Central Dogma

Deoxyribonucleic acid (DNA) is the hereditary material of all living organisms, including humans. The information of the DNA is copied to ribonucleic acid (RNA), in a process called转录. The nucleotide sequence in RNA will be translated to protein in a process calledtranslation. The flow of information from DNA to RNA, and RNA to protein is known as the central dogma.

Bases

DNA stores information through a code made up of four chemical bases: A (adenine), T (thymine), C (cytosine), and G (guanine), and it is the order (or sequence) of these four bases that determines the information provided by DNA. RNA also stores information in four bases, but thymine bases are replaced by uracil. Each base pairs with another complementary base to form base pairs, which allow the DNA to maintain its double helical structure. The information is used as instructions for building and maintaining all the cells of an organism. The human genome consists of approximately 3.2 billion base pairs.

Figure 1:DNA and mRNA synthesis proceeds in 5' to 3' direction. The 5' and 3', or five prime and three prime, refer to the number of the carbon molecules in the sugar backbone. The 5' carbon has a phosphate group and the 3' carbon has a hydroxyl group.

Structure

DNA is composed of two strands running in opposite directions that are twisted together, also called the double helix. The strands are composed of nucleotides and deoxyribose sugars. A phosphodiester link connects the deoxyribose sugars with each other, and the hydrogen bonds between phosphates cause the DNA strand to twist. The two strands are bound with weak hydrogen bonds between the complementary nucleotides. The nitrogenous bases are “inside” like rungs on a ladder. Adenine binds with thymine and cytosine binds with guanine.

On the contrary, RNA exists as a single strand. Complementary pairing can occur and result in various shapes of RNA.

DNA and RNA are constructed from different types of sugars. The only difference between these two sugars is that deoxyribose lacks an oxygen atom on the second carbon in the ring; hence the name deoxyribose.

The following table summarizes the difference between RNA and DNA