Central Dogma Molecular Influences on Genetic Regulation

Transcription Overview

3 Parts to Transcription

Prokaryotic vs. Eukaryotic Promoter Region vs Start of Transcription Promotor recognition site (for RNA polymerase) located 20 to 30 bp UPSTREAM from the start of transcription

Animation: TATA Box Binding Protein

Regulation of Gene Expression in Eukaryotes 1.Control at Initiation of Transcription 2. Alternative Splicing on Exons 3. Controlling access to transport channels (nuclear pores – exit out of nucleus) 4. Degrading of mRNA – in the cytoplasm 5. Controlling rate of Translation - in the ribosome 6. Post-Translational Modification

Receptor Regulated Gene Expression (common in eukaryotes) Animation 1.Small fat-soluable molecules pass into the cell and bind to proteins needed to start transcription 2.Molecule binds to protein and activates transcription 1.Inhibitor Protein is Removed 2.Transcriptional Protein bind to DNA 3.Transcription of Gene is activated

Prokaryotic Regulatory Proteins Animation Animation Negative Control – Repressor/Inducer (AraC) A REPRESSOR protein can bind to DNA ( at silencer site) and block transcription ( sometimes needs the assistance of a co-repressor) (sometimes) Compound that interacts with repressor (inducer) – binds to it – block repression [e.g. Arabinose] Positive Control – Activator An ENHANCER protein binds to the DNA (at enhancer site) enables RNAP to bind to DNA (better) and enables & improves transcription (sometimes) Activator, starts transcription, NEEDS an Inducer If inducer is not present, activator can’t bind = no transcription

LAC Operon Animation Animation The ability of bacteria to use lactose is controlled by an Operon (cluster of functionally related genes can be under coordinated control by a single on/off “switch”) 2 proteins control this operon – Catabolite Activator Protein (CAP) [activator] and Lac Repressor Protein [repressor] CAP needs cyclic AMP [inducer] to bind to the Operon When glucose is present (high) cAMP is low… What effect will this have on the Operon (on or off)?

Elongation RNA polymerase (RNAP) starts building the single-stranded mRNA in the direction of 5’ to 3’ – does not require a primer (unlike DNA replication) – promoter does not get transcribed – Prokaryotes have 1 RNAP – Eukaryotes have 3 (RNAP I, RNAP II,RNAP III); RNAP II transcribes mRNA and RNAP III transcribes tRNA RNA polymerase uses only one of the strands of DNA as a template for mRNA synthesis. Chosen DNA strand is called the template strand Strand that is not used is known as the coding strand RNA sequence - complementary to the template strand and identical to the coding strand, except that it contains uracil instead of thymine

Termination Prokaryotes: Rho-dependent Termination: a termination factor called rho-factor to stop RNA synthesis at specific sites; causes RNAP to dissociate from the DNA, terminating transcription ANIMATIONANIMATION OR Rho-Independent Termination: encounters a sequence with many Gs & Cs causes a knot to the RNA strand, RNA detaches from the DNA template Eukaryotes: RNAP II Complex reaches termination signal – string of Ts followed by G-C rich hairpin-loop, the RNAP i detaches from the DNA allowing it to rewind