Nutrition Science and Everyday Application - beta v 0.1

310 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
basic musical notes. Similarly, the 20 amino acids can be linked together in an extraordinary
number of sequences. For example, if an amino acid sequence for a protein is 104 amino
acids long, the possible combinations of amino acid sequences is equal to 20 104 , which is 2
followed by 135 zeros!
BUILDING PROTEINS WITH AMINO ACIDS
The decoding of genetic information to synthesize a protein is the central foundation of
modern biology. The building of a protein consists of a complex series of chemical reactions
that can be summarized into three basic steps: transcription, translation, and protein
folding.
Figure 6.3. Overview of protein synthesis. Protein folding happens after translation.
1. Transcription – Deoxyribonucleic acid, or DNA, is the long, double-stranded
molecules containing your genome—instructions for making all of the proteins in
your body. In the nucleus of the cell, the DNA must be transcribed or copied into
the single-stranded messenger ribonucleic acid (mRNA), which carries the genetic
instructions into the cell’s cytosol for protein synthesis.
2. Translation – At the ribosomes in the cell’s cytosol, amino acids are linked
together in the specific order dictated by the mRNA. Each amino acid is connected
to the next amino acid by a special chemical bond called a peptide bond (Figure
6.4). The peptide bond forms between the carboxylic acid group of one amino acid