DNA

DNA is used for biological information storage. The DNA backbone is sturdy and reliable, making it an excellent method of storing data safely.

Ploidy is the number of copies of a chromosome contained in a tissue. In humans, somantic cells are diploid (two homologous sets of each chromosome) while gametes (reproductive cells) are haploid (one set of a chromosome). Some organisms contain many sets of chromosomes, such as octoploid strawberries.

Nuclear DNA

Mitochondrial DNA

Mitochondria are the power factories of cells. Some cells can contain over 200 mitochondria, and each mitochondrion contains DNA. This mitochondrial DNA, or mtDNA, is inherited maternally. Nuclear DNA and mtDNA are generally considered to be from separate evolutionary origins. Mitochondria were probably once bacteria eaten by eukaryotic organisms. There is no gene recombination in mtDNA, resulting in the same mtDNA being passed from parents to progeny.

In genomics we often work heavily with the mitochondrial genome. Mitochondrial DNA has a faster mutation rate than nuclear DNA, is short, easy to amplify and sequence, and therefore a very important genome for our lab work.





Genes

RNA

The difference between DNA and RNA is





A DNA strand

DNA strands are made of a sugar-phosphate backbone. The DNA strand is ordered in a 5' → 3' (five prime to three prime) direction, with the number derived from which carbon on the sugar is connected to the chain. The sugar is then connected to a base.

The base sequence is the unique idenfication we use in genomics. The base can be A, C, G or T in DNA. In RNA, the T is replaced by U.

The DNA double helix

DNA strands are arranged with a backbone in the 5' → 3' direction, and their complementary strands are flipped around. This chirality, or handedness, is what gives DNA the double helical structure.

Hydrogen bonding

When a hydrogen atom is connected to an electronegative atom (O, N, F), the electronegative atom will not share the electrons evenly. This leaves hydrogen as an exposed proton, creating a δ+ on the hydrogen and a δ- on the electronegative element. This dipole allows hydrogen bonding as the attractive force between δ+ and δ-.

Hydrogen bonding is strong, but it is not as strong as a covalent bond. In a covalent bond electrons are shared between two atoms. In a hydrogen bond there is only attraction between positive and negative molecular dipoles.

In DNA, hydrogen bonding is used to ensure proper pairing. A, T and U only have two hydrogen bonding sites, and can only pair with each other as A-T (in DNA) or A-U (RNA). C and G have three hydrogen bonding sites so can only make pairs as C-G.

Purines and Pyrimidines
Purines

Adenine, Guanine

Pyrimidines

Cytosine, Thymine, Uracil

Pairing

Purines pair with pyrimidines. This means G & A pair with C, T & U. DNA uses ACGT, RNA uses ACGU.