mRNA

Messenger RNA is a single-stranded RNA copy of a gene that serves as a template for protein synthesis. mRNA is transcribed from DNA in the nucleus and carries the genetic message to the cytoplasm, where ribosomes translate that message into a protein.

• An mRNA molecule is essentially a "messenger" between DNA and protein: it has a sequence of codons (three-base sequences) that specify amino acids.
• In eukaryotes, a mature mRNA has a 5' cap and a 3' poly-A tail, which protect it and help it interact with ribosomes. These features distinguish mRNA from other RNA types.
• mRNA is transient. Cells constantly produce, use, and degrade mRNAs. This allows regulation of protein production - short-lived mRNAs mean protein isn't made for long.

• If a question asks which molecule carries genetic code from the nucleus to ribosomes, the answer is mRNA. A classic clue is "RNA that codes for protein".
• Questions about codons usually point to mRNA. For example, "which RNA contains codons for amino acids-" -> mRNA (because tRNA has anticodons, not codons).
• Be careful not to confuse mRNA with other RNAs on exams. If the context is carrying information or the result of transcription, it's mRNA (not tRNA or rRNA).