lecture 23 - eukaryotic gene regulation

• How does chromatin structure affect gene expression in eukaryotes?

  It regulates the accessibility of genes for transcription

  
• How do control elements and transcription factors work together?

  They regulate gene expression by facilitating transcription initiation

  
• What is meant by "steady state" levels of expression in a cell?

  The balance between the rate of synthesis and degradation of mRNA and proteins

  
• What happens when allolactose binds to the lac repressor?

  The lac repressor does not bind to the operator, increasing transcription

  
• What occurs when tryptophan binds to the trp repressor?

  The trp repressor binds to the trp operator, inhibiting transcription

  
• What would be the consequence of a mutation preventing the repressor of an inducible operon from binding the operator?

  There would be continuous transcription of the operon’s genes

  
• How can you increase the production of human growth factor inserted into the E. coli lactose operon?

  By providing an inducer that activates the operon

  
• What are the differences between heterochromatin and euchromatin?

  • Heterochromatin: Closed chromatin, less accessible for transcription
  • Euchromatin: Open chromatin, more accessible for transcription

  
• How does the modification of transcripts affect gene expression?

  It influences the stability and translation of mRNA

  
• What is the role of the 5' cap in mRNA?

  It helps ribosomes attach to the 5' end of the mRNA

  
• What is the function of the poly-A tail in mRNA?

  It prevents the mRNA from being hydrolyzed

  
• What is alternative splicing?

  A process that expands the repertoire of a eukaryotic genome by producing different mRNA variants

  
• How does the turnover of mRNA and proteins influence gene expression?

  It determines the steady-state levels of mRNA and proteins in the cell

  
• What are the key components of gene expression regulation in eukaryotes?

  • Chromatin structure
  • Transcription factors
  • mRNA processing
  • Protein/mRNA degradation
• What is the significance of mPEGES-1 in gene expression?

  It encodes for microsomal prostaglandin E synthease-1
• What are positive and negative control elements in gene regulation?

  Positive control elements enhance gene expression, while negative control elements inhibit it
• Inducible operons are usually off, but can be turned on by inducers, which are bound to the operator and induce transcription.
• Repressible operons are usually on, but can be turned off by corepressors, 1 of which is the repressor and the other a corepressor bound to the 1st.
• DNA winds around core particles to form nucleosomes, which pack and form chromatin fiber
• Histone is DNA wrapped around a protein
• Histone Acetylation


  Create open and relaxed chromatin structure, allowing for transcription factor binding and RNA polymerase activation
• How is transcription initiation regulated?


  RNA polymerase requires assistance of transcription factors (TATA box) to initiate transcription.

  Transcription factors bind to DNA, then transcription initiation complex forms.
• Control Elements (distal)


  Segments of non-coding DNA that serve as binding sites for transcription factors & activators
• Bound activators facilitate a sequence of protein-protein interactions that result in enhanced transcription.
• Repressors are proteins that inhibit (transcription) the expression of genes by blocking access to promoter regions or preventing them from binding to the DNA
• Combinatorial Control of Gene Activation


  A mechanism in eukaryotic cells where multiple transcription factors combine to regulate gene expression, leading to diverse outcomes.
• Enhancers

  Regions of DNA that increase gene transcription by binding to transcription factors.
• Distal Control Element (DCE)


  A type of enhancer that regulates gene expression from a distance (10-100 kb away) from the gene.
• Capping and Polyadenylation


  The 5' end of pre-mRNA is capped with a 7-methylguanosine (m7G) cap, while the 3' end is modified with a poly(A) tail.
• Alternative Splicing of Alpha Tropomyosin Gene


  • Alternative Splicing: The process by which a single gene yields multiple, different mRNA transcripts through different combinations of exons.
  • Alpha Tropomyosin Gene: A gene that codes for alpha tropomyosin, a protein involved in muscle contraction.
  • Multiple Transcripts: The alpha tropomyosin gene produces multiple transcripts by using different donors and acceptors for splicing, resulting in different protein isoforms.
• Steady-state level of mRNA is maintained by the rate of transcription and the rate of degradation leading to a constant level of mRNA in the cell. If either the synthesis or degradation rate changes, it will temporarily disrupt the steady state until a new equilibrium is reached.
• The steady-state level of a protein in a cell is determined by the balance between its translation (its synthesis) and degradation via different cellular mechanisms (breakdown). A change in either synthesis or degradation will lead to a shift in the steady-state level until a new balance is established.
• Methylation

  Epigenetic modification that adds a methyl group to DNA or histone proteins; can silence or regulate gene expression, and lead to chromatin condensation by neutralizing positive charges on histone proteins.
• Acetylation

  Epigenetic modification that adds an acetyl group to histone proteins; increases gene expression by relaxing chromatin structure, and leads to chromatin decondensation by removing positively charged histone tails.