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The Central Dogma of Molecular Biology

Updated on May 12, 2010

Information Flow in Biological Systems

The "Central Dogma" refers to the flow of genetic information in biological systems. In general, genetic information flows from DNA to RNA to protein. DNA (deoxyribonucleic acid) encodes the genetic information for most species. In order to use this information to produce proteins, the DNA must first be converted into a messenger RNA (ribonucleic acid) through a process called transcription. The information carried by the mRNA is then used to construct a specific protein (or polypeptide) through a process called translation. Each polypeptide then performs a specific function in the cell.

DNA Replication

DNA-->DNA

Every cell needs a copy of the genome in order to function; therefore a mechanism must exist by which an exact (or almost exact) copy of the genome is made prior to cell division. That mechanism is DNA replication.

The main player in the process of DNA replication is the enzyme DNA polymerase. DNA polymerase is responsible for recognizing one strand of the parent DNA double helix and making a DNA copy that exactly compliments that template. This process is called semi-conservative replication because each new DNA helix consists of one parent strand and one new (or daughter) strand.

In order to do this, DNA polymerase must be able to read the nucleotides on the template strand, find complimentary nucleotides in the cellular pools, and link those nucleotides into a new DNA strand which will ultimately form a new double helix with the parental template strand.

The animations linked below will help you to better understand this process!

Transcription

DNA --> RNA

Before protein synthesis can occur, specific regions of the genome called genes must be converted into RNA. This process is called transcription (copying from one nucleic acid language into another).

The main player in this process is RNA polymerase. RNA polymerase is responsible for recognizing a gene on one strand of the DNA template and making an RNA copy that exactly compliments that template. A given gene will be transcribed many times ((hundreds or even thousands) into messenger RNA (mRNA) molecules that will be used in the process of translation.

The animations linked below will help you to better understand this process!

Translation

RNA-->Protein

Proteins are the molecules that carry out the specialized functions of the cell. Proteins are encoded at the genomic level by specific segments of DNA called genes. Genes are transcribed into mRNAs which are then translated (moving from nucleic acid language into amino acid language) into polypeptides (or proteins).

The main player in the process of translation is the ribosome . Ribosomes are large structures in the cell, consisting of many proteins and ribosomal RNA (rRNA) molecules. Ribosomes are responsible for recognizing mRNAs, reading the nucleic acid code, and producing a chain of amino acids that corresponds to that code. In order to carry out this function, ribosomes rely on transfer RNA (tRNA) to read complimentary base pairs in groups of three nucleotides called codons on the mRNA. Each tRNA carries a specific amino acid that corresponds to the codon that it recognizes and, as sequential tRNAs deliver their amino acids to the ribosome, the ribosome links the amino acids into a polypeptide via a series of peptide bonds.

The animations linked below will help you to better understand this process!

Retroviruses - Variations on a Theme

Retroviruses, like HIV, carry an RNA genome which is converted into DNA prior to its insertion into the human genome. In order to carry out this conversion, the RNA must be reverse transcribed into DNA. Retroviruses produce a special enzyme called reverse transcriptase which, conveniently, performs the process of reverse transcription (RNA-->DNA). Once the viral DNA is inserted into the human genome, the standard rules of the central dogma apply.

Prions - Just Plain Weird

Prions (Proteinaceous Infectious Particles) are infectious agents that appear to have a unique method of information transfer. Prions are proteins - in other words, they do not carry a genome. As such, the standard rules of the central dogma do not apply to prions. Prion diseases, such as Mad Cow, are thought to result from the interaction of misfolded prion proteins with normal prion proteins. These interactions result in the misfolding of the normal prion proteins (information transfer) and, ultimately, the typical spongiform encephalopathy associated with prion diseases.

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