Properties of Nucleic Acids - Genetics

Uracil is a nucleic acid found in RNA but not DNA. Therefore, if a question has uracil as one of the nucleic acids in the sequence, you know that you are dealing with a piece of RNA. RNA is genetic material that has been transcribed from a piece of DNA.

The 5' to 3' linkages of DNA residues are via phosphodiester bonds, which are a type of covalent bond.

The following are the major steps in gene product modification:

1. Transcription of DNA into mRNA (primary transcript)

2. Pre-mRNA processes (mature transcript)

3. Translation of mRNA by tRNA (proteins)

4. Post-translational processing (modified protein)

A nucleotide is the building block of nucleic acids, such as DNA & RNA. They contain a phosphate group, 5-carbon sugar & nitrogen-containing base all covalently bound together.

For DNA base-pairings, A-T must be paired up (2 hydrogen bonds) and G-C must be paired up (3 hydrogen bonds). For RNA base-pairings, A-U pair up instead of A-T.

Pyrimidine bases include cytosine, thymine, and uracil (RNA), and are monocyclic. Purine bases include adenine and guanine, and are bicylic with two rings in the molecular structure.

According to Chargoff's rules, we know that the ratios of Adenine:Thymine and Guanine: Cytosine will be approximately 1:1. Once you know that the percentage of Adenine is 18%, you can multiply by two to find the total percentage of Thymine and Adenine (36%), then, you can subtract that number from 100% to find the percentage of Cytosine and Guanine - 64% (because the total percentage has to equal 100%), finally you can divide it in half to get the percentage of Guanine bases (32%).

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.

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.

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.

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.

Austrian chemist Erwin Chargaff discovered that the amount of cytosine was equal to the amount of guanine in the cell, and the amount of adenine was equal to the amount of thymine in the cell. This discovery was important in determining that cytosine always pairs with guanine and that adenine always pairs with thymine.

In RNA, uracil pairs with adenine and cytosine pairs with guanine, whereas in DNA, thymine pairs with adenine and cytosine pairs with guanine. Uracil is unique to RNA and thymine is unique to DNA.