Which one of the following statements about unmutated nucleic acids is correct?
A. rRNA has anticodons which bind to tRNA.
B. Prokaryotic DNA is a single strand which forms a loop.
C. tRNA is made up of one phosphate-sugar backbone and may have adenosine and thymine bases.
D. mRNA is made up of a single nucleotide with a codon of uracil, cytosine and guanine bases.
E. Bases in DNA may form hydrogen bonds with uracil bases.
The correct answer is E.
First, what is a nucleic acid ?
The 2 main types of nucleic acids are the DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Their purpose is to :
Now, let’s review each item individually :
Transfer RNA or tRNA is important during protein synthesis : it serves as the adaptor between the messenger RNA and the chain of amino-acids that is being synthesized. In other words, it carries the amino-acids into the ribosome to enable protein synthesis. It contains an anticodon, which is made of 3 nucleotides, and serves to ensure proper protein synthesis. The anticodon is complementary to the messenger RNA or mRNA, thus making item A incorrect.
The difference between prokaryotes and eukaryotes is the fact that their DNA is not surrounded by a nuclear membrane. In other words, the have no nuclei : instead, they have a structure called the nucleoid. Single strand DNA is found in DNA viruses but NOT prokaryotes (like bacterias and archeas). While they do contain circular DNA, it is a double-stranded.
tRNA is made up of a single strand of RNA. Because it is made of RNA, it does NOT contain thymine but uracil instead : thymine does NOT occur in RNA.
mRNA is made up of a single-stranded molecule of RNA. It is relatively short (~2kb) and made up of four nucleotides : adenine, uracil, guanine and cytosine, thus making item D false.
Uracil is the demethylated form of thymine and bonds to adenine. Adenine being common to both RNA and DNA structures, it is possible for a DNA strand to form hydrogen bonds with uracil bases.