The Chemicals of Life 1.2

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

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 H2O– 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

cyclohexaneisohexane

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 withtragic 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

ethanolethane

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 amino– carbonyl sulfhydryl– carboxyl 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

…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” 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

Carbohydrates

Carbohydrates• Carbohydrates are composed of C, H, O

carbo - hydr - ate

CH2O (empirical formula)

(CH2O)x C6H12O6

• Function:– energy energy storage– raw materials 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

CC

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

monosaccharides disaccharide

|maltose

Building sugars

• Dehydration synthesis

|fructose

|glucose

glycosidic linkage

monosaccharides disaccharide

|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

Cowcan digest cellulose well; no need to eat supplemental sugars. Have symbiotic bacteria that produce enzymes.

Gorillacan’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