Video Transcript
Which of the following statements about DNA in prokaryotic cells is correct? (A) The nitrogenous bases that are contained in the DNA are A, T, G, and U. (B) The majority of the DNA does not code for proteins and has no obvious function. (C) The DNA is found loosely floating within the cell and is formed of less than 100 nucleotides. (D) The DNA is tightly wound around specialized proteins called histones and coiled into chromatin. Or (E) the DNA is coiled compactly, so if it was stretched out, it would be much longer than the cell itself.
Let’s start by remembering some of the basics of DNA. DNA uses four nitrogenous bases: adenine, thymine, guanine, and cytosine. RNA uses the base uracil instead of thymine, but DNA doesn’t use uracil as a base. So answer choice (A) is incorrect. Now let’s go over some of the features of prokaryotic DNA. Most of the DNA in prokaryotes is coding DNA, meaning that prokaryotic DNA sequences mostly code for proteins. In eukaryotes, much of the DNA is noncoding and doesn’t code for proteins. So answer choice (B) is incorrect because this is referring to eukaryotic DNA.
Prokaryotic genomes can range in size from hundreds of thousands of nucleotides to millions of nucleotides. So answer choice (C) is incorrect. Both prokaryotic and eukaryotic DNA is compacted. However, they do this in different ways. Eukaryotic DNA is wound around specialized histone proteins to form chromatin, while prokaryotic DNA is circular and is compacted by a process called supercoiling, which doesn’t involve histone proteins. So answer choice (D) is incorrect because this is describing eukaryotic DNA.
In fact, the DNA in prokaryotes is so compacted that if we took all the DNA out of the bacterium E. Coli and stretched it out, it would be about 1.4 millimeters, which is about 1000 times the size of the cell itself. Therefore, the statement that correctly describes DNA in prokaryotes is answer choice (E). The DNA is coiled compactly, so if it was stretched out, it would be much longer than the cell itself.
