Every nucleic acid is made up of 3 parts — a pentose (5 membered ring) sugar, a phosphate group and a nitrogenous base. 

A hexose sugar has a six membered ring. Ribose and deoxyribose are types of sugars found in nucleic acids, but are only found in RNA and DNA respectively.

While DNA is usually found double stranded and RNA is often found single stranded, RNA can also be found in double stranded forms, notably in viruses. 

Adenine and Guanine are purines and consist of two connected nitrogenous rings. Cytosine, Uracil, And Thymine are pyrimidines and consist of one nitrogenous rings.

One can remember this by remembering that stones had to be CUT in order to build the PYRAMIDs.

The aromatic nitrogenous bases absorb UV radiation, which allow nucleic acids to be detected by UV absorbance.

Nucleosides have only a nitrogenous base attached to the sugar. Nucleotides have a phosphate group and a nitrogenous base attached to the sugar. An easy way to remember this is that nucleoSides have a single group attached to the sugar, and nucleoTides have two groups attached to the sugar.

Using Chargoff's rules, one can calculate that Virus A has 64% C-G pairs in its genome and Virus B has 50% C-G base pairs in its genome. Since C-G pairs have an additional hydrogen bond, they are more stable than A-G pairs, so more energy will be required to separate the strands and "melt" the DNA. Since the two genomes are the same length, the stacking effects will be the same, so the deciding factor will be base pair composition, and Virus A's genome will have a higher melting temperature.

Of the major types of macromolecules — lipids, proteins, nucleic acids, and carbohydrates — only nucleic acids contain phosphorous.

Base pairs connect across the center of the double Helix using multiple hydrogen bonds. A-T pairs use 2 hydrogen bonds and C-G pairs use 3 hydrogen bonds. 

Phosphodiester bonds do connect nucleotides, but they connect them along the backbone of DNA and do not connect the base pairs. Disulfide bridges connect sulfur containing R groups in proteins. Covalent bonds is a large category of chemical bonds, but base paired nucleotides are connected through intermolecular forces (H-Bonds) rather than bona fide chemical bonds. 

The 5' end of a DNA strand is defined by the presence of the 5' carbon on the deoxyribose sugar towards that end. At the 5' carbon, there is a phosphate group which allows it to be added to the growing nucleotide chain. 

A deoxyribose sugar is a major component of DNA, but it is not the functional group located at the 5' end of the DNA strand. The nitrogenous bases are attached to the 1' carbon. The poly A tail is a post transcriptional modification of mRNA.

Other than the sites of hydrogen bonding, the nitrogenous rings are hydrophobic in nature. This property leads them to stick toward the center of the helix and away from the polar solvents around them. Once they are correctly base paired, their hydrophilic sites are mitigated by the hydrogen bonding leading to increased stability.