Gene Control

2026 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Describe the differences between structural genes and regulatory genes and the differences between repressible enzymes and inducible enzymes
  2. Explain genetic control of protein production in a prokaryote using the lac operon (knowledge of the role of cAMP is not expected)
  3. State that transcription factors are proteins that bind to DNA and are involved in the control of gene expression in eukaryotes by decreasing or increasing the rate of transcription
  4. Explain how gibberellin activates genes by causing the breakdown of DELLA protein repressors, which normally inhibit factors that promote transcription

What is Gene Control?

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Gene control means controlling when and how much a gene is expressed (turned on or off). Even though all cells in your body contain the same DNA, not all genes are active in every cell. For example, only certain cells in your pancreas make insulin, even though every cell has the insulin gene.

Gene control ensures that:

  • The right proteins are made
  • In the right amounts
  • At the right times
  • In the right cells

This control happens mainly at the level of transcription (making mRNA from DNA). If transcription doesn't happen, the protein won't be made.

Structural Genes vs Regulatory Genes

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Genes can be divided into two main types based on what they do:

Structural Genes

Structural genes code for proteins that have a functional role in the cell. These proteins actually do jobs in the cell.

Examples include:

  • Enzymes (like lactase, which breaks down lactose)
  • Hormones (like insulin)
  • Structural proteins (like collagen)
  • Transport proteins (like channel proteins in membranes)

Think of structural genes as the genes that make the "workers" of the cell.

Regulatory Genes

Regulatory genes code for proteins that control the expression of other genes. These proteins don't do the actual work in the cell, but they control whether other genes are switched on or off.

Examples include:

  • Transcription factors (proteins that bind to DNA and control transcription)
  • Repressor proteins (proteins that block transcription)

Think of regulatory genes as the genes that make the "managers" of the cell.

Key Difference

  • Structural genes → Make proteins that do jobs
  • Regulatory genes → Make proteins that control other genes

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