From DNA to Protein
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From DNA to Protein

How does DNA lead to a protein. Read about it here. Transcription and translation are explained and fitted in the larger process of protein synthesis.

The Basics

DNA is structured as a double helix, with its fundamental building blocks being nucleotide bases (adenine, cytosine, guanine and thymine). Together these form genes, which code for a protein. In order to arrive at the finished protein, there are two important processes that need to be initiated:

  • Transcription, and
  • Translation.

Transcription

When an original DNA helix is unwound, the nucleotide bases are used as templates for the production of new complementary DNA strands (G binds with C, and A with T). these new complementary strands are subsequently used as templates for an RNA strand. This RNA is referred to as messenger RNA (m-RNA) since it transports the message of the DNA out of the cellular nucleus to be processed.

As the transcription furthers along its template, this is read and transcribed. A large precursor is made, which is called heterogeneous nuclear RNA (hn-RNA) and possesses both introns and exons. Through a process called splicing, the introns are removed and the exons are joined together. The end of the transcription is indicated by a stop codon on the template (usually TAA, TAG or TGA).

Processing the m-RNA

When the m-RNA is finally produced, it gets a cap and a tail. These stabilize the molecule during transport. When the introns are removed, and the exons joined, the m-RNA is ‘ripe’ to leave the nucleus and enter the cytoplasm with the important genetic information.

Translation

As the m-RNA leaves the nucleus, it moves towards one or several ribosomes in the cytoplasm. These ribosomes translates the code in groups of three bases (the so-called codons). Each codon represents an amino acid. Since codons are ‘written’ in RNA, the base thymine is replaced by uracil. There are four bases and each codon is made up out of three bases, so in total 64 different codons are possible (4 to the third). As man only uses 20 amino acids, there are multiple codons for one amino acid.

The m-RNA strand slides through the ribosome, which reads and translates the code. As this happens, a molecule transfer RNA (t-RNA) brings the right amino acid to the ribosome. All these amino acids are bound together by the ribosome using peptide bonds. After the complete translation is done, a protein is created.

Summary (see figure)

The genes (nucleotide base sequences coding for a protein)on DNA (1) are transcribed from a complementary DNA strand by m-RNA (2), which brings this info to the ribosomes. Here, the code is translated per three bases (codons) which code for one amino acid (3). These are bound together and will eventually form a full-fledged protein (4), ready to fulfill one of its numerous potential functions.

(Image source: http://publications.nigms.nih.gov/thenewgenetics/chapter1.html)

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