Nucleic Acids

Nucleic Acids

1. Phosphate
2. Sugar
3. Base

Difference Between RNA and DNA

• The nucleotide shown above would be found in DNA.
• In RNA, there are two -OH groups attached to the sugar molecule while in DNA there is only one (this is why it is called "deoxyribonucleic acid", because one oxygen has been removed).

Diversity of Nucleotides

• There are five possible nitrogenous bases that may be attached to a nucleotide.
• These nitrogenous bases can be divided into two groups: purines and pyrimidines:
• Purines have a two-ring structure, while pyrimidines are composed of just one ring.
• Adenine, Guanine, Cytosine, and Thymine can be found in DNA (A,G,C,T).
• Adenine, Guanine, Cytosine, and Uracil can be found in RNA (A,G,C,U).

• Nucleotides are joined together to form long chains through a dehydration / condensation reaction to form a phosphodiester bond between the phosphate group of one nucleotide and the hydroxyl group on the sugar of another nucleotide.
• When joined together, one end of the chain will have a free phosphate group, while the other end of the chain will have a free carboxyl group.
• The end with the free phosphate group is called the 5' end, because the phosphate is attached to the 5' carbon of the sugar.
• The end with the free carboxyl group is called the 3' end, because the carboxyl is attached to the 3' carbon of the sugar.

The DNA Double Helix

• The two strands are arranged to have their sugar and phosphate groups along the outside, with their nitrogenous bases pointing inward.
• The nitrogenous bases of the two strands form hydrogen bonds with each other, holding the two strands together.
• The strands will be arranged in a complementary and antiparallel fashion.
• Complimentary means that A will always pair up with T, and C will always pair up with G. In RNA, T is not present so A pairs up with U instead.
• Two hydrogen bonds form between A and T base pairs, and three hydrogen bonds form between C and G base pairs.
• The strands are antiparallel, meaning that one strand will be running from the 5' end to the 3' end, while the strand it is paired up with will be running in the opposite direction.