1. DNA mRNA Transcription Cell Polypeptide (protein) Translation Ribosome Transcription

2. Protein Synthesis Flow of Information: DNA RNA Proteins Transcription Translation 1. Transcription is the process by which a molecule of DNA is copied into a complementary strand of RNA. 2. This is called messenger RNA (mRNA) because it acts as a messenger between DNA and the ribosomes where protein synthesis is carried out.

3. Protein Synthesis Transcription Transcription process 1. RNA polymerase (an enzyme) attaches to DNA at a special sequence that serves as a “start signal”. 2. The DNA strands are separated and one strand serves as a template. 3. The RNA bases attach to the complementary DNA template, thus synthesizing mRNA.

4. Protein Synthesis: Transcription Transcription process continued 1. The RNA polymerase recognizes a termination site on the DNA molecule and releases the new mRNA molecule. 2. mRNA leaves the nucleus and travels to the ribosome in the cytoplasm.

5. Protein Synthesis: Transcription

6. Both processes use DNA as the template. Phosphodiester bonds are formed in both cases. Both synthesis directions are from 5´ to 3´. Similarity between replication and transcription

7. replicationtranscription templatedouble strandssingle strand substratedNTPNTP primer yesno EnzymeDNA polymeraseRNA polymerase productdsDNAssRNA base pairA-T, G-CA-U, T-A, G-C Differences between replication and transcription

8. DNA Cytoplasm Nucleus Eukaryotic Transcription Export G AAAAAA RNA Transcription Nuclear pores G AAAAAA RNA Processing mRNA

9. Eukaryotic transcription Three RNA polymerases One for each major type of RNA – RNApoly I -makes pre-rRNA – RNApoly II -makes pre-mRNA – RNApolyIII - makes pre-tRNA Each polymerase has a different promoter structure

10. RNApoly II promoter Initiator sequence surrounding the start point TATA box at about –25 bp TATA+Initiator = core promoter A transcription factor binds to the TATA box before RNAPoly II