Although Cells Are 70-95% Water, the Rest Consists Mostly of Carbon-Based Compounds

Chapter 4: Carbon

Fall 2012

Carbon

•  Although cells are 70-95% water, the rest consists mostly of carbon-based compounds.

•  Carbon forms the backbone of proteins, fats, carbohydrates, and nucleic acids

We all eat at the SPONCH CaFé (but not in that order…HOCNCaPSFe is just too hard to pronounce!!)

•  Percentages don’t vary much from one organism to another.

•  However, because of carbon’s versatility, these few elements can be combined to build an inexhaustible variety of organic molecules.

Organic Chemistry

•  Organic chemistry is the study of carbon containing molecules

•  This includes carbon-containing molecules that are derived from nonliving sources.

–  Organic compounds can range from simple molecules, such as CO2 or CH4, to complex molecules, like proteins.

A carbon atom

•  Carbon’s atomic number is 6. This means it has 4 valance electrons.

•  It has little tendency to form ionic bonds by loosing or gaining 4 electrons.

•  Instead, it usually completes its valence shell by sharing electrons with other atoms in four covalent bonds.

•  This tetravalence by carbon makes large, complex molecules possible.

Organic molecule: Building Code

•  Commit to memory the valances for the 4 major organic elements:

•  Carbon = 4, Nitrogen = 3; Oxygen = 2, Hydrogen = 1;

•  Also remember that carbon can bond to itself and can form double bonds to nitrogen, oxygen and carbon atoms

•  These give you the basic rules for how organic bonds are made.

Examples

•  Carbon Dioxide – CO2

•  Urea – CO(NH2)2

•  Hydrocarbons

–  Chains of various length (Ethane vs. Propane)

–  Location of Double Bonds (1-Butene vs. 2-Butene)

–  Branching (Butane vs. 2-methylpropane)

–  Rings (cyclohexane vs. benzene)

Significance of Hydrocarbons

•  Hydrocarbons are the major component of petroleum

•  Regions of molecules in our cells consist of hydrocarbons

•  Hydrocarbons are nonpolar and therefore, hydrophobic

•  The bonds in a hydrocarbon store lots of energy that is released upon burning.

Isomers

•  An isomer is a compound that has the same numbers of atoms of the same elements but a different structure and different properties

•  3 kinds of isomers:

–  Structural

–  Geometric

–  Enantimers

Structural Isomers

•  Differ in the covalent arrangement.

•  Number of isomers increases as you increase the size of the carbon skeletons

•  3 isomers of C5H12

•  18 isomers of C8H18

•  366,319 isomers of C20H42

Geometric Isomers

•  Isomers that have the same sequence of atoms but differ in the spatial arrangement of atoms due to the presence of a double bond.

Enantiomers

•  Molecules that are a mirror image of each other.

•  Middle carbon is asymmetrical (attached to 4 different atoms or groups of atoms)

•  Designated L and D for left (levo) and right (dextro)

•  They can’t be superimposed on each other

Functional Groups

•  Functional groups are organic molecules that attach to hydrocarbons and are commonly involved in chemical reactions.

•  Think of it as a generic “person” who can take on different identities with different hats.

•  Each functional group behaves consistently from one organic molecule to the next.

•  There are SIX functional groups

Hydroxyl (-OH)

•  Polar covalent bond between oxygen and hydrogen and between oxygen and the rest of the molecule. Makes this group very soluble in water

•  Molecules with a hydroxyl group are alcohols and their names end in –OH

Carbonyl (-CO)

•  Oxygen double bonded to the carbon chain.

•  In the middle of the molecule it‘s called a ketone

•  On the end of the molecule, it’s called an aldehyde

Carboxyl (-COOH)

•  Oxygen is double bonded to a carbon that is also bonded to a hydroxyl group.

•  Acids because the H on the OH will rapidly dissociate.

Amino (NH2)

•  Nitrogen bonded to two hydrogen atoms and to the carbon skeleton

•  Called Amines

•  Amino acids have both and amino group and a carboxyl group

Sulfhydryl (-SH)

•  Sulfur bonded to hydrogen and also bonded to the carbon skeleton

•  Called Thiols

•  Two sulfhydryl can interact to stabilize proteins; this structure is called a disulfide bridge

Phosphate -OPO32-

•  Oxygen bonded to the carbon skeleton and phosphate.

•  Phosphate also bonded to 3 more oxygens

•  Makes whole molecule an anion because it so rapidly loses H ions leaving a negative charge behind.