Nucleic Acids: Structure and Function

Study Notes

Nucleic Acids 1: Deconstructing Nucleic Acids

Nucleic acids are macromolecules.
Polymers are built by linking monomers.
Monomers are small, similar chemical subunits.
DNA encodes genes and is made of deoxyribonucleotides.
RNA is needed for gene expression and is made of ribonucleotides.
The subunits of DNA and RNA are nucleotides.
Nucleotides have three parts: a nitrogenous base, a five-carbon sugar (pentose), and one or more phosphate groups.
DNA uses deoxyribose as its sugar. RNA uses ribose as its sugar.
Purines are two-ring structures. Purines include Adenine (A) and Guanine (G).
Pyrimidines are single-ring structures. Pyrimidines include Cytosine (C), Thymine (T), and Uracil (U).
In RNA, Thymine (T) is replaced by Uracil (U).
Nucleotides are connected by phosphodiester bonds to form a polymer.
The sequence of nucleotides in nucleic acids carries genetic information.
The shape of pyrimidines is planar, and purines are nearly so, allowing stacking.
Purines and pyrimidines are hydrophobic and insoluble in water at a near-neutral pH.
The hydrophobic stacking of their rings parallel is crucial for DNA structure.
In the structure of nucleotides, there are specific chemical properties of functional groups.
The bases in a nucleotide are joined to the sugar via a glycosidic bond; a condensation reaction.
The molecular components of DNA and RNA determine their characteristics.
The function of nucleic acids is related to their structure.
Understanding the properties of nucleic acids helps in their laboratory analysis.
A nucleoside comes from a base and a sugar via a glycosidic bond.
To create a nucleotide, a nucleoside and a phosphate group are joined through a condensation reaction.
The sugar-phosphate backbone is the structural framework of nucleic acids.
A single strand of nucleic acid extends in a 5' to 3' direction.
The complementary strands of DNA are held together by hydrogen bonds between base pairs.
DNA uses A-T and G-C pairing.

Purines

Composed of two fused rings.
Each ring contains two nitrogen (N) atoms.
The structure is bicyclic.
Emil Fischer identified purines as variations of a parent structure with differing functional groups.
Examples: Adenine (A) and Guanine (G).

Pyrimidines

Composed of one ring.
Single-ring structures; monocyclic.
Example: Cytosine (C), Thymine (T), Uracil (U).

Chargaff's Rules

Bases are not present in equal proportions.
The amount of adenine equals the amount of thymine.
The amount of cytosine equals the amount of guanine.
The A-T and G-C ratios vary between different species.

Unusual Nucleotide Bases

Some major DNA bases (e.g. cytosine) have modified forms (e.g. methylcytosine)
These forms play a role in regulating gene expression and protecting genetic information.