Question

1. The intracellular concentration of glucose is approximately 1 mM. After consuming a candy bar, your blood glucose concentration is 1.5 g/L. a) Calculate the blood glucose concentration in molarity. b) Calculate the Gibbs free energy available for the transport of glucose into cells using the above concentrations. Assume T = 25 ˚C. c) Is the transport of glucose into the cell going to be spontaneous? Explain. d) Describe how the glucose transporter will move these glucose molecules across the membrane.

2. There are two types of mature lymphoblasts, Type I and Type II, with dissociation constants for insulin (Kd) of 0.46 nM and 2.1 nM respectively. Sketch a single Scatchard plot with a curve for each cell type. Which has a higher affinity for insulin and why?

3. A patient presents to the emergency room complaining of spells of dizziness and weakness, typically lasting ten minutes, which are increasing in frequency. These spells tend to come on after a large meal and seem to terminate by eating candy or drinking juice. As the emergency doctor, you order blood to be drawn and the glucose concentration tested. Your patient is found to have a blood glucose concentration of 1.1 mM, and after a 5-hr glucose tolerance test, her blood glucose was 2.6 mM. Your differential diagnosis consists of two possibilities: an insulinoma or insulin-dependent diabetes. a) Describe what is occurring in the case of an insulinoma and in insulin-dependent diabetes b) Which of these diagnoses best explain the patient’s symptoms and why?

4. Constriction of the bronchi and bronchioles of the lungs as a result of smooth muscle contraction gives rise to the symptoms of asthma. The muscle constriction can be reversed by increasing the concentration of cAMP. a) Explain how the ß-adrenergic agonist, albuterol, generates its therapeutic effects b) Some people experience side effects, such as nervousness and twitching, when taking albuterol. What is the metabolic reason for these side effects?

Answer 1

1. The intracellular concentration of glucose is approximately 1 mM. After consuming a candy bar, your blood glucose concentration is 1.5 g/L. a) Calculate the blood glucose concentration in molarity.

Glucose molar mass is 180.156 g/mol

Molarity of glucose is = 1.5/180.156 = 8.32 mM

b) Calculate the Gibbs free energy available for the transport of glucose into cells using the above concentrations. Assume T = 25 ˚C.

∆G = 2.303RTln(Cin/Cout).
Cout = 8.32 mM, Cin = 1 mM

∆G = 2.303 × 8.314 × 298.15 Log 1/8.32 = -5254.55 J/mol

c) Is the transport of glucose into the cell going to be spontaneous? Explain.

∆G is negative so it is spontaneous. It release energy to transport of glucose.

d) Describe how the glucose transporter will move these glucose molecules across the membrane.

In this case, facilitated diffusion would be required because glucose needs transport channels to allow it to pass through the lipid bilayer of the plasma membrane.

• Facilitated diffusion
  Transmembrane proteins create a water-filled pore through which ions and some small hydrophilic molecules can pass by diffusion. The channels can be opened (or closed) according to the needs of the cell.