The Chemicals of Life 1.2

Why study Carbon? All living things are made of cells Cells –~72% H 2 O –~3% salts (Na, Cl, K…) –~25% carbon compounds –carbohydrates –lipids –proteins –nucleic acids

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

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 H 2 O –hydrophobic –stable –very little attraction between molecules –a gas at room temperature

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

Diversity of organic molecules

Isomers Molecules with same molecular formula but different structures –different chemical properties

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 ethanol ethane

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

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 -NH 2 –N attached to 2 H compounds with NH 2 = amines –amino acids NH 2 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 –PO 4 –P bound to 4 O connects to C through an O PO 4 are anions with 2 negative charges function of PO 4 is to transfer energy between organic molecules (ATP)

Why study Functional Groups? These are the building blocks for biological molecules …and that comes next! p.27 Q 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 chain of repeating smaller units –polymers –monomers = repeated small units –covalent bonds

How to build a polymer Condensation reaction –Aka dehydration synthesis –joins monomers by “taking” H 2 O out 1 monomer provides OH the other monomer provides H together these form H 2 O –requires energy & enzymes

How to break down a polymer Hydrolysis –use H 2 O to break apart monomers reverse of condensation reaction H 2 O 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

Carbohydrates

Carbohydrates are composed of C, H, O carbo - hydr - ate CH 2 O (empirical formula) (CH 2 O) x  C 6 H 12 O 6 Function: –energy u energy storage –raw materials u structural materials Monomer: simple sugars (e.g., glucose) ex: sugars & starches

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 ketone aldehyde 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 CC C C C 1' 2'3' 4' 5' 6' O

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 | glucose | glucose glycosidic linkage monosaccharidesdisaccharide | maltose

Building sugars Dehydration synthesis | fructose | glucose glycosidic linkage monosaccharidesdisaccharide | sucrose structural isomers

Polysaccharides Polymers of sugars –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.

Branched vs linear polysaccharides

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

Digesting starch vs. cellulose

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.

Practice p.34 Q 2-8, 10