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Nucleic Acids
Nucleic acids are what constitutes our genetic code. The monomers of nucleic acids, which includes both DNA and RNA, are called nucleotides. Nucleotides have three key ingredients:
- Phosphate
- Sugar
- Base
Difference Between RNA and DNA
DNA and RNA nucleotides differ in the structure of the sugar group.
- 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).
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The DNA Double Helix
Two long strands of DNA come together to for 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.
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Example: Complimentary Base Pairing
Below is an image of one strand of a DNA double helix. Fill in the other DNA strand using proper complimentary base pairing. Make sure to draw the correct single or double ring structure of the nucleotide, and indicate with dashed lines the number of hydrogen bonds between each of the nucleotides.
Practice: Making Nucleic Acids
Which of the following combinations could be linked together to form a nucleotide?
Practice: Nucleic Acid Building Block
Which macromolecule does the molecule below belong to?
Practice: Complimentary Base Pairing
Fill in the blanks describing the nitrogenous base in a DNA molecule.
Adenine base pairs with .
Guanine base pairs with .
Thymine contains a ring structure.
Guanine contains a ring structure.
Practice: Nucleotide Base Pairing
Which of the following is the correct 5' to 3' sequence of the complimentary strand to: 5'-AGGTCTGATTCGTA-3' ?