Biology Reference
In-Depth Information
somal deletions encompassing this gene have been reported, ranging from
250 kb to several megabases (Huber et al. 1994). This region of the X chro-
mosome appears to be gene-poor because hearing loss (resulting from dele-
tion of the
POU3F4
gene) is most often the only phenotype.
3. From DNA to Protein: Transcription and Translation
The flow of information begins with the genetic material, the DNA. All cells
contain the same genetic material in the form of DNA, but the levels at
which this material is expressed, in the form of protein, varies between each
tissue. The process of “expression” is a complex one, involving many steps,
all of which may be affected by genetic mutations (Fig. 2.3). The first step,
DNA transcription, changes the DNA information into RNA. There are
three major types of RNA molecules produced by transcription: messenger
RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA).
mRNAs are utilized in the process of translation and are the template for
protein synthesis. rRNAs serve as structural components of the transla-
tional machinery, whereas tRNAs serve as the carriers that bring in new
amino acids for the growing peptide chain.
DNA is transcribed into mRNA in the nucleus. Sequences in the DNA,
termed promoters, are recognized by transcription factors that recruit
the RNA synthesis machinery to the gene and initiate RNA synthesis at
that site. After RNA synthesis is initiated, the growing RNA is elongated
until a termination signal is reached and the RNA synthesis machinery is
FIGURE 2.3. A schematic view of the flow of information within a cell, beginning
with DNA as the genetic material and ending with protein as the “expression” of
the genetic material. Mutations can occur at each of these steps. Modified with
permission from Pearson Education Limited (Carter and Murphey 1999).
