Question: On a single strand of DNA, can both sense and antisense sequences exist?
About the article "DNA", section "Sense and antisense".

Candidate passages:
A DNA sequence is called "sense" if its sequence is the same as that of a messenger RNA copy that is translated into protein.
The sequence on the opposite strand is called the "antisense" sequence.
Both sense and antisense sequences can exist on different parts of the same strand of DNA (i.e.
both strands can contain both sense and antisense sequences).
In both prokaryotes and eukaryotes, antisense RNA sequences are produced, but the functions of these RNAs are not entirely clear.
One proposal is that antisense RNAs are involved in regulating gene expression through RNA-RNA base pairing.
A few DNA sequences in prokaryotes and eukaryotes, and more in plasmids and viruses, blur the distinction between sense and antisense strands by having overlapping genes.
In these cases, some DNA sequences do double duty, encoding one protein when read along one strand, and a second protein when read in the opposite direction along the other strand.
In bacteria, this overlap may be involved in the regulation of gene transcription, while in viruses, overlapping genes increase the amount of information that can be encoded within the small viral genome.
The two complementary strands of double-stranded DNA (dsDNA) are usually differentiated as the "sense" strand and the "antisense" strand.
The DNA sense strand looks like the messenger RNA (mRNA) and can be used to read the expected protein code by human eyes (e.g.
ATG codon = Methionine amino acid).
However, the DNA sense strand itself is not used to make protein by the cell.
It is the DNA antisense strand which serves as the source for the protein code, because, with bases complementary to the DNA sense strand, it is used as a template for the mRNA.
Since transcription results in an RNA product complementary to the DNA template strand, the mRNA is complementary to the DNA antisense strand.
The mRNA is what is used for translation (protein synthesis).
Hence, a base triplet 3'-TAC-5' in the DNA antisense strand can be used as a template which will result in an 5'-AUG-3' base triplet in mRNA (AUG is the codon for Methionine, the start codon).
The DNA sense strand will have the triplet ATG which looks just like AUG but "will not be used to make Methionine" because it "will not be used to make mRNA".
The DNA sense strand is called a "sense" strand not because it will be used to make protein (it won't be), but because it has a sequence that looks like the protein codon sequence.
Students may find this confusing if they misunderstand the meaning of "sense" and if they misunderstand complementation.
To make things more confusing, before the convention was set, very early textbooks disagreed on the DNA strands called "sense" and "antisense.
"In biology and research, short antisense molecules can interact with complementary strands of nucleic acids, modifying expression of genes.
See the section on "antisense oligonucleotides" below. 
In genetics, a sense strand, or coding strand, is the segment of double-stranded DNA running from 5' to 3' that is complementary to the antisense strand of DNA, which runs from 3' to 5'.
The sense strand is the strand of DNA that has the same sequence as the mRNA, which takes the antisense strand as its template during transcription, and eventually undergoes (typically, not always) translation into a protein.
The immediate product of this transcription is a resultant initial RNA transcript, which contains sequencing of nucleotides that are identical to the sense strand.
The exception to this is that uracil is used for nucleotide sequencing of RNA molecules rather than thymine.
Most eukaryotic RNA transcripts undergo additional editing prior to being translated for protein synthesis.
This process typically involves removal of introns from the initial RNA transcript, the addition of a methylated guanine nucleotide cap at the 5' end, and the addition of a poly-A tail at the 3' end.
This deletion process is known as splicing.
The end product is known as a mature mRNA.
Prokaryotic mRNA does not undergo the same process.
Strictly speaking, only the mRNA makes "sense" with the genetic code, as the translated protein peptide sequence can be directly inferred from this strand.
The "antisense" strand of DNA is complementary to the "sense" strand and is the actual template for mRNA synthesis.
Knowing the difference between the sense and antisense strands is important in certain molecular biology applications.
For example, in microarray expression technologies, it is important to know which strand is "viewed" on the array.
An array can correspond to either strand; however, a single array will be made entirely of "sense" or "antisense" strands.
Identifying the different strands is also important in understanding small interfering RNAs, or siRNA. 
In biological systems, nucleic acids contain information which is used by a living cell to construct specific proteins.
The sequence of nucleobases on a nucleic acid strand is translated by cell machinery into a sequence of amino acids making up a protein strand.
Each group of three bases, called a codon, corresponds to a single amino acid, and there is a specific genetic code by which each possible combination of three bases corresponds to a specific amino acid.
The central dogma of molecular biology outlines the mechanism by which proteins are constructed using information contained in nucleic acids.
DNA is transcribed into mRNA molecules, which travels to the ribosome where the mRNA is used as a template for the construction of the protein strand.
Since nucleic acids can bind to molecules with complementary sequences, there is a distinction between "sense" sequences which code for proteins, and the complementary "antisense" sequence which is by itself nonfunctional, but can bind to the sense strand. 
Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid.
The chemical convention of naming carbon atoms in the nucleotide sugar-ring numerically gives rise to a 5′-end and a 3′-end (usually pronounced "five prime end" and "three prime end").
The relative positions of structures along a strand of nucleic acid, including genes and various protein binding sites, are usually noted as being either "upstream" (towards the 5′-end) or "downstream" (towards the 3′-end).
(See also upstream and downstream.
)This naming convention is important because nucleic acids can only be synthesized in vivo in the 5′-to-3′ direction, as the polymerase that assembles new strands only attaches new nucleotides to the 3′-hydroxyl (-OH) group, via a phosphodiester bond.
Directionality is related to, but independent from sense.
In coding DNA, codons read 5′–ATG–⋯–3′ on the sense strand, and 3′–TAC–⋯–5′ on the complementary antisense strand.
Thus only the "antisense" strand will be transcribed to sense (5′–AUG–⋯–3′) mRNA.
By convention, single strands of DNA and RNA sequences are written in 5′-to-3′ direction.