E. Nucleic acids

1. Nucleic acids are polymers of nucleotides

2. Each nucleotide consists of a phosphate group, a five-carbon (pentose) sugar, and a nitrogenous base (a ring-like structure that contains nitrogen and carbon atoms)

3. Two types of nucleic acid exist

a. Deoxyribonucleic acid (DNA) has a double-helix structure

(1) The double helix of DNA consists of two long chains of nucleotides that twist or spiral around an imaginary axis to form a molecular structure reminiscent of a spiral staircase or ladder

(2) The two vertical members of the helix "ladder" are formed by the alternating sugar and phosphate groups of the nucleotides

(3) The nitrogenous bases of the nucleotides are paired in the interior of the helix

(4) DNA stores genetic information as a code represented by the linear sequence of the four different nitrogenous bases of the nucleotides; the pattern of the nucleotide bases determines, via the genetic code, dif­ferent amino acids in protein synthesis

(5) DNA is a self-replicating molecule that can faithfully ensure its own duplication

(6) It contains deoxyribose sugar (C₅H₁₀O₄), a form of the pentose sugar that contains one less oxygen atom than ribose (C₅H₁₀O₅)

b. Ribonucleic acid (RNA) appears in three forms within cells and is usually a single-stranded molecule containing ribose sugar

(1) Ribosomal RNA (rRNA) is a component of the cellular structure that is responsible for synthesizing polypeptides known as ribosomes

(2) Messenger RNA (mRNA) is a molecule that carries the information to make a specific polypeptide; it is synthesized from DNA and used by the ribosomes to help in the synthesis of polypeptide chains

(3) Transfer RNA (tRNA) is a small RNA molecule which ensures that the proper amino acid is added to a growing peptide chain during protein synthesis

4. Each nucleotide of DNA or RNA contains two types of nitrogenous bases

a. A pyrimidine base is a single-ring structure

(1) The three pyrimidines are thymine, cytosine, and uracil

(2) DNA contains thymine and cytosine; RNA contains cytosine and uracil

b. A purine base is a double-ring structure

(1) The two purines are adenine and guanine

(2) DNA and RNA contain both types of purines

5. Nucleotides other than those used to synthesize nucleic acids include energy carrier molecules, such as adenosine triphosphate (ATP), which carry energy from place to place within a cell, and intracellular messengers, such as cyclic adenosine monophosphate (AMP), which coordinate chemical reactions within cells

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