RNA

RNA is a nucleic acid similar to DNA but usually single-stranded. It contains ribose sugar (instead of deoxyribose) and uses <u>uracil (U) in place of thymine</u>. RNA plays multiple roles in cells, including serving as the intermediary between DNA and proteins.

• Types of RNA include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). mRNA carries genetic code from DNA; tRNA and rRNA help assemble proteins.
• Unlike the double-stranded DNA, RNA is typically single-stranded. It can fold into complex shapes and even have enzymatic activity (as in ribozymes).
• RNA can be found in both the nucleus and cytoplasm. For example, mRNA is synthesized in the nucleus and then exported through nuclear pores to the cytoplasm for translation.
• Some viruses use RNA as their genetic material. (This is an exception to DNA as the genetic material - notable in RNA viruses like influenza or HIV.)

• If you see a nucleic acid described with uracil (U) bases or ribose sugar, the question is about RNA (not DNA). For instance, "single-stranded molecule with A, U, C, G bases" points to RNA.
• Transcription and translation questions often involve RNA. E.g., a question might ask what molecule carries the genetic code from nucleus to ribosome - answer: mRNA (a type of RNA).
• Be ready to distinguish RNA vs DNA functions. An exam might describe an experiment where genetic material is RNA (like certain viruses), testing if you know that not all genomes are DNA.