The Central Dogma of Molecular Biology
Transcription of DNA to RNA to protein: This dogma forms the backbone of molecular biology and is represented by four major stages.

A. The DNA replicates its information in a process that involves many enzymes: replication.
The major types of proteins, which must work together during the replication of DNA, are illustrated,
showing their positions. When DNA replicates, many different proteins work together to accomplish the
following steps:
1. The two parent strands are unwound with the help of DNA helicases.
2. Single stranded DNA binding proteins attach to the unwound strands, preventing them from winding
back together.
3. The strands are held in position, binding easily to DNA polymerase, which catalyzes the elongation of
the leading and lagging strands. (DNA polymerase also checks the accuracy of its own work!).
4. While the DNA polymerase on the leading strand can operate in a continuous fashion, RNA primer is
needed repeatedly on the lagging strand to facilitate synthesis of Okazaki fragments. DNA primase,
which is one of several polypeptides bound together in a group called primosomes, helps to build the
5. Finally, each new Okazaki fragment is attached to the completed portion of the lagging strand in a
reaction catalyzed by DNA ligase.

B. The DNA codes for the production of messenger RNA (mRNA) during transcription.
Process by which non-coding sequences of base pairs (introns) are subtracted from the coding
sequences (exons) of a gene in order to transcribe DNA into messenger RNA (mRNA.)
In chromosomes, DNA acts as a template for the synthesis of RNA in a process called transcription. In
most mammalian cells, only 1% of the DNA sequence is copied into a functional RNA (mRNA). Only one
part of the DNA is transcribed to produce nuclear RNA, and only a minor portion of the nuclear RNA
survives the RNA processing steps.

One of the most important stages in RNA processing isRNA splicing. In many genes, the DNA sequence coding for proteins, or “exons”, may be interrupted by stretches of non-coding DNA, called “introns”. In the cell nucleus, the DNA that includes all the exons and introns of the gene is first transcribed into a complementary RNA copy called “nuclear RNA,” or nRNA. In a second step, introns are removed from nRNA by a process called RNA splicing. The edited sequence is called “messenger RNA,” or mRNA.

The mRNA leaves the nucleus and travels to the cytoplasm, where it encounters cellular bodies called ribosomes. The mRNA, which carries the gene’s instructions, dictates the production of proteins by the ribosomes.

C. In eucaryotic cells, the mRNA is processed (essentially by splicing) and migrates from the nucleus to the cytoplasm.
D. Messenger RNA carries coded information to ribosomes. The ribosomes “read” this information and use it for protein synthesis. This process is called translation.
Process whereby DNA encodes for the production of amino acids and proteins.

This process can be divided into two parts:

1. Transcription
Before the synthesis of a protein begins, the corresponding RNA molecule is produced by RNA transcription. One strand of the DNA double helix is used as a template by the RNA polymerase to synthesize a messenger RNA (mRNA). This mRNA migrates from the nucleus to the cytoplasm. During this step, mRNA goes through different types of maturation including one called splicing when the non-coding sequences are eliminated. The coding mRNA sequence can be described as a unit of three nucleotides called a codon.

2. Translation
The ribosome binds to the mRNA at the start codon (AUG) that is recognized only by the initiator tRNA. The ribosome proceeds to the elongation phase of protein synthesis. During this stage, complexes, composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one, translated into polypeptidic sequences dictated by DNA and represented by mRNA. At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

One specific amino acid can correspond to more than one codon. The genetic code is said to be degenerate.

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