Final answer:
Cardiac cells and brain cells share the same DNA but express different subsets of genes to create distinct proteins needed for their specialized functions. This process, known as gene expression, allows for cell differentiation despite the common genetic material.
Step-by-step explanation:
The correct answer to your question is that same DNA being used to make different proteins is true when comparing cardiac (heart) cells to brain cells. While all somatic cells in the human body have essentially the same DNA, the expression of genes varies between different types of cells. This means that each type of cell activates or "expresses" a different subset of genes to create the range of proteins needed for its unique functions. For example, specific proteins responsible for the functions of the heart, such as those in pacemaker cells or heart muscle, are expressed primarily in the cardiac cells, while other proteins required for brain functions are expressed in the brain cells.
Therefore, despite having the same internal structures, like the nucleus containing DNA and ribosomes for protein synthesis, these cells differentiate in their structure and function due to gene expression. This expression of specific genes is precisely regulated to ensure cells become specialized according to their role within the body, such as maintaining heart rhythm or conducting neural impulses in the case of the brain.