Transcription and RNA’s role Ribonucleic Acid Section 12-3

RNA- Ribonucleic Acid A. RNA is a single stranded nucleic acid that contains the sugar RIBOSE, and contains the same phosphate as DNA.

I. What does RNA do? A. It is responsible for the movement of genetic information from the DNA in the nucleus to the site of protein synthesis (Ribosomes)in the cytosol.

II. Structure of RNA A. Made of three parts: 1. Sugar group: ribose 2. Phosphate group: same as DNA 3. Nitrogenous base: A,G,C and a new one, Uracil. a. Uracil takes the place of thymine in RNA and binds with adenine.

III. Three Types of RNA A. Messenger RNA (mRNA) 1. RNA in the form of a single uncoiled chain; carries genetic information from DNA to cytosol B. Transfer RNA (tRNA) 1. One chain about 80 nucleotides long; binds to mRNA and amino acids C. Ribosomal RNA (rRNA) 1. Bundles of RNA, makes up ribosomes

rRNA tRNA mRNA

IV. Transcription A. The process by which genetic information from DNA is copied in the nucleus to mRNA which carries it out to the cytosol.(ribosome)

Steps of Transcription 1. RNA polymerase, the primary transcription enzyme, attaches to DNA at specific areas called promotors (marks the beginning of a specific gene that will be transcribed.) 2. RNA polymerase unwinds that portion of DNA and uses only one chain as a template for transcription.

3. RNA polymerase begins adding complementary RNA nucleotides to the newly forming mRNA single chain. DNA RNA A >>>>>>>>>>>>> U G >>>>>>>>>>>>> C T >>>>>>>>>>>>> A C >>>>>>>>>>>>> G

4. RNA polymerase continues along the DNA chain until it reaches a termination signal (UGA, UAA, or UAG) 5. Termination Signal: A sequence of DNA nucleotides that tells the RNA polymerase to release the DNA chain. 1. A new single mRNA strand is made and released, transported out of the nucleus.

Differences between DNA and mRNA DNA mRNA Double strand Single strand Thymine Uracil Deoxyribose Ribose Cannot leave nucleus Can leave nucleus