sugars transport disaccharides glucose transported as simple sugar in humans transported as disaccharide in plants and other organisms means less available for use while being transported glucose + fructose = sucrose glucose + galactose = lactose cleaved by lactase lacking in many adult animals storage polysaccharides metabolic energy stored in linked disaccharides i.e., maltose insoluble, deposited in storage long polymers made by dehydration synthesis starches plant polysaccharides from glucose energy sources available when links are hydrolyzed amylose a longer form of maltose insoluble in long chains because it coils up shorter forms more soluble broken down by cooking potatoes enzymes break down to maltose then to glucose cells can metabolize amylopectic branched amylose also insoluble glycogen animal polysaccharides from branched amylose stored in liver & muscle retrieved as glucose insoluble more branches & longer chains than in starches left-handed sugars mirror-image of real sugars body cannot metabolize so they taste sweet, but cannot become fat structural carbohydrates cellulose glucose has two forms alpha-hydroxyl group below ring chain forms starch beta-hydroxyl group above ring chain forms cellulose few organisms can break down cellulose commonly used structural material cows & bacteria chitin modified cellulose extra nitrogen group forms insect exoskeletons