Introduction - Logic Synthesis for Genetic Diseases - page 3

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Promoter Gene

DNA

Transcription

RNA

Translation

Amino acid chain

Folding

Protein

Fig. 1.3 Transcription and translation of gene to RNA and protein

(amino acid) takes place with the help of RNA in a process called transcription and
translation (Fig. 1.3 ).
When a protein is needed by the cell, the nucleotide sequence of the gene is first
copied to another type of nucleic acid, RNA, which is similar to DNA but with
the 4 nucleotide bases: A, G, C, U. The RNA strand then serves as a template for
protein synthesis. A specific molecule called polymerase latches onto the start site
of the gene and slides along the DNA, synthesizing the complementary RNA at the
same time. This process of copying gene DNA into RNA strands is referred to as
transcription . When a gene is being transcribed, it is said to be expressed , or turned
ON. If no transcription is taking place, then the gene is said to be not expressed, or
turned OFF.
After the RNA strand is produced, the RNA nucleotide sequence has to be decoded
to produce the appropriate protein. This translation process takes place with the use
of other functional molecules called ribosomes among others, which read the RNA
strand and bind the complementary amino acids to form a chain. The resulting amino
acid chain folds to create the final protein.

1.2.2 Gene Expression Regulation

While the genome of an organism encodes all functional molecules that are needed to
make and maintain its cells, not every gene needs to be expressed all the time. A cell