AP BIOLOGY

Detailed explanation-1: -Single-stranded RNA (ssRNA) is the simplest form of genetic molecule and constitutes the genome in some viruses and presumably in primitive life-forms. However, an innate and unsolved problem regarding the ssRNA genome is formation of inactive double-stranded RNA (dsRNA) during replication.

Detailed explanation-2: -RNA is always single-stranded and is often referred to as single-stranded ribonucleic acid. This can be seen in Figure 1 below. However, DNA can be either double-stranded or a single strand of DNA (ssDNA).

Detailed explanation-3: -A tRNA, like the one modeled below, is made from a single strand of RNA (just like an mRNA is). However, the strand takes on a complex 3D structure because base pairs form between nucleotides in different parts of the molecule. This makes double-stranded regions and loops, folding the tRNA into an L shape.

Detailed explanation-4: -So the correct answer is ‘TMV’.