Structure and replication of DNA

Understanding the structure of nucleic acids allows an understanding of their role in the storage of genetic information and how that information is used in the synthesis of proteins.

1. Describe the structure of nucleotides, including the phosphorylated nucleotide ATP (structural formulae are not required)

• The basic structure of a nucleotide is composed of a pentose (5-carbon) sugar, a nitrogenous base (purine or pyrimidine) and a phosphate group
• The nucleotide in deoxyribose nucleic acid (DNA) has a pentose sugar called a deoxyribose which lacks an oxygen atom, hence the name 'deoxy-'
• The nitrogenous base in a DNA can be either adenine (A), thymine (T), guanine (G) or cytosine (C) and is always bonded to the 1st carbon
• The phosphate group is attached to the 5th carbon
• The nucleotide in ribonucleic acid (RNA) has a pentose sugar called ribose and its structure is similar to the deoxyribose, except for the fact that it has the extra oxygen atom that DNA does not have
• The nitrogenous base in an RNA is bonded to the 1st carbon and can either be uracil (U), thymine (T), guanine (G) or cytosine (C)
• The phosphate group in an RNA is attached to the 5th carbon
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• The structure of the phosphorylated nucleotide ATP consists of a the pentose sugar ribose, the nitrogenous base adenine (A) at the first carbon and either one, two or three phosphate groups attached at the 5th carbon
• If there is only one phosphate group, it is called adenosine monophosphate (AMP)
• If there is two, adenosine diphosphate (ADP)
• And if there is three, adenosine triphosphate (ATP)

2. Describe the structure of RNA and DNA and explain the importance of base pairing and the different hydrogen bonding between bases (include reference to adenine and guanine as purines and to cytosine, thymine and uracil as pyrimidines. Structural formulae for bases are not required but the recognition that purines have a double ring structure and pyrimidines have a single ring structure should be included)

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• A DNA is a polynucleotide, meaning that its monomers are nucleotides
• A nucleotide…