Chapter 4: Carbon

Carbon Overview: Carbon—The Backbone of Biological Molecules All living organisms are made up of chemicals based mostly on the element carbon Organic chemistry is the study of carbon compounds

The Formation of Bonds with Carbon Carbon has four valence electrons This allows it to form four covalent bonds with a variety of atoms

The bonding versatility of carbon Allows it to form many diverse molecules, including carbon skeletons (a) Methane (b) Ethane (c) Ethene (ethylene) Molecular Formula Structural Formula Ball-and-Stick Model Space-Filling Model H C CH4 C2H6 C2H4 Name and Comments

Common Bonding Partners of Carbon The electron configuration of carbon Gives it covalent compatibility with many different elements H O N C Hydrogen (valence = 1) Oxygen (valence = 2) Nitrogen (valence = 3) Carbon (valence = 4)

Which of the structures in this figure is an impossible covalently bonded molecule? Answer: c Source: Barstow - Test Bank for Biology, Sixth Edition, Question #28

Molecular Diversity Arising from Carbon Skeleton Variation Carbon chains Form the skeletons of most organic molecules Vary in length and shape H C (a) Length (b) Branching (c) Double bonds (d) Rings Ethane Propane Butane 2-methylpropane (commonly called isobutane) 1-Butene 2-Butene Cyclohexane Benzene

Hydrocarbons Hydrocarbons Are molecules consisting of only carbon and hydrogen The bonds between the C and H atoms are non-polar covalent This makes hydrocarbons hydrophobic

(b) Mammalian adipose cells Hydrocarbons Hydrocarbons Are found in many of a cell’s organic molecules (a) A fat molecule (b) Mammalian adipose cells 100 µm Fat droplets (stained red)

Isomers Isomers Are molecules with the same molecular formula but different structures and properties

(a) Structural isomers Three types of isomers are Structural Geometric Enantiomers H CO2H CH3 NH2 C X (a) Structural isomers (b) Geometric isomers (c) Enantiomers

Why are Enantiomeric isomers important? Enzymes distinguish between enantiomers! H CO2H CH3 NH2 C X (a) Structural isomers (b) Geometric isomers (c) Enantiomers Enzyme activity = 100 % Enzyme activity = 0 %

Structure and Function Subtle changes in structure can dramatically affect the molecule’s function

The Functional Groups Functional groups Are the chemically reactive groups of atoms within an organic molecule They behave consistently and characteristically, giving unique properties to the molecules possessing them.

Six functional groups are important in the chemistry of life Hydroxyl Carbonyl Carboxyl Amino Sulfhydryl Phosphate

Functional Groups  OH FUNCTIONAL GROUP STRUCTURE (may be written HO ) HYDROXYL CARBONYL CARBOXYL OH In a hydroxyl group (—OH), a hydrogen atom is bonded to an oxygen atom, which in turn is bonded to the carbon skeleton of the organic molecule. (Do not confuse this functional group with the hydroxide ion, OH–.) When an oxygen atom is double-bonded to a carbon atom that is also bonded to a hydroxyl group, the entire assembly of atoms is called a carboxyl group (—COOH). C O The carbonyl group ( CO) consists of a carbon atom joined to an oxygen atom by a double bond. 

Acetone, the simplest ketone Functional Groups HYDROXYL CARBONYL CARBOXYL Acetic acid, which gives vinegar its sour tatste NAME OF COMPOUNDS Alcohols (their specific names usually end in -ol) Ketones if the carbonyl group is within a carbon skeleton Aldehydes if the carbonyl group is at the end of the carbon skeleton Carboxylic acids, or organic acids EXAMPLE Propanal, an aldehyde Acetone, the simplest ketone Ethanol, the alcohol present in alcoholic beverages H C OH O

Functional Groups The amino group (—NH2) consists of a nitrogen atom bonded to two hydrogen atoms and to the carbon skeleton. AMINO SULFHYDRYL PHOSPHATE (may be written HS ) The sulfhydryl group consists of a sulfur atom bonded to an atom of hydrogen; resembles a hydroxyl group in shape. In a phosphate group, a phosphorus atom is bonded to four oxygen atoms; one oxygen is bonded to the carbon skeleton; two oxygens carry negative charges; abbreviated P . N H SH O P OH

Functional Groups Ethanethiol Glycine Glycerol phosphate AMINO SULFHYDRYL PHOSPHATE Because it also has a carboxyl group, glycine is both an amine and a carboxylic acid; compounds with both groups are called amino acids. Glycine Ethanethiol Glycerol phosphate O C HO H H N C SH OH O P O

Effect of Different Functional Groups Functional groups give organic molecules distinctive chemical properties CH3 OH HO O Estradiol Testosterone Female lion Male lion

Key Points of Chapter 4 Organic chemistry is the study of carbon compounds Carbon atoms can form diverse molecules by bonding to 4 other atoms Functional groups are the parts of molecules involved in chemical reactions and behave chemically in expected manners

Chapter 4 Essay Question Discuss the biological importance of each of the following organic compounds in relation to cellular structure and function in plants and animals. a. Carbohydrates b. Proteins c. Lipids d. Nucleic acids