Regulation Of Eukaryotic Gene Expression

Question 1

Site for regulation of gene expression

Answer 1

. Transcription control 
. Processing of primary transcript 
. RNA transport 
. Translational control 
. Posttransitional control

Question 2

Two levels of gene expression control

Answer 2

. Conversion of compacted chromatin to an extended structure (activation)
. Fine-tuning of transcription mediated by DNA-binding proteins/transcription factors (modulation)

Question 3

Types of transcription factors

Answer 3

. General transcription factors: abundant proteins that assemble on all genes transcribed by RNA polymerase II
. Gene regulatory proteins/specific transcription factors: proteins present in few copies in individual cells, perform functions by binding to DNA-specific nucleotide sequence, allows genes that they control to be activated or repressed

Question 4

Transcription factors structure

Answer 4

. Bind DNA as homo or heterodimers

. Contain unique structural motifs w/ precise AA sequence that determines particular DNA sequences that are recognized

Question 5

Transcription factors are important for ___

Answer 5

. Issue specific expression
. Cell growth and differentiation
. Lipid soluble soluble hormones bind their cognate receptors to regulate transcription in target cells

Question 6

The absolute rate that a gene is transcribed is regulated by ____

Answer 6

Number of polymerase that are synthesizing RNA from the gene sequence
. Transcription factors modulate this

Question 7

Domains in regulatory proteins that activate transcription

Answer 7

. Modular design
. One domain w/ structural motif that recognized specific DNA sequences
. Domain that contacts transcriptional machinery and accelerates rate of transcription initiation by accelerating assembly of general transcription factors at promoter site

Question 8

Transcriptional control of erythropoietin gene

Answer 8

. Hypoxia inducible factor (HIF) bind hypoxia response element (HRE) in gene in hypoxic conditions
. HIF-1alpha (only present in hypoxia) and beta (always present) make dimer at HRE site after alpha moves into nucleus
. Result is upregulation of EPO gene expression

Question 9

How is HIF-1alpha degraded in normal oxygen conditions?

Answer 9

. Normally hydroxylated via prolyl hydroxylase
. Causes binding of E3 ubiquitin ligase (VHL protein)
. Resulting polyubiquination caused by its degradation by the proteasome

Question 10

Alternative Splicing

Answer 10

. Ability of genes to form multiple proteins by joining different exon segments in primary transcript
. Happens by RNA binding proteins changing the accessibility of different splicing sites by masking a site or changing the local RNA structure to promote splicing of alternate sites
. Explains why genome Harper genes than there are proteins

Question 11

Alternative splicing in calcitonin gene

Answer 11

. In thyroid cells, cleavage of transcript to make calcitonin occurs at polyA site 1
. In brain, same transcript that makes calcitonin undergoes alternative splicing to produce calcitonin-gene related protein that cleaves at poly A site 2 (site 1 is masked by transcription factor proteins)

Question 12

T/F majority of nuclear RNA is degraded by nucleases before they move into cytoplasm for translation

Answer 12

T, helps prevent inappropriate gene expression

Question 13

Steady state of individual RNA species in a cell is determined by ____

Answer 13

Rate of transcription and rate of decay

Question 14

Stability of mRNA is influenced by signals inherent in ____

Answer 14

The 3’ untranslated region (UTR) and poly A tail

Question 15

How 3’ UTR influences stability of mRNA?

Answer 15

. 3’ UTR sequences form stem-loop structure for protein-binding and protection from degradation

Question 16

Transferrin receptor

Answer 16

. Receptor protein in cell membranes that permits cells to take up transferrin (protein that transports iron in blood)
. Rate of synthesis inc. when omtracellular Fe is low
. Regulated by binding of Fe-response element binding protein (IRP) to iron response element (IRE)

Question 17

How transferrin receptor mRNA is regulated

Answer 17

. The IREs are hairpin loops at 3’ end of mRNA
. When IRP doesn’t have bound iron, it has a high affinity for IRE hairpin loops
. IRP prevents degradation of mRNA when Fe is low, permitting more transferrin receptor synthesis

Question 18

What occurs to transferrin receptor mRNA when Fe levels are high?

Answer 18

. IRP binds to Fe and has low affinity for IRE loops
. W/o protein masking the IRE at 3’ end of mRNA it gets degraded
. Ends up in transferring receptors not being synthesized

Question 19

What occurs to ferritin mRNA when iron is low?

Answer 19

. Ferritin transcript has an IRE hairpin lop at the 5’ end of mRNA
. When low iron, IRP binds to IRE and ferritin synthesis is blocked because the translators proteins are sterically hindered and cannot attach to site to being synthesis

Question 20

What occurs to ferritin mRNA when iron is high?

Answer 20

. Iron blocks IRP from binding the IRE on the 5’ end of the mRNA
. Ferritin is synthesized because there is no more steric hindrance

Question 21

What regulates globin synthesis in reticulocytes?

Answer 21

. Lack of heme activates heme kinase to turn off globin synthesis