Chap 14C - O&C Eu

Describe STF + its 2 types

• Bind to specific non-coding DNA sequences known as control elements to regulate the rate of transcription

2 types of STF : 

1. One group binds to the proximal control element, located near the promoter

2. Another group of STF (activators or repressors) binds specifically to the distal control elements (enhancers or silencers)

Describe activators

• Are proteins that increase / upregulate the rate of transcription by binding to enhancers -> facilitate assembly and correct positioning of transcription initiation complex on promoter

Describe function of activators (DNA bending proteins)

• Trigger DNA looping mechanisms with the help of DNA bending proteins

• This brings the activator close to the promoter to interact with the transcription initiation complex

• The interaction will upregulate the activity of RNA polymerase to increase the rate of transcription of amylase gene to produce more protein

Describe repressors

• Proteins which interfere with transcription initiation or reduce the rate of transcription when bound to silencers

Describe functions of repressors

1. Repressor can also block the binding of an activator protein to the enhancer sequence

2. Repressor can bind to and mask the activation domain of an activator protein to prevent it from interacting with the transcription initiation complex

3. Repressor can also package whole regions of the eukaryotic chromatin into heterochromatin that is normally resistant to transcription

1. Repressor can also recruit histone deacetylases to the promoter for histone modifications to condense the chromatin at the promoter region, making it less accessible

Compare control at transcriptional level + type of mRNA produced for pro vs eu

Compare control at post-transcriptional level pro VS eu

Describe half-life of RNA

• The more stable (longer half-life) an mRNA is, the longer it remains in the cytoplasm and the more times it can serve as a template for the translation of more proteins

• By modulating the half-life of specific mRNA transcripts, cells can adjust the abundance of corresponding proteins -> enables cells to rapidly adapt to new stimuli and maintain homeostasis 

• Half life influenced by: 

1. Presence of 5’ cap

• Shields the mRNA against degradation by 5’ exonucleases

2. Presence 3’ poly-A tail 

• Acts as a buffer against degradation by 3’ exonucleases

  • Reduced poly-A tail decrease half-life of mRNA -> reduce time mRNA has to be translated -> reduce amount of polypeptides produced 

3. Binding of inhibitors which slow down degradation of mature mRNA by exonucleases in the cytoplasm

NOTE: Even though 5’ capping and 3’ polyadenylation occur during PTCM, , their effects in terms of regulation of gene expression are seen at the translational level

Describe translation initiation regulation

• Sequence-specific RNA binding proteins (translational repressors) bind to the 5’ UTR of mRNA and prevent ribosome binding and formation of translational initiation complex

• Sometimes, a RNA molecule complementary to the 5’ UTR regulates translation initiation by binding to the 5’ UTR to block the binding to ribosomes

Compare control at translational level pro VS eu