The Chemicals of Life Part 1

Why study Carbon? All living things are made of cells Cells ~72% H2O ~3% salts (Na, Cl, K…) ~25% carbon compounds carbohydrates lipids proteins nucleic acids Why do we study carbon -- is it the most abundant element in living organisms? H & O most abundant C is the next most abundant

Chemistry of Life Organic chemistry is the study of carbon compounds (in living things) C atoms are versatile building blocks bonding properties 4 stable covalent bonds Carbon chemistry = organic chemistry Why is it a foundational atom? What makes it so important? Can’t be a good building block if you only form 1 or 2 bonds.

Hydrocarbons Simplest C molecules = hydrocarbons combinations of C & H Simplest HC molecule = methane 1 carbon bound to 4 H atoms non-polar not soluble in H2O hydrophobic stable very little attraction between molecules a gas at room temperature

Hydrocarbons can grow adding C-C bonds straight line branching ring methane ethane adding C-C bonds straight line ethane hexane branching isohexane ring cyclohexane hexane isohexane cyclohexane

Diversity of organic molecules

Isomers Molecules with same molecular formula but different structures different chemical properties Same formula but different structurally & therefore different functionally. Molecular shape determines biological properties. Ex. Isomers may be ineffective as medicines

Structural isomers Molecules differ in structural arrangement of atoms

Geometric isomers Molecules differ in arrangement around C=C double bond same covalent partnerships

Enantiomer (stereo) isomers Molecules which are mirror images of each other C bonded to 4 different atoms or groups assymetric left-handed & right-handed versions “L” versions are biologically active

Form affects function Structural differences create important functional significance amino acid alanine L-alanine used in proteins but not D-alanine medicines L-version active but not D-version sometimes with tragic results…

Form affects function Thalidomide prescribed to pregnant women in 50’s & 60’s reduced morning sickness, but… stereoisomer caused severe birth defects

Diversity of molecules Substitute other atoms or groups around the C ethane vs. ethanol H replaced by an hydroxyl group (–OH) nonpolar vs. polar gas vs. liquid ethane ethanol

Functional groups Components of organic molecules that are involved in chemical reactions give organic molecules distinctive properties ex: male & female hormones…

Viva la difference! Basic structure of male & female hormones is identical identical C skeleton attachment of different functional groups interact with different targets in the body For example the male and female hormones, testosterone and estradiol, differ from each other only by the attachment of different functional groups to an identical carbon skeleton.

Types of functional groups 6 functional groups most important to chemistry of life: (p.25) hydroxyl u amino carbonyl u sulfhydryl carboxyl u phosphate Affect reactivity hydrophilic increase solubility in water

Hydroxyl –OH (do not confuse this with (OH)-!!) organic compounds with OH = alcohols names typically end in -ol ethanol

Carbonyl C=O O double bonded to C if C=O at end molecule = aldelhyde if C=O in middle of molecule = ketone

Carboxyl –COOH C double bonded to O & single bonded to OH group compounds with COOH = acids (e.g., acetic acid) fatty acids amino acids

Amino -NH2 N attached to 2 H compounds with NH2 = amines amino acids NH2 acts as base ammonia picks up H+ from solution

Sulfhydryl –SH S bonded to H compounds with SH = thiols SH groups stabilize the structure of proteins

Phosphate –PO4 P bound to 4 O connects to C through an O PO4 are anions with 2 negative charges function of PO4 is to transfer energy between organic molecules (ATP)

Why study Functional Groups? These are the building blocks for biological molecules

HOMEWORK Read and make notes 1.1 p. 17 #1-2, 4-7, 9, 11

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 Aka 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 This process releases energy 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

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

Sugars All monosaccharides can be distinguished by the carbonyl group they possess (aldehyde or ketone) along with the # of C in the backbone 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

Sugar Structure cont’d When glucose becomes aqueous, there is a 50% chance that the –OH group at C1 will end up below the plane of the ring. If so, it is called α-glucose. If the –OH group at C1 ends up above the plane of the ring, then it becomes β-glucose.

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

Complex Sugars All sugars are made up of monosaccharides held together by glycosidic linkages. Glycosidic linkages are the covalent bonds that hold 2 monosaccharides together and are formed by condensation reactions in which the H atom of the hydroxyl group comes from one sugar and the –OH group comes from the hydroxyl group of the other.

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 = structural support cellulose (plants) chitin (arthropods & fungi) Humans and other organisms use plants’ stockpile of energy as a food source for themselves. 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

Cow can digest cellulose well; no need to eat supplemental sugars. Have symbiotic bacteria that produce enzymes. Gorilla can’t digest cellulose well; must supplement with sugar source, like fruit

Cellulose Most abundant organic compound on Earth (polymer of β-glucose) Used by plants to create the cell wall Humans are not able to break the glycosidic linkages in cellulose and therefore we cannot digest it. 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.

Homework Read and make notes 1.2 p.21 #7-9, 11, 12