Chapter 14. Chapter 14

Problem-Solving Video Assessment

true

false

Chapter 14 Problem-Solving Video Assessment

You have discovered a new cell-surface receptor (receptorX) that you believe binds to either insulin or epidermal growth factor (EGF). To differentiate between the two ligands, you radiolabel each ligand to a specific activity of 4 x 10⁷ cpm per micromole. You then perform ligand–receptorX binding experiments in your cell line and generate the following counts of cell-bound radioactivity:

	insulin	EGF
Radioactive ligand alone	5563 cpm	6012 cpm
Radioactive ligand + 1000-fold excess unlabeled ligand	237 cpm	5874 cpm

Table

1.

Given this data, which of the following statements is correct? Assume that in your cell line, receptorX is the only receptor present for either ligand.

Insulin is the preferred ligand for receptorX because it displays higher total binding.

EGF is the preferred ligand for receptorX because it displays higher total binding.

EGF is the preferred ligand for receptorX because it displays lower nonspecific binding.

Insulin is the preferred ligand for receptorX because it displays higher specific binding.

EGF is the preferred ligand for receptorX because it displays higher specific binding.

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

2.

You determine that the specific binding for the preferred ligand is 7.2 x 10⁶ cpm per milligram of membrane protein. What is the concentration of ligand bound per cell? Assume that there are 10¹⁵ cells per milligram of membrane protein.

1.8 x 10^-16 μmole/cell

5.6 x 10^-15 μmole/cell

7.2 x 10^-9 μmole/cell

0.29 μmole/cell

1.8 x 10¹⁴ μmole/cell

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

3.

Assuming that one ligand binds per receptor, how many receptorX molecules are present per cell?

1.1 x 10¹⁴ molecules

4.3 x 10⁹ molecules

1.1 x 10⁸ molecules

3371 molecules

108 molecules

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

4.

You discover that each ligand actually binds two receptorX molecules simultaneously. This ligand–receptor interaction leads to cross-phosphorylation of the receptorX dimer, inducing a downstream signaling cascade. In light of your new discovery, how many receptorX molecules must be present per cell?

54 molecules

108 molecules

216 molecules

1685 molecules

6742 molecules

_feedback_correct: Correct. _feedback_incorrect: Incorrect.

Activity results are being submitted...

Chapter 14. Chapter 14

Introduction

1.

2.

3.

4.