The MT-TL1 gene provides instructions for making a molecule called a transfer RNA (tRNA), which is a chemical cousin of DNA. Transfer RNAs help assemble protein building blocks (amino acids) into functioning proteins. The MT-TL1 gene provides instructions for making a specific form of tRNA that is designated as tRNA<html:sup>Leu(UUR)</html:sup>. During protein assembly, this molecule attaches to the amino acid leucine (Leu) and inserts it into the appropriate locations in the growing protein.~The tRNA<html:sup>Leu(UUR)</html:sup> molecule is present in cellular structures called mitochondria. These structures convert energy from food into a form that cells can use. Within mitochondria, tRNA<html:sup>Leu(UUR)</html:sup> is involved in the assembly of proteins that carry out a series of chemical steps called oxidative phosphorylation. This process uses oxygen, simple sugars, and fatty acids to create adenosine triphosphate (ATP), the cell's main energy source.~In certain cells in the pancreas, called beta cells, mitochondria also play a role in controlling the amount of sugar (glucose) in the bloodstream. In response to high glucose levels, mitochondria help trigger the release of a hormone called insulin. Insulin regulates blood glucose levels by controlling how much glucose is passed from the blood into cells to be converted into energy.