Epigenetics

How to Use This In-Class Guide

  • Follow along with the slides and take notes.

Learning Objectives

  • 9.1: Diagram how signals are relayed from outside to inside the cell.

  • 9.2: Predict whether a signal will bind a cell surface receptor or an intracellular receptor based on its chemical properties.

  • 9.3: Sketch the different levels of DNA packaging from double helix to chromosomes.

  • 9.4: Describe how signals from outside the cell can result in changes in gene regulation.

Pre-Class Review

  1. Why do you have different types of cells in your body?

    • a. Because different cells have different genes.

    • b. Because different cells make different proteins.

    • c. Correct Answer: Because different cells have different genes and make different proteins.

  2. What happens when you are stressed?

    • Cortisol signals changes in the cells of your hippocampus, which helps you calm down.

  3. Receptor location depends on signal.

  4. Based on the structure of cortisol:

    • Do you think it binds to a membrane receptor or an intracellular receptor?

      • a. Membrane receptor

      • b. Intracellular receptor (likely answer, based on cortisol structure).

  5. How we classify a signal depends on how it travels to its destination.

  6. What kind of signaling is cortisol signaling?

    • a. Autocrine

    • b. Contact-dependent

    • c. Paracrine

    • d. Endocrine (answer, as cortisol is a hormone released into the bloodstream).

  7. Cortisol binds to a receptor called the glucocorticoid receptor (GR):

    • This receptor enters the __ of the cell and turns _ the expression of genes that help calm you down.

    • a. The (more/less) GR proteins you have, the better you can cope with stress and the less anxious you are.

  8. How is DNA packaged?

    • a. Histone: in complex, bound to DNA.

    • b. Nucleosome: DNA in complex with .

    • c. Chromatin: One double-stranded DNA _ and packaged with histones.

  9. Gene expression depends on how accessible the DNA is for transcription:

    • a. Acetylation of a histone:

      • Neutralizes the positive charge on the lysine residue of histones.

      • Result: releases DNA from histones.

    • b. Methylation:

      • -CH3 group added to cytosine of DNA.

      • Result: Recognized by proteins that help condense chromatin.

  10. What chemical property do you think the residues of histone proteins have?

    • a. Polar

    • b. Non-polar

    • c. Positive charge

    • d. Negative charge

  11. Chromatin is modified to either promote or prevent gene expression:

    • Graph how DNA methylation and histone acetylation each affect gene expression. [Note: Graph not included in text]

  12. Observation: Adult rats that were licked a lot by their mother in the first week of life are much less anxious than rats who were not licked.

    • a. Hypothesis: The amount of licking affects expression levels of the GR protein.

  13. If licking promotes expression of the GR gene, what would likely be true of the chromatin around/in the GR gene? (Select all that apply)

    • a. Histones would have a high level of acetylation.

    • b. Histones would have a low level of acetylation.

    • c. The DNA would have high levels of methylation.

    • d. The DNA would have low levels of methylation.

    • Correct Answers: (Selection needs to be determined based on understanding of gene expression linked to GR protein expression due to licking behavior).

Additional Notes

  • It is crucial for students to connect the theoretical knowledge of hormone signaling with practical observations in developmental biology (as seen in the rat licking experiment).