Half full sets the number

Science · Organisms & Life Processes · ages 19-20

Name ______________________ Date ____________

Kd is 10 nanomolar and the ligand concentration is 10 nanomolar. Type the filled fraction.
Answer: ______________
What is the dissociation constant, Kd?
- Half-full concentration
- Total receptor count on the cell
- Ligand arrival speed at the cell
A smaller dissociation constant means tighter binding.
Circle one: True False
Two ligands are plotted on the same axes. Which one binds tighter?
- The curve that flattens toward full earliest
- The curve with the higher top level reached
- The curve rising earlier to half full
Kd is 10 nanomolar and the ligand concentration is 90 nanomolar. Type the filled fraction.
Answer: ______________
A binding curve passes half full at 30 nanomolar. Type the Kd in nanomolar.
Answer: ______________
Sam says that at ligand equals Kd, 90 percent of receptors are filled. What is wrong?
- 90 percent, since Kd is defined as nearly full
- 10 percent, since Kd means nearly empty
- 50 percent, since Kd means exactly half full
Raising the ligand from 10 times Kd to 20 times Kd doubles occupancy. True or false?
Circle one: True False

Answer key

For grown-ups. Fold this page away before handing over the rest.

0.5 · Filled equals ligand divided by Kd plus ligand, so 10 divided by 20 is 0.5.
Half-full concentration · Kd is read as the half-full concentration.
True · Half occupancy comes sooner for a tighter grip, which is the smaller Kd.
The curve rising earlier to half full · Earlier half-full means a smaller Kd and tighter binding.
0.9 · 90 divided by 10 plus 90 is 90 divided by 100, or 0.9.
30 · Kd is the concentration at half full, so the Kd is 30 nanomolar.
50 percent, since Kd means exactly half full · Kd is defined as the half-full concentration, so Sam overread it.
False · Near the flat top it only moves about 0.91 to 0.95.