RNA + Knowledge

From gene to gene product: Gene expression

Whenever the cell requires a certain protein, the gene for this protein is transcribed into a messenger molecule, the mRNA (messenger ribonucleic acid). This copying process - called transcription - requires a specific enzyme, the RNA polymerase. The mature mRNA is then translated into the protein by a ribosome. This process is termed translation. This flow of genetic information from DNA to RNA to protein takes place in all living organisms and is therefore (almost) universal. This sequence of events is therefore also known as the "central dogma of molecular biology".

During cell division, the DNA is duplicated. After division, both cells contain the complete genetic information. This process is known as DNA replication.

In animals, humans and plants, transcription (production of RNA) takes place in the cell nucleus, while translation (protein synthesis) takes place outside the cell nucleus in the cytoplasm. Bacteria do not have a cell nucleus; their circular DNA is located in the cytoplasm. Therefore, in bacteria, both processes take place in the cytoplasm.

This figure was published as early as 1970 (Miller OL Jr et. al. Science 1970) and shows an Electron Microscopy image of a bacterial genome that produces RNA and proteins in a coupled process.

© Miller, Science 1970.
Courtesy of the AAAS (American Association for the Advancement of Science).

The RNA

RNA has a very similar structure to DNA. However, while DNA contains deoxyribose as sugar, ribose is found in RNA instead.

Nucleotide: Single building block of RNA consisting of a phosphate group, a ribose and a nucleobase.

The RNA also consists of the nucleobases adenine (A), cytosine (C) and guanine (G), but instead of thymine (T) contains the nucleobase uracil (U). In contrast to DNA, RNA is often present as a single strand.

The four nucleobases in RNA:
A = adenine
U = Uracil
C = cytosine
G = guanine

RNA as single stranded molecule.

Interesting!

Only 2% of the human DNA encodes for proteins, but up to 95% are transcribed into RNA. According to various studies, the proportion of non-protein-coding DNA increases with the complexity of the organism. You can find more information here.

After an mRNA molecule is produced from a protein-coding gene, it has to undergo a maturation process before it can serve as a template for protein synthesis. An important step of this maturation is the process of splicing. You can read more about the process of splicing here.

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