Summary Biology Notes: DNA Structure and Replication

DNA STRUCTURE AND REPLICATION

Structure of DNA
● Nucleic acids are macromolecules that exist as polymers called polynucleotides
○ Deoxyribonucleic acid (DNA): pentose sugar - deoxyribose; monomers -
deoxyribonucleotides
○ Ribonucleic acid (DNA): pentose sugar - ribose; monomers - ribonucleotides
● Each polynucleotides is composed of monomers called nucleotides
● Each nucleotide is composed of:
○ A five-carbon sugar (pentose)
○ A nitrogenous base
○ A phosphate group

[Pentose Sugar]
● Five-carbon sugars; occur as ring forms
● In nucleic acids, the 5’ carbon is linked in an ester bond to the phosphate group and the 1’
carbon is linked in a glycosidic bond to the nitrogenous base
● Ribose vs Deoxyribose
○ At 2’ carbon of deoxyribose, hydroxyl group (-OH) is replaced by a hydrogen atom (H)
○ Leads to significant differences in structure and thus function of DNA and RNA
○ Partial negative charge of hydroxyl group in ribose repels negative charge of
phosphate -> prevents RNA chain from coiling in as tight a helix as it does in DNA ->
RNA more susceptible to chemical and enzyme degradation than DNA (less stable)




[Nitrogenous Bases]
● Nitrogen-containing ring structure
● Purines and pyrimidines
○ Purines - 6-membered ring fused to 5-membered ring; Adenine (A) and Guanine (G)
○ Pyrimidines - 6-membered ring; Cytosine (C), Thymine (T) and Uracil (U)
● DNA contains A, G, C and T; RNA contains A, G, C and U
○ Only difference between T and U is the presence of a methyl substituent at C​5​ of T

[Nucleoside]
● Formed via condensation reaction of pentose and nitrogenous base
○ 1’ carbon of pentose​ linked via ​glycosidic bond​ to ​nitrogenous base
○ Ribonucleosides and deoxyribonucleosides



Copyright © 2019 tonyndr