Last modified on 25 November 2013, at 18:51

AP Biology/DNA


DNA (Deoxyribonucleic acid) is what contains all of the information for life on earth. Every living thing including a bacteria cell to a killer whale has its own unique genetic code, which can be found within its DNA. This information has the ability to replicate itself ensuring that the species can continue by producing offspring exactly identical to its own. This is known as reproduction and is vital for life, as the life span of any being is limited.


Base pair GC.svg
Base pair AT.svg
At top, a GC base pair with three hydrogen bonds. At the bottom, AT base pair with two hydrogen bonds. Hydrogen bonds are shown as dashed lines.

DNA is a double-helix that is made up of three main components. The monosaccharide Deoxyribose acts as a base, and this is connected to a nitrogenous base, and also to a phosphate group - collectively these are known as 'Nucleotides' and linked together cause a chain which, when linked to another chain of nucleotide becomes DNA. There are four types of nitrogenous bases: adenine, thymine, cytosine, and guanine. Adenine and guanine are purines, meaning that they have a double-ring base. While thymine and cytosine are pyrimidines, meaning that they have a single-ring base. Adenine and thymine always bind together, while cytosine and guanine always bind together. This is called complimentarity.

DNA ReplicationEdit

DNA replication occurs during interphase in a cell cycle. It is essential for cell division as a way to pass on genetic information to the next "generation" of cells. First, the DNA double-helix is separated into two strands using the enzyme helicase, which unwinds the DNA double-helix to form a y-shaped replication fork. Binding proteins that are single-stranded prevent the newly separated DNA strands from recombining.