Regulation of gene expression

Question 1

What does constitutively expression mean?

Answer 1

The gene is continuously expressed, no matter the conditions

Question 2

What is the name given to proteins that bind to specific regulatory sequences within DNA and RNA?

Answer 2

Trans-acting factors

Question 3

What are cis sequence elements?

Answer 3

Sequences in DNA or RNA that’s being regulated

Question 4

What do cis and trans mutations mean?

Answer 4

-cis occurs in the same gene
-trans occurs in different genes

Question 5

What do cis and trans mutations identify?

Answer 5

-cis - identify DNA/RNA sequences that affect regulation
-trans - identify factors that regulate expression of target gene

Question 6

What level are most genes regulated at and why?

Answer 6

-transcription level
-limits wasteful production of unrequired biomolecules

Question 7

What can transcription factors do to translation?

Answer 7

Activate or repress transcription

Question 8

What do trans-acting activators do?

Answer 8

-activate transcription
-upregulated genes are under +ive control
-promote expression at weak promoters
-interact with alpha-subunit of RNA polymerase + promote DNA binding

Question 9

What do trans-acting repressors do?

Answer 9

-cause downregulation
-under -ive control

Question 10

What do inducers do?

Answer 10

Stimulate activators or inhibit repressors

Question 11

What does corepressors do?

Answer 11

Stimulate repressors or inhibit activators

Question 12

What does Lac Operon encode and what is it’s expression controlled by?

Answer 12

-3 genes linked with lactose metabolism - lacZ, lacY, lacA
-controlled by transcription repressor gene lacI

Question 13

What does the Lac repressor do?

Answer 13

Binds to lacO operator sequences, blocking RNAP activity

Question 14

What is CAP?

Answer 14

-catabolite activator protein
-a transcriptional activator

Question 15

How is lac Operon activated by CAP?

Answer 15

-CAP binds to lac promoter when associated with inducer cyclic AMP + stimulated transcription
-cAMP production inhibited in presence of glucose
-lac Operon expressed only in absence of glucose + presence of lactose

Question 16

What does it mean to say that Lac expression is inducible?

Answer 16

It’s under both +ive and -ive control

Question 17

How can gene expression be regulated in eukaryotes during RNA processing?

Answer 17

-pre-mRNA splicing can occur in different patterns
-different pathways can result in 2 functional proteins or 1 functional + 1 non-functional protein

Question 18

How can gene expression be regulated at translation?

Answer 18

-normally at initiation step
-translation is downregulated in eukaryotes as part of the integrated stress response (ISR)
-can also be regulated by transcript-specific mechanisms
-expression of mRNA coding the iron-binding protein ferritin is responsive to Fe2+ levels

Question 19

How can protein function be regulated by post-translational modifications?

Answer 19

-changes to protein structure after translation
-most common form = phosphorylation of serine, threonine or tyrosine residues

Question 20

How does phosphorylation affect protein function?

Answer 20

-affects the proteins ability to interact with other molecules
-is readily reversible
-driven by protein kinases + reversed by phosphatases

Question 21

How is translation inhibition by phosphorylation of eIF2 alpha?

Answer 21

-during translation, eIF2 hydrolyses GTP to GDP
-regeneration of eIF2/GTP complex requires eIF2B (initiation factor)
-ISR leads to phosphorylation + inactivation of alpha subunit of eIF2
-phosphorylated eIF2 alpha binds tightly to eIF2B + is trapped in a complex that can’t be recycled