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Notes to Instructors
Chapter 11 Cell Communication
What is the focus of this activity?
Most students understand that external signals interact with receptors in cells and that the
What is the particular activity designed to do?
Activity 11.1 How are chemical signals translated into cellular responses?
In this activity, students model and compare the functions of a G-protein receptor system
What misconceptions or difficulties can this activity reveal?
Activity 11.1
Modeling the G-protein receptor system and the tyrosine-kinase receptor system does not
reveal misconceptions; rather, it tends to fill in missing information. Most students at the
62 Notes to Instructors
Answers
Activity 11.1 How are chemical signals translated into
cellular responses?
Chapter 11 in Campbell Biology, 9th edition, describes at least four kinds of signal
receptors. Three of these—G-protein-linked receptors, tyrosine-kinase receptors, and
ion-channel receptors—are plasma membrane proteins. Protein receptors found in the
G-Protein Receptor System Tyrosine-Kinase Receptor System
signal protein signal protein
G-protein-linked receptor tyrosine-kinase receptor
plasma membrane plasma membrane
inactive and active G protein inactive and active relay proteins
Use your models to show how signal reception by each of the systems can lead to the
release of Ca+from the endoplasmic reticulum. Demonstrate and explain your models to
another student group or to your instructor.
Then use your models to answer the questions on the next page.
Activity 11.1 63
1. How are these two systems similar? Consider both structural similarities and
similarities in how the systems function.
In both systems, the receptor proteins are bound in the cell’s membrane. Binding of
2. How are the two systems different? Consider both structural differences and
differences in how the systems function.
The G-protein-linked receptor protein is a single unit that becomes functional when
activated by its signal molecule. Two tyrosine-kinase receptor proteins must be
3. Both systems can generate elaborate multistep signal-transduction pathways. These
pathways can greatly amplify the cell’s response to a signal; the more steps in the
pathway, the greater the amplification of the signal. Explain how this amplification
can occur. (Review Figure 11.16, page 220, in Campbell Biology, 9th edition.)
In a signal-transduction pathway, each activated enzyme or second messenger has
64 Activity 11.1
Activity 11.1 65
11.1 Test Your Understanding
Humans have the ability to detect and recognize many different aromatic chemicals by
smell. Many of these chemicals are present in concentrations less than 1 ppm (part per
million) in the air. For example, the majority of humans can detect and recognize chlorine
at a concentration of about 0.3 ppm.
a. What characteristics of olfactory (smell) receptors would you look for or propose to
explain this ability?
Proposing that olfactory receptors are G-coupled protein receptors would be
b. Dogs are known to have a much better sense of smell than humans. Given this, what
differences may exist in their olfactory system (as compared to humans)?
Here students could propose either greater expression of receptors in the olfactory
