Final answer:
Introns are non-protein-coding sequences removed from pre-mRNA during processing in the nucleus of eukaryotic cells. Not all eukaryotic genes contain introns, and those within mitochondrial and chloroplast genes can also contain introns. Introns can contain regulatory information, and their correct removal is essential for protein synthesis.
Step-by-step explanation:
Among the statements provided about introns and exons, none accurately describes the relationship between these genetic elements in eukaryotic genes. Eukaryotic genes are composed of exons, which correspond to the protein-coding sequences (the term ex-on signifies that they are expressed), and non-coding sequences called introns (int-ron denotes their intervening role). Introns are indeed non-coding regions within genes and are removed from pre-mRNA during processing in the nucleus, not in the cytoplasm. It is not accurate to say that all eukaryotic genes contain an intron, as there are exceptions. Moreover, introns can sometimes contain sequence-specific information which is significant for the regulation of gene expression and alternative splicing, so they're not simply 'junk' DNA without any information content. Also, mitochondrial and chloroplast genes can contain introns in some species; they are not universally devoid of introns. Therefore, the most accurate description would gravitate around the understanding that while introns do not encode for proteins, they may have regulatory functions and their precise removal is critical for the synthesis of functional proteins through a process known as splicing, conducted by spliceosomes.