Single-stranded ribonucleic acid (RNA) can fold up and twist to form 3-D structures like this transfer RNA (tRNA). During protein synthesis, tRNA binds and delivers an amino acid to the ribosome, which adds the amino acid to the growing protein chain.
Credit or Source: Protein Data Bank (www.rcsb.org) PDB ID 4TNA visualized using iMol
US DOE. Genomics Placemat: Genomics for Energy and Environmental Science, US Department of Energy Office of Science. (p. 2) (website)