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Molecular and Cell Biology > L10 Regulation of gene expression > Flashcards

L10 Regulation of gene expression Flashcards

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1
Q

Why do microorganisms adapt their profile of expressed genes?

A

To utilize available nutrients

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2
Q

How is cell diversity in multicellular organisms achieved?

A

The diversity of cell type in multicellular organisms reflects different protein profiles that are dependent upon distinct transcript patterns.

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3
Q

What are the two main categories of gene expression?

A
  1. House keeping genes - constituvently expresses
  2. Regulated genes - can be induced or repressed.
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4
Q

What drives changes in a gene expression?

A

Cell differentiation and development programmes.

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5
Q

What is a key principle of regulated gene expression?

A

The key principle is the sequence specific binding of proteins to regulatory elements within DNA or RNA.

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6
Q

What are the two types of mutation that can affect gene expression?

A

Mutations affecting the regulated expression of a gene can be in cis (within the same gene) or in trans (in a different gene).

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7
Q

What is the difference between cis and trans mutations?

A
  1. cis mutations: identify DNA/RNA sequences that affect gene regulation.
  2. trans mutations: identify (protein or RNA) factors that regulate the expression of a target gene.
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8
Q

At what level is most genes regulated?

A

Transcription level

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9
Q

What is transcriptional regulation? (2)

A
  1. Transcriptional regulation is the primary level of control for most genes.
  2. Transcriptional regulation limits wasteful production of unrequired biomolecules.
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10
Q

How do transcription factors regulate gene expression?

A

Transcription factors can act to up- or downregulate expression.

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11
Q

What are trans-acting activators and repressors?

A
  1. Factors that cause activation are known as trans-acting activators. Upregulated genes are under positive control.
  2. Factors that cause downregulation are known as trans-acting repressors. Downregulated genes are under negative control.
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12
Q

What is the role of activators at weak promoters?

A

Activators promote expression at weak promoters.

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13
Q

How do activators in E. coli interact with RNA polymerase?

A

Activators in E. coli interact with the α-subunit of RNA polymerase and promote DNA binding.

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14
Q

How is the activity of transcriptional activators and repressors regulated?

A

The activity of transcriptional activators and repressors can be regulated through interaction with other molecules. These molecules can stimulate or inhibit activity of the transcription factor.

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15
Q

What are inducers and corepressors?

A
  1. Inducers bind to transcription factors and stimulate activators or inhibit repressors.
  2. Corepressors bind to transcription factors and stimulate repressors or inhibit activators.
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16
Q

How can genes under positive or negative control be regulated?

A

Genes under positive or negative control can be induced and/or repressed.

17
Q

What are the three genes that lac operon encodes?

A

lacZ, lacY and lacA.

18
Q

What controls the expression of lac operon?

A

Expression of the lac operon is controlled by the transcription repressor gene, lacI.

19
Q

Where does the lac repressor bind to block RNAP activity?

A

The lac repressor binds to lacO operator sequences and blocks RNAP activity.

20
Q

How is the Lac repressor regulated?

A

DNA binding activity of the lac repressor is inhibited by inducer molecules such as lactose.

21
Q

What is CAP?

A

The lac operon is also regulated by a transcriptional activator called catabolite activator protein (CAP).

22
Q

How does the lac operon respond to glucose and lactose levels?

A
  1. CAP binds to the lac promoter when associated with the inducer cyclic AMP and stimulates transcription.
  2. cAMP production is inhibited in the presence of glucose (a preferred carbon source).
  3. The lac operon is expressed only in the absence of glucose and presence of lactose.
23
Q

How is lac expression regulated?

A

Lac expression is inducible and under both positive and negative control.

24
Q

At what level is gene expression regulated in eukaryotes? (1)

A

They are regulated at the level of RNA processing.

25
Q

What is alternative splicing?

A

Pre-mRNA splicing can occur in different patterns, leading to the production of two distinct proteins from the same pre-mRNA. Alternatively, there might be a nonproductive pathway, in which the mRNA is degraded.

26
Q

How can gene expression be regulated?

A

Gene expression can be regulated at the level of translation.

27
Q

What are the two main ways translation can be regulated?

A
  1. Global level: Translation can be downregulated in eukaryotic cells as part of the integrated stress response (ISR).
  2. Transcript-specific level: Expression of the mRNA encoding the iron-binding protein ferritin is responsive to cellular Fe2+ levels.
28
Q

Where is translation typically regulated?

A

Translation is normally regulated at the initiation step.

29
Q

What is post-translational modification?

A

Phosphorylation of serine, threonine or tyrosine residues is the most common form of post-translational modification.

30
Q

How does phosphorylation affect a protein?

A

Phosphorylation often affects a protein’s ability to interact with other molecules.

31
Q

What enzymes regulate phosphorylation?

A

Phosphorylation is readily reversible. Phosphorylation is driven by protein kinases and reversed by phosphatases.

32
Q

What happens to eIF2 during translation initiation?

A

During translation initiation, eIF2 hydrolyses GTP to GDP.

33
Q

How is the eIF2/GTP complex regenerated?

A

Regeneration of the eIF2/GTP complex requires the initiation factor eIF2B.

34
Q

What is the effect of ISR on eIF2?

A

The ISR leads to the phosphorylation and inactivation of the α subunit of eIF2.

35
Q

What happens to phosphorylated eIF2α?

A

Phosphorylated eIF2α binds very tightly to eIF2B and is trapped in a complex that cannot be recycled.

Molecular and Cell Biology (23 decks)

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