In later chapters, you will learn more about the regulation of gene expression. One way to regulate gene expression is to make changes to the histone proteins to alter how tightly the DNA is coiled and wrapped. The more tightly coiled and wrapped a particular region of DNA is, the less likely it is that the genes in that region will be expressed. Bearing this in mind, how tightly do you think regions of heterochromatin are compacted?

Question

A.  Very tightly
B.  Moderately
C.  Loosely
D.  Not at all

Clarify Question
  · What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

  Gather Content
  · What do you know about gene expression? How does it relate to the question?

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

  Reflect on Process
  · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

A.  Very tightly

Clarify Question
  · What is the key concept addressed by the question?
        o The question asks about the role of DNA bound to histones in gene expression.
· What type of thinking is required?
        o You are being asked to apply your knowledge of the effects of histone binding in heterochromatin on gene expression.
· What key words does the question contain and what do they mean?
        o Heterochromatin – tightly wound DNA bound to histones.  
        o Histones are positively charged proteins that bind to negatively charged DNA.

  Gather Content
  · What do you know about gene expression? How does it relate to the question?
        o For a gene to be expressed, enzymes like RNA polymerase need access to the DNA to synthesize RNA from the DNA template.

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?
        o If a region of DNA is loosely bound to histones and not at all compacted, the genes would be more likely to be expressed.

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Since heterochromatin domains are not expressed, the DNA must be very tightly compacted in those regions.

  Reflect on Process
  · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to apply your understanding of gene expression to predict if heterochromatin is tightly bound to histones. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall that heterochromatin genes are not expressed?  Could you make the connection that tightly wound heterochromatin genes could not be accessed and expressed?