DNA

mRNA

Transcription

Cell

Polypeptide(protein)

TranslationRibosome

Transcription

Protein Synthesis

Flow of Information:DNA RNA Proteins Transcription Translation1. 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.

Protein Synthesis Transcription

Transcription process1. 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.

Protein Synthesis: Transcription

Transcription process continued1. 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.

Protein Synthesis: Transcription

• 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

replication transcription

template double strands single strand

substrate dNTP NTP

primer yes no

Enzyme DNA polymerase RNA polymerase

product dsDNA ssRNA

base pair A-T, G-C A-U, T-A, G-C

Differences between replication and transcription

DNA

Cytoplasm

Nucleus

Eukaryotic Transcription

ExportG AAAAAA

RNA

Transcription

Nuclear pores

G AAAAAA

RNAProcessing

mRNA

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

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