AP Biology Notes Outline Chapter 4: Carbon and the Molecular Diversity of Life

CONCEPT 1: The Importance of Carbon

Although a cell is composed of 70-95% water, the rest consists mostly of carbon-based compounds.Hydrogen (H), Oxygen (O), Nitrogen (N), Sulfur (S), and Phosphorus (P) are other common ingredients comprise biological molecules.

Compounds containing carbon are said to be organic. Organic chemistry is the branch of science that specializes in the study of carbon compounds.

Valence is the number of covalent bonds an atom will usually form. Valence is usually equal to the number of electrons needed to complete the outermost shell. The electron configuration of carbon gives it covalent compatibility with many different elements. A covalent-bonding capacity of four contributes to carbon’s ability to form diverse molecules. Carbon can bond to a variety of atoms and carbon can also bond to other carbons, forming the carbon skeletons of organic compounds.

The carbon skeletons of organic molecules vary in length and shape and have bonding sites for atoms of other elements.

AP Biology Notes Outline Chapter 4: Carbon and the Molecular Diversity of Life

CONCPET 2: Hydrocarbons

Hydrocarbons consist only of carbon and hydrogen. Many organic compounds have regions that consist only of these. Many are insoluble in water because the C-H bond is nonpolar and the water molecules are polar.

Fats have long hydrocarbon tails that are nonpolar attached to a polar head. These hydrocarbon tails store a relatively large amount of energy.

a. Triglycerides are fat molecules consists of a headpiece and 3 hydrocarbon tails – the tails store energy and account for the hydrophobic behavior of fats.

b. Mammalian adipose cells stockpile fat molecules as a fuel reserve.

CONCPET 3: Isomers

Isomers are compounds that have the same molecular formula, but different structures - and, different properties as a result. There are 3 types of isomers important in Biology:

1. Structural isomers2. Geometric isomers3. Enantiomers

Structural Isomers differ in the covalent arrangement of their atoms. They may also differ in the location of double bonds. As the carbon skeleton increases in size, the number of possible isomers increases tremendously. Structural isomers often differ in covalent partners & possibly location of double bonds: (i.e. butane and isobutane).

Geometric Isomers have the same covalent partnerships, but differ in their spatial arrangements. This phenomenon arises from the inflexibility of double bonds – will not allow the atoms they join to rotate freely about the bond axis (unlike single bonds). Geometric isomers often differ in arrangement about a double bond. This slight difference in shape can dramatically affect the biological activity of the molecules.

AP Biology Notes Outline Chapter 4: Carbon and the Molecular Diversity of Life

Enantiomers are molecules that are mirror images of each other. Usually, these “right-handed” and “left-handed” versions of the same molecule allow for one to be biologically active and the other inactive (i.e. thalidomide).

Enantiomers often differ in spatial arrangement around an asymmetric carbon. This results in molecules that are mirror images, like left and right hands.

Two enantiomers of a drug may not be equally effective (and in some cases, produce harmful effects). Thalidomide was prescribed for pregnant women in the late 50’s – a drug that was a mixture of two enantiomers.

• one enantiomer reduced morning sickness• the other caused severe birth defects

CONCEPT 4: Functional Groups

Functional groups are the components of organic molecules that are usually involved in chemical reactions. Each group behaves consistently from one organic molecule to another. The number and arrangement of functional groups help give each molecule its unique properties.

Two molecules differ mainly in the attachment of functional groups to a common carbon skeleton. These subtle variations in molecular architecture influence the development of the anatomical and physiological differences between female & male vertebrates. Sexuality has a biological basis in variations of molecular architecture!

AP Biology Notes Outline Chapter 4: Carbon and the Molecular Diversity of Life

AP Biology Notes Outline Chapter 4: Carbon and the Molecular Diversity of Life

CONCEPT 4: ATP: An Important Source of Energy for Cellular ProcessesAdenosine triphosphate, or ATP, is the primary energy-transferring molecule in the cell. ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups. The structure also includes as ribose sugar, as shown below:

Notice in the above figure that the phosphates are NEGATIVELY charged...this configuration makes the molecule highly unstable.

Where three phosphate groups are present in a series, as in ATP, one phosphate may split off as an inorganic phosphate ion (abbreviated as Pi). This process is known as the HYDROLYSIS of ATP.

Losing one phosphate, ATP becomes ADP (adenosine diphosphate). The reaction releases energy that can be used by the cell.