Carbon & the Molecular Diversity of Life

Most biologically important molecules are carbon-based (exception: water)

Diversity arises from the ability of C to form large, complex & diverse molecules by bonding to itself & other elements: H, O, N, S, P

Organic Chemistry = study of carbon compounds Vitalsim

Belief in a life force outside the jurisdiction of chemical/physical laws

19th C. organic chemistry built on vitalism because could not synthesize organic compounds

Believed only living organisms could produce organic compounds

Mechanism

Belief that all natural phenomenon are governed by physical & chemical laws

Gained prominence as organic molecules synthesized from inorganic

Wohler =Urea (1828); Kolbe = acetic acid; Miller (1953) = primordial compounds

Carbon Atom

Atomic # = 6

4 valence electrons

Ionic bonds unlikely

4 covalent bonds

Tetravalent electron configuration

Makes large molecules possible

Gives carbon compatibility with other elements (H, O, N )

Determines 3-D shape, which effects function

Variation = Diversity

C skeletons vary in

--Length

--Shape (straight, chain, ring

--# & location of double bonds

Other elements covalently bonded at available sites

Hydrocarbons

--Contain only C and H

--Major component of fossil fuels

--Various lengths & shapes

--Fats contain hydrocarbon chains

--Are hydrophobic because C-C and C-H are non-polar

Isomers

Same molecular formula but different structural formula

Results in different properties

Three types:

--Structural

--Geometric

--Enantiomers

Structural

--differ in covalent arrangement of atoms

--# of possible isomers increases with size

--Location of double bonds may differ

Geometric

--Isomers share same covalent partnerships but differ in spatial arrangements

--Arise because Double bonds do not allow free rotation

--Subtle differences affect biological activity

--Enantiomers

--Mirror images

Asymmetric C = 4 groups bond to same C = 2 different spatial arrangements of those 4 groups possible

1 form active; other not

Functional Groups

--Contribute to molecular diversity

--Have specific chemical & physical properties

--Region of chemical activity

--Behave consistently

--Determine unique chemical properties, depending on # and arrangement

Hydroxyl Group

--Functional group consisting of H atom bonded to O atom, bonded to C (-OH)

--Is polar. O-H bond polar covalent

--Makes the molecule water soluble

--Organic compounds with OH groups are alcohols

Carbonyl Group

--Consists of a C atom double bonded to O (-CO)

--Also polar; water soluble

--Found in sugars

--If at end, aldehyde

--If carbonyl is at end off C skeleton = ketone

Carboxyl Group

--Consists of a C atom which is both double bonded to an O and single bonded to the O of a hydroxyl group (-COOH)

--Polar, water soluble; acidic

--Carboxylic acids(Acetic acid to acetate ion + H+)

Amino Group

--Consists of a N atom bondfed to 2 H and to C skeleton (-NH2)

--Polar, water soluble, weak base

--Unshared pair of electrons on the N can accept a proton, resulting in +1amines

Sulfhydryl Group

--Consists of an atom of S bonded to an atom of H (-SH)

--Stabilize structure of proteins (disulfide bridges) thiols

Phosphate Group

--Group is the dissociated form of phosphoric acid (H3PO4)

--Loss of 2 protons by dissociation leaves a - charge

--Acidic, polar, water soluble

--Important in cellular energy storage & transfer

Methyl Group

--Consists of 3 H bonded to C (-CH3)

--Nonpolar, hydrophobic

--Important in tertiary structure of proteins (including membrane proteins)