Video Transcript
When is a gene said to be expressed? (A) A gene is expressed when it becomes visible within the cell. (B) A gene is expressed when the sugar it codes for is made in the cell. (C) A gene is expressed when it is replicated within the cell. (D) A gene is expressed when the protein it codes for is made in the cell. Or (E) a gene is expressed when its DNA base sequence is irreversibly changed.
This question is asking us to choose the answer that best describes the process of gene expression. All living cells contain DNA, and a section of that DNA is called a gene. Gene expression is also called the central dogma of biology because it’s so important and it happens the same way in all living organisms. The central dogma states that DNA is transcribed into RNA and that RNA is translated into a sequence of amino acids, which are eventually folded into a functional protein. This process is the same among humans, plants, fungi, and even single-celled organisms like prokaryotic bacteria and eukaryotic paramecium.
The sequence of the DNA bases determines the sequence of the RNA bases, which determines the sequence of amino acids generated by a gene. The sequence of amino acid is folded into its functional shape, and this molecule is called a protein. Proteins consist of tens to hundreds of amino acids folded into a distinct shape. And the shape of a protein determines its function in the same way that the shape of a wheel determines its function.
We tend to think of DNA as controlling the cell. However, all the work in the cell is actually done by proteins. In living organisms, proteins do just about everything. Proteins control the characteristics of an organism as well as the functioning of cells and the maintenance of homeostasis. Knowing all of this, we can easily choose the correct answer to our question. A gene is said to be expressed when the protein it codes for is made in the cell.
