Gene transcription is controlled by regulatory elements on DNA that either activate or repress transcription. In prokaryotes, this typically involves an operon, such as the lac operon in E. coli. In eukaryotes, regulation of transcription is more complex. It generally includes regulatory elements such as the TATA box and homeobox genes that switch other regulatory genes on or off.
- CA.9–12.IE.1.d; CA.9–12.LS.4.d
- NSES.9–12.A.1.6; NSES.9–12.C.1.4, 6
- AAAS.9–12.5.B.6; AAAS.9–12.5.C.6; AAAS.9–12.6.B.1
- Identify general mechanisms that regulate gene expression.
- Describe how gene regulation occurs in prokaryotes.
- Give an overview of gene regulation in eukaryotes.
gene expression: use of a gene to make a protein
homeobox gene: gene that codes for regulatory proteins that control gene expression during development
operator: a region of an operon where regulatory proteins bind
operon: region of prokaryotic DNA that consists of a promoter, an operator, and one or more genes that encode proteins needed for a specific function
regulatory element: region of DNA where a regulatory protein binds
regulatory protein: protein that regulates gene expression
TATA box: regulatory element that is part of the promoter of most eukaryotic genes
Introducing the Lesson
Introduce gene regulation with an analogy. Tell students that the genes we inherit are like the hard drive of a computer, but each type of cell has its own separate “software.” The “software” turns on or off a particular set of genes through the mechanisms of gene regulation. Tell students they will learn how genes are regulated in this lesson.
Suggest that students watch the online animation below. It demonstrates the lac operon mechanism for gene regulation.
Pair less proficient readers with more proficient readers, and ask pairs to work together to make a main ideas/details chart for the lesson. Suggest that they try to write a main idea for each heading and subheading in the lesson and include at least one detail per main idea. LPR
This lesson focuses on transcriptional regulation of gene expression. Have interested students research translational regulation. Ask them to summarize at least one translational regulation mechanism, such as microRNA-mediated regulation, and present their summary to the class. Encourage them to make a diagram to help explain the mechanism.
Challenge groups of students to formulate a hypothesis for how the lac operon evolved. They should consider why it might be advantageous for an organism to be able to control the production of proteins that it needs only in certain situations, rather than produce the proteins all the time. Give groups a chance to share and discuss their hypotheses.
Elaborate on the connection between gene regulation and cancer that is presented in the lesson. Explain that tumor-suppressor genes normally act like “brakes” to inhibit cell growth and division, whereas proto-oncogenes normally act like “gas pedals” to accelerate cell growth and division. When mutations occur in these genes, it’s similar to the cells to losing their brakes and hitting the gas pedal. The cells grow and divide uncontrollably. Students can learn more by watching the video at the URL below.
Reinforce and Review
Copy and distribute the lesson worksheets in the CK-12 Biology Workbook. Ask students to complete the worksheets alone or in pairs as a review of lesson content.
Have students answer the Review Questions listed at the end of the lesson in the FlexBook®.
Points to Consider
Scientists know more about human chromosomes and genes than they know about the genetic material of most other species. In fact, scientists have identified all of the approximately 20,000-25,000 genes in human DNA.
- What do you know about human chromosomes and genes? For example, do you know how many chromosomes humans normally have?
- Do you know how human characteristics are inherited? Can you identify characteristics that are controlled by a single gene?