A liver cell has two enzymes that add a phosphate group to glucose…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A liver cell has two enzymes that add a phosphate group to glucose. Hexokinase has mmol/L. Glucokinase has mmol/L. The glucose level in the blood is about 5.0 mmol/L between meals and rises to about 10 mmol/L after a meal.
- What share of its does each enzyme reach at 5.0 mmol/L?
- What share does glucokinase reach at 10 mmol/L?
- Why can glucokinase respond to a meal, when hexokinase cannot?
Need a reminder? The key ideaShow
. At the rate is half of . . On the double reciprocal plot the y-intercept is , the x-intercept is and the slope is .
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. At 5.0 mmol/L. Hexokinase: , which is 98 %. Glucokinase: , which is 33.3 %.
Step 2. At 10 mmol/L. Glucokinase: , which is 50 %.
Step 3. The meaning. Hexokinase is already almost saturated between meals. More glucose cannot make it work much faster. Glucokinase is far from saturation, so its rate climbs steeply as the blood glucose rises after a meal. It helps the liver to take up and store the extra glucose.
Answer: 98 %, 33.3 % and 50 %. Glucokinase has a large , so its rate follows the glucose level.
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