Question

Brain cells, which depend on glucose for energy, use the glucose transporter GLUT3, which has a Km of 1.5mM. Liver cells, which store glucose (as glycogen) after a meal and release glucose between meals, use the glucose transporter GLUT2, which has a Km of 15mM. Calculate the rate (as a % of Vmax) of glucose uptake in brain cells and in liver cells at circulated glucose concentrations of 3mM (starvation), 5 mM (normal levels), and 7mM (after a carbohydrate-rich meal). Use this rearranged M-M equation.

Answer 1

Step-by-step explanation:

Given that:

The brain cell which uses glucose transporter GLUT3 Km = 1.5 mM

The liver cell which stores glucose GLUT2 Km = 15 mM

The objective is to calculate the rate (as % of Vmax) of glucose uptake in brain cells and liver cells under starvation conditions.

Using the M-M equation i.e Michaelis- Menten equation;

`Rate = (V_(max)* [S])/([S]+K_m)`

By rearrangement

`(Rate)/(V_(max))= ([S])/([S]+K_m)`

where;

`V_(max)` = maximum velocity of a reaction

Thus; the rate as a % of Vmax of glucose uptake in brain cells is calculated as:

`(Rate)/(V_(max))= ([3 \ mM])/([3 \ mM]+1.5 \ mM)`

`(Rate)/(V_(max))= (3 \ mM)/(4.5 \ mM)`

`(Rate)/(V_(max))=0.667`

`(Rate)/(V_(max))=66.7 \%`

the rate as a % of Vmax of glucose uptake in liver cells is calculated as:

`(Rate)/(V_(max))= ([3 \ mM])/([3 \ mM]+15 \ mM)`

`(Rate)/(V_(max))= (3 \ mM)/(18 \ mM)`

`(Rate)/(V_(max))=0.166`

`(Rate)/(V_(max))=17 \%`

Thus, the uptake is larger brain cells due to the fact that the brain cells GLUT3 have higher tendency to attract glucose.