Lecture 14 - Overview of eukaryotic gene expression

Question 1

How many genes do E.coli and humans ghve?

Answer 1

E.coli
~4000
Humans
~27000

Extra DNA in eukaryotes contains a lot of regulatory info

Question 2

What structures in the eukaryotic genome are used to specify which cells transcribe a gene?

Answer 2

-complx combinations of regulatory DNA elements (enhaners)
-change during embryo genesis e.g.
Even skipped
-expression in developing fly embryo is in 7 transmembrane stripes
-segmented embryo has eve expressed in alternate segments

Question 3

What are the multiple control points for euakryotic gene expression?

Answer 3

• DNA packaging
• transcription
• RNA processing
• mRNA stability/targeted RNA degradation
• RNA export and localisation
• translation
• post-translational modification
• protein stability/degradation

Question 4

What are the proportions of RNA that are rRNA, tRNA and mRNA?

Answer 4

rRNA = ~80%
tRNA = ~15%
mRNA = ~5%

Most RNA is non coding

Question 5

How many multisubunit RNA polymerases do eukaryotes have and what are there specific functions?

Answer 5

3
RNA pol I (rRNA)
RNA pol II (mRNA) 
-simplest structure (12 subunits)
RNA pol III (tRNA)
-most complex (17 subunits)

Question 6

What is the distribution of genes in humans that are coding/noncoding?

Answer 6

~23000 protein encoding gene

~4000 noncoding genes

Question 7

How does the organisation of eukaryotic genomiv material present a challenge for transcription?

Answer 7

• contained within nuclei in which DNA id densely packed in chromatin
• low accessibility (access to genes is sometime blocked by chromatin)
• access to genes is regulatd by enzymes that modify and remodel chromatin

Question 8

What is required for RNA pol recruitment to genes?

Answer 8

• multiple transcription factirs

- different cell types have different combinations of transcription factors

Question 9

What is the process of production of mature mRNA?

Answer 9

1. Primary RNA transcript is transcribed from the template strand and as transcription continues the 5’ end is capped (imp for the efficiency of translation)
2. endonuclease cleaves at the Poly(a) site
3. Poly(A) polymerase (PAP) along with ATP polyadenylates the transcript to stabilise it (must happen quickly)
4. RNA spicing to remove introns and produce mRNA

Question 10

Outline an extreme example of how differential splicing offers considerable oppourtunity for regulation and diversification

Answer 10

Alterantive spilicing of drosophila Dscam RNA
-potential to produce huge protein diversity from a single gene
-12 variants of exon 4
-48 vairants of exon 6
33 variants of exon 9
2 variants of exon 17=> over 38000 possible Dscam isoforms-

Question 11

What are miRNAs?

Answer 11

regulate mRNA stability and or translation

• short pieces of RNA 21 nucleotides long
• can bind to mRNA by sequence compliemtarity

Question 12

What is nonsense-mediated decay?

Answer 12

-ensures that mRNAs with premature termination codons are eliminated as templates for translation

Question 13

Difference between eukaryotic and prokaryotic ribosomes?

Answer 13

bigger in eukaryotes

• greater complexity in TF controlling the assembly and regulation of transcription
• 13 eukaryotic translation initation factors, only 3 in bacteria

Question 14

What is the function of multiple post translational modifications and give an extreme example

Answer 14

To regulation the function of eukaryotic proteins
e.g. p53
Undergoes
-ubiquitination
-phosphorylation 
-acetylation 
-glycosolyation 
-methylation
-neddylation 
-sumolation