Transcription in Eukaryotes

lesson 5

In eukaryotes chromosomes must blank before transcription

unwind

What are the three different promoter sections in on genes for RNA pol 2?

1. core promoter

2. regulatory promoter

3. enchancer

What two most common consensus motifs are on the core promoter?

1. TATA box at -25

2. TF2D recognition element

Is the enhancer located upstream of the coding sequence?

no, can be upstream or downstream

The basal transcription apparatus is a?

general transcription factor

Where does the basal transcription factor bind?

to the core promoter

Where do transcriptional activator proteins bind?

to regulatory and enhancer sequences.

What are the job of transcriptional activator proteins?

high levels of transcription

What is an important general transcription factor for eukaryotic transcription?

TF2D (acts like sigma factor in bacteria)

What is the mediator in transcription eukaryotes?

a complex of proteins that mediate the interaction between activator RNA and general transcription factors

In initiation how does TF2D become connected to the DNA molecule?

the TATA binding protein binds TF2D to the tata box

What happens after TF2D binds to tata box?

Holoenzyme and RNA pol 2 can bind to the TF2D

What is DNA looping?

It allows the enhancer to interact with the core promoter.

What does the mediator protein do?

allows the regulatory promoter to interact with the core promoter.

How is RNA elongated?

5’ to 3’

How does RNA pol 1 terminate?

a transcription factor like rho that binds to dna sequence downstream of termination site.

How does RNA pol 3 terminate?

transcribes a terminator sequence similar to the string of uracil nucleotides in an rna molecule. Similar to rho independent in bacteria

What is the first step in termination for rna pol 3?

synthesis of RNA past the coding sequence.

What is the second step in termination for RNA pol 3?

cuts pre-mRNA to leave a cleavage site.

What binds at the cleavage site in RNA pol 2?

rat 1 enzyme and it continues in 5’ to 3’ until it reaches rna polymerase.

What is the addition of a 5’ cap in in pre-mRNA processing?

guanine nucleotides and methyl groups

what is the purpose of the 5’ cap?

translation initiation.

What is the addition of a poly a tail?

at the 3’ site PAP adds adenine

What is the recognition sequence for poly a tail?

AAUAAA

What is an exon?

protein coding sequences of the transcripts

What is an intron?

non coding sequences between exons on the transcript

Are introns common?

yes but not guaranteed.

Pre-mrna contains what conserved sequences?

5’ 3’ site and a point brand A.

What recognizes the sequences on the premrna?

spliceosome which consists of 5 snRNAS and almost 300 proteins.

How are introns removed?

spliceosome binds at splice site recognition and forms a lariat structure to remove it.

What 3 modifications are made to pre-mrna?

1. 5’ cap

2. poly a tail

3. splicing introns removed

What is alternative processing?

a very common process that results in multiple mRNA and protein products

What is RNA editing?

Pre-mrna can be altered after trasncription using guide mRNA