Lecture 26 - Eukaryotic Transcription Flashcards Preview

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Flashcards in Lecture 26 - Eukaryotic Transcription Deck (9)
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1
Q

What do the different eukaryotic polymerases do?

A

RNA pol 1: rRNA
RNA pol II: mRNA
RNA pol III: tRNA and 5S rRNA segment

2
Q

How does RNA pol 1 work?

A

Has 2 transcription factors: TF1B and TF1S to help with Binding the promoter and Stabilizing the binding
Makes rRNA in a 45s segment that is then spliced into three pieces to ensure 1:1 ratio of ribosomal units

3
Q

How does RNA pol II work?

A

Synthesizes mRNA in the pre-mRNA form, which is then processed. mRNA is monocistronic (no operons, genes for proteins with functions in same pathway are located all over genome)
Has 2 types of transcription factors: 1) promoter-proximal, TF2D binds to the TATA box via the TATA binding protein, allows the RNA pol 2 and other transcription factors to bind
2) Enhancer elements: located upstream, work as activators

4
Q

How does TBP work?

A

Binds to the minor groove via concave surface, bends and spreads minor groove, TBP intercalats between base pairs and creates kink in DNA to allow for RNA pol 2 docking

5
Q

How are eukaryotic genes regulated?

A

Only positively regulated through enhancer elements. Negative regulation occurs naturally through the chromatin binding in a solenoid which prevents transcription from occurring. Positive regulation has activators binding to enhancer elements to increase transcription at nearby promoters. Activators linked to promoter TFs through co-activators which form a mediator complex intermediary, which allows activators to communicate with pol and TFs. Activators can help recruit RNA pol2

6
Q

What are the 3 types of mRNA processing?

A

5’ cap, poly-A tail, splicing the introns out

7
Q

How does 5’ capping work?

A

7-methylguonosine (methylated guanine) added in 5’-5’ triphosphate linkage to the 5’ end during transcription, protects it from nucleases, helps ribosomes initiate translation

8
Q

How does polyadenylation work?

A

Synthesize RNA beyond the cleavage signal sequence (contains AAUAAA), protein complex has endonuclease to cleave ~20 bases downstream of cleavage signal, then polyadenylate polymerase adds A residues to protect mRNA from nucleases

9
Q

What are 3 common DNA binding motifs?

A

Zinc finger domains: alpha helix and loop stabilized by zinc ion, binds to the major groove
homeodomain: 3 alpha helices with hydrophobic interactions, helix 3 interacts with bases in the major groove, helix 1 interacts with bases in the minor groove
Leucine zipper: 2 alpha helices that dimerize via hydrophobic interactions between leucine side chains every 7 residues, interact with DNA in the major groove