Name____________________________ Pd___________________ Date_____________________
Mr. Orend
Honors Biology
Nucleic Acids
Nucleic acids are macromolecules containing hydrogen, oxygen, nitrogen, carbon, and phosphorous.
Some nucleotides, including the compound known as adenosine triphosphate (ATP), play important roles
in capturing and transferring chemical energy. Individual nucleotides can be joined by covalent bonds to
form a polynucleotide, or nucleic acid.
The heritable genetic information of an organism is stored in the molecule called deoxyribonucleic acid
(DNA). DNA is a kind of nucleic acid, a polymer built from monomers called nucleotides. Another group of
nucleic acids, called ribonucleic acids (RNAs), also plays a key role in cells. As their names indicate, RNA
contains the sugar ribose and DNA contains the sugar deoxyribose.
Nucleotides are the building blocks (the monomers) of nucleic acid polymers. Only four types of
nucleotides make up DNA. Examine the chemical structure of a single nucleotide in Figure 11-5. Notice
that each nucleotide has three parts:
1. A ring-shaped five-carbon sugar.
2. A phosphate group (a phosphorus atom surrounded by four oxygen atoms)
3. A nitrogenous base (ny TRAW juhn us): a single or double ring of carbon and
nitrogen atoms with functional groups (nitrogenous means "nitrogencontaining")
Just as amino acid monomers combine and form a polypeptide, the nucleotides
of a nucleic acid polymer can combine in many different sequences.
Nitrogenous Bases - The four nucleotides found in DNA differ only in their
nitrogenous bases, called bases for short (Figure 11-6). The bases thymine (T) and cytosine (C) are singlering structures called pyrimidines (py RIM uh deenz). Adenine (A) and guanine (G) are larger, double-ring
structures called purines (PYOOR eenz). The one-letter abbreviations stand for both the
bases alone and for the nucleotides containing them.
Complementary Base Pairs The nucleotide adenine pairs with the nucleotide thymine, and
the nucleotide guanine pairs with the nucleotide cytosine. In the biologist's shorthand, A
pairs with T, and G pairs with C. A is also said to be "complementary" to T, and G is
complementary to C. So, while the sequence of nucleotides along the length of one of the
two DNA strands can vary in countless ways, the bases on the second strand of the double
helix are determined by the sequence of the bases on the first strand. Each base must pair
up with its complementary base. In RNA, there is no thymine, so adenine pairs with uracil
(U).
Questions: Write the answers in complete sentences in your notebook.
1. What are the three parts of a nucleotide?
2. List the four nitrogenous bases found in DNA.
Now complete your summary blue table on nucleic acids