• Compton College

• BIOLOGY 102 by
  Kristy J. Wilson
  School of Mathematics and Sciences
  Marian University, Indianapolis, IN

Answer Key for “Diabetes and Insulin Signaling” - Case Study Collection - National Center for Case Study Teaching in Science
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ANSWER KEY
for
“Diabetes and Insulin Signaling”
by
Kristy J. Wilson
School of Mathematics and Sciences
Marian University, Indianapolis, IN
Note: The answers to these questions are, in some cases, given in more detail than the student would
likely provide. This additional information is provided for the instructor, so that they can enrich the
discussion.
Part I – Research Orientation
1. What are the essential parts of a signaling pathway?
The essential parts of a signaling pathway are the initial signal, the receptor, and the signaltransduction protein or proteins. The signal-transduction protein(s) then lead to either shortterm or long-term effects.
2. How could activating a transcription factor cause long-term cellular changes?
A transcription factor (TF) is a DNA binding protein that functions to modulate the recruitment of
RNA polymerase. A TF can act in a positive way to stimulate transcription or in a negative way
to repress transcription. Activating a TF generally results in its translocation to the nucleus.
Activating a TF can cause long-term cellular changes by changing the protein composition of the
cell. Possible long-term cellular effects include stimulation of the cell cycle, responses to stress,
or production of enzymes involved in metabolism.
3. What roles can phosphorylation play in protein function?
Phosphorylation can happen on target proteins at seriene, theronine, or tyrosine residues and
can affect protein function. Depending on the protein and the site of phosphorylation (because
one protein can have many sites) phosphorylation can increase or decrease functionality. For
example, phosphorylation could cause the activation of an enzyme. Also different proteinprotein interactions are regulated by phosphorylation. The insulin receptor, for example, has
tyrosines that, once they are phosphorylated, act as binding sites for signaling proteins.
Likewise, phosphorylation can also prevent protein-protein interactions.
4. What is the enzymatic activity of a kinase and of a phosphatase?
A kinase is an enzyme that utilizes an ATP to transfer an organic phosphate to a molecule.
Different classes of kinases can phosphorylate different macromolecules like carbohydrates,
lipids, nucleic acids, and proteins. Protein kinases were the focus of this case as they are often
utilized in signaling pathways.
A phosphatase is an enzyme that removes a phosphate from a molecule.