The diagram represents a single strand of DNA containing a gene, in purple. Remember this gene is "read" in the 5' to 3' direction to produce an mRNA. To make a protein (polypeptide), mRNA is translated, or read, three nucleotides at a time. Each triplet codon specifies an amino acid to be added to the growing polypeptide chain. In addition to the amino acid designations, specific "start" and "stop" codons begin and end the protein sequence.
The majority of eukaryotic mRNAs contain a tract of A residues at the end. These polyA-tails are not encoded in the DNA. Rather, they are added to the pre-mRNA "post-transcriptionally" (after transcription). The end of pre-mRNA is cut by a specific enzyme
Students reveal their preconceptions about depression, then use G2C Online to learn about symptoms of the disorder, genes, and neurotransmitters associated with it, and challenges involved in diagnosis and treatment.