KEY CONCEPT Transcription is the process of converting the DNA’s code for one gene into an RNA strand.

DNA has the code but RNA carries DNA’s instructions to the ribosomes DNA must remain “safe” in the nucleus while RNA can leave to carry the gene’s code to the ribosome

RNA: Ribonucleic Acid RNA differs from DNA in three major ways. (1) RNA is a single-stranded molecule. (2) RNA has a ribose sugar as its 5-carbon sugar (3) RNA has uracil instead of thymine.

Transcription copies DNA’s code to make a strand of RNA Why? Make an expendable copy to send out of the nucleus DNA can stay safe in nucleus When? At the start of Protein Synthesis Where? In the nucleus

How? (1) An enzyme recognizes the start of a gene and “unzips” the weak hydrogen bonds in DNA. start site nucleotides transcription complex

RNA polymerase moves along the DNA (2) Free-floating RNA nucleotides attach to the left strand of the DNA, forming hydrogen bonds. (nucleotide=sugar+phosphate+base) DNA RNA polymerase moves along the DNA

Covalent bonds are created. RNA pulls away from the DNA and the DNA strands “zip” back up. RNA