Natural Product Biomolecules - Organic Chemistry Concepts: An EFL Approach - page 163

Proteins have four levels of structural complexity.

Primary structure is the sequence in which the amino acids are connected. n

Secondary structure refers to the way pieces of the peptide structure
are arranged because of intramolecular or intermolecular hydrogen
bonding.

n

Tertiary structure is the overall three-dimensional shape of the protein.
This is the added result of all the secondary structures.

n

Quaternary structure is the result of binding together of several protein
molecules to give large structures which are the proteins in their func-
tional role.

n

Overall, amino acids, peptides, and proteins have important structural and regu-
latory roles in all living cells.

8.5 NUCLEIC ACIDS
The nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA),
are the molecules responsible for carrying the genetic information of a cell.
In the same way that proteins are polymers of amino acids, nucleic acids
are long chain “polymers” of nucleotide building blocks. Each nucleo-
tide is made up of a nucleoside along with phosphoric acid. As shown in
Figure 8.21 , each nucleoside is made up of a simple aldopentose sugar and a
heterocyclic amine base. Base refers to the ability of the nitrogen lone pair to
accept a proton.

FIGURE 8.21
Nucleic acid composition.

Nucleic acids bring together the features of the sugars, phosphate esters, and
amines which we studied earlier. Although nucleic acids seem complex, they
follow much of the same simple functional group chemistry.

Figure 8.22 shows the only two sugars which occur in nucleic acids: β- d -ribose in
RNA and β- d -2-deoxyribose in DNA These sugars differ from each other only in
the presence or absence of the hydroxyl group at C 2 . The naming of the nucleic
acids is based on the names of these sugars.