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Biochemistry

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Carbohydrates

Question
15 out of 78
 

True statements about glucokinase is/are:



A Km value is higher than normal blood sugar

B Found in liver

C G-6P inhibits it

D Has both glucose 6 phosphatase and kinase activity

Ans. A + B A. Km value is higher than normal blood sugar, B. Found in liver

Difference between Hexokinase and glucokinase

Hexokinase

Glucokinase

- Phosphorylate any of the hexoses (non- specific),

more stable

- Found in all tissues

- Allosterically inhibited by Glucost-6-Phosphate

- Km is low, and high affinity for glucose

- No change with glucose feeding

- Inhibited by glucocorticoids and GH

- Main function is to make glucose available to tissues for oxidation at lower blood glucose level.

- Phosphorylate glucose only (specific)

- physiologically more labile

- Found only in liver and Pancreatic — Beta islet-cells

- Not inhibited by G-6-P

- Km is high and low affinity for glucose

- Increased after feeding of glucose after fasting

- Inhibited by Gluco-corticoids and GH

- Main function is to clear glucose from blood after meals and at blood levels> 100 mg/dL

In suilin this aeturty of Hexokinase II & IV

Glucokinase and Hexokinase phosphorylate Glucose to G-6-P with help of ATP and Mg++. This is an irreversible reaction. i.e. they cannot release glucose from G-6-P

a. Glucose is released from G-6-P (last step of glycogenolysis) by Glucose-6-Phosphatase (present in Liver and kidney but absent in muscles)

GLUT-2

a. Presents in Liver, pancreatic B-cells, small intestine

b. Not under direct control of Insulin

c. β-islet cells are freely permeable to glucose via GLUT-2 transporter.

d. Insulin, indirectly induces the glucokinase - this increases the phosphorylation of glucose - so that intracellular free glucose conc. stays low - facilitating the entry of glucose.

GLUT-4 present in Heart and skeletal muscles and Adipose tissue Insulin stimulated uptake of glucose.

Carbohydrates Flashcard List

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