Lecture 10: Regulation of eukaryotic Gene Expression

Question 1

Chromatin modification –>

Answer 1

transcription –> RNA processing –>

mRNA degradation OR translation –> protein processing and degradation

Question 2

DNA is wrapped around __ that make up ___

Answer 2

histones

chromatin

Question 3

Nucleosome:

Answer 3

8 histones + 146 base pairs of DNA

Question 4

tightly packed chromatin :

Answer 4

• heterochromatin
• associated with methylated DNA
• INACCESSIBLE for transcription

Question 5

lightly packed chromatin :

Answer 5

• euchromatin
• associated with un-methylated DNA
• ACCESIBLE for transcription

Question 6

tightly packed chromatin to lightly packed chromatin –>

Answer 6

• histone acetyl transferases

- histone methyl transferases

Question 7

lightly packed chromatin to tightly packed chromatin

Answer 7

• histone deacetylase

- histone demethylase

Question 8

the ‘inactive’ state of RNA polymerase ll

Answer 8

• RNA polymerase is NOT bound to gene promoter

- Gene + promoter are typically cytosine-methylated and associated with tightly packed chromatin

Question 9

the ‘paused’ or ‘stalled’ state of RNA polymerase ll

Answer 9

• Some transcription factors bind to regulatory elements in promoter
• RNA polymerase ll binds to promoter and is phosphorylated at Serine 5, but remains inactive

Question 10

the ‘elongation’ or ‘active’ state of RNA polymerase ll

Answer 10

• More transcription factors bind to regulatory elements in promoter
• RNA polymerase ll becomes phosphorylated at Serines 2 & 5, which triggers the transcription progress

Question 11

RNA processing: splicing and alteration of mRNA ends

Answer 11

• transcription forming pre-mRNA

- pre-mRNA converted to Mature mRNA as Adenine added to ends and removal of introns (non coding DNA)

Question 12

RNA processing: ‘alternative’ splicing

Answer 12

• transcription to produce pre-mRNA
• pre-mRNA converted to either mRNA variant A (added A and full removal of introns) or mRNA variant B (added A and partial removal of introns) = two different tissues

Question 13

small RNAs two types:

Answer 13

• microRNA (miRNA)

- small interfering RNA (siRNA)

Question 14

small RNAs are

Answer 14

double stranded and between 20 and 30 nucleotides long

Question 15

Small RNAs repress (prevent)

Answer 15

gene expression via 3 mechanisms

Question 16

three mechanisms of small RNAs repressing gene expression:

Answer 16

1) Repressor of gene translation: miRNA
2) promote mRNA degradation: miRNA
( both 1&2 = ‘post-transcriptional gene silencing’)
3) Repession of gene transcription via chromatin remodelling and DNA methylation: siena & piRNAs
(‘transcriptional gene silencing’

Question 17

post-transcirptional gene silencing by miRNAs

Answer 17

• pre-miRNA = hairpin shaped
• miRNA double stranded by H-bonds
• Dicer comes along breaks end hairpin joint
• forms miRNA-proteni complex
• either mRNA degraded OR translation is blocked

Question 18

the proteasome degrades

Answer 18

ubiquitin-tagged proteins

Question 19

Ubiquitin is a

Answer 19

small (8.5kDa) protein regulating turn-over of other proteins

Question 20

Addition of multiple Ubiquitins targets the protein for

Answer 20

DEGRADATION

1) Multiple ubiquitin molecules are attached to a protein by enzymes in the cytosol
2) the ubiquitin-tagged protein is recognised by a proteasome, which unfolds the protein and sequesters it within a central cavity
3) Enzymatic components of the proteasome cut the protein into small peptides, which can be further degraded by the other enzymes in the cytosol