Gene Expression (Regulation)

• When the trp operon is transcribed, what exactly is produced by RNA polymerase?

  a single long mRNA that includes the coding regions of all 5 genes in the operon
• If the levels of tryptophan are low in the environment, would you expect the trp operon to be "on" or "off"?


  on
• There are many steps in expressing a eukaryotic gene, including transcription, RNA processing, translation, and more, but the only opportunity to regulate gene expression occurs during transcription

  false
• Prokaryotic cells and eukaryotic cells regulate gene expression differently. What are some general rules?

  Eukaryotes regulate gene expression at all stages of the process whereas prokaryotes primarily regulate at the level of transcription
• Prokaryotes often organize groups of genes that will be needed together into blocks called

  operons
• In the trp operon, what "partner molecule" must bind to the repressor in order to get it to stop transcription of the operon?

  tryptophan - the co-repressor
• In the presence of lactose, transcription can occur because the inducer (allolactose) binds to 


  the repressor, causing it to unbind from the operator
• If lactose levels are low in an E. coli cell, where would you expect to find the repressor of the lac operon?

  bound to the operator region preventing transcription
• Under "default" conditions - meaning that lactose is not present, the lac operon is turned "off"


  true
• The cells of a multicellular organism all start out with the same DNA yet the individual cells function differently. Why is this?

  Each cell expresses only the subset of genes it needs for its functions at any given time
• As a general rule in prokaryotic gene expression, where does each kind of regulatory molecule bind?

  activators bind to the promoter region, while repressors bind to operator regions
• When CAP binds to the promoter region of the lac operon, transcription of the operon is repressed

  false
• What is the term for various strategies which produce long-term and inheritable changes in gene expression without making changes in the actual DNA sequence?

  epigenetics
• Removing histones from a section of DNA would have what predicted effect on transcription levels?


  it would allow transcription
• Adding acetyl groups to histone proteins neutralizes some of their positive charge. How does this affect DNA's association with histones?


  it loosens the winding of the DNA allowing the histone to move out of the way or be removed entirely
• One way to regulate levels of gene expression in eukaryotes is to control access to the DNA itself by altering the level of packaging (winding and folding) around the gene


  true
• Adding lots of methyl groups to C bases in the promoter of a gene tends to do what to its expression?

  decreases transcription levels - "silences" the gene
• Can epigenetic changes to DNA such as methylation patters be preserved and inherited by the next generation of cells (after DNA replication and cell division)?

  yes
• Enhancer regions may be located far away from the promoters of genes they regulate. Enhancer regions bind specific transcription factors, but may also require DNA bending proteins to bring the enhancer and promoter regions close together
• What binds to the TATA box?


  the general transcription factor TFIID
• Alternative splicing can be thought of as a form of gene expression regulation because after a pre-mRNA is made

  different combinations of exons may be chosen to create the mature mRNA producing different version of the final protein
• Prokaryotic cells use repressors to control transcription, while eukaryotic systems only use enhancers

  false
• All cells produce the same transcription factors and regulatory proteins, so all cells transcribe the same sets of genes


  false
• Many eukaryotic promoters are diverse and complex, and may contain binding sites for many proteins, including general transcription factors, RNA polymerase, and specific regulatory transcription factors

  true
• Cells have several mechanisms for control the stability (lifespan) of an mRNA molecule in the cytoplasm. Which mechanisms below relate to mRNA stability?

  addition of the 3' -polyA tail, addition of the 5' cap, and binding of RBPs to the 5' and 3' UTR regions
• Where are the binding sites for general (basal) transcription factors located?

  in the core promoter
• The translation rate and stability (lifespan) of an mRNA is increased when microRNAs bind to it

  false
• Transcription factors in eukaryotes fall into 2 broad classes. What is the name of the class that binds to the promoter and assists RNA polymerase in the transcription of all genes?


  general (or basal) transcription factors