hi let's talk about the enzyme hexokinase the enzyme hexokinase is the first enzyme of glycolysis which converts glucose into glucose 6 phosphate using ATP this enzyme also has the ability to phosphorate other hexo sugars like fr and Manos into their respective phosphorilated state hexokinase is a classical example of an induced fit model the induced fit model means whenever the substrate binds with the enzyme there's a change in the shape of the active site and the confirmation of the enzyme so when the substrate glucose and ATP binds with the enzyme the enzyme under goes a conformational change and because of this conformational change these two domains of the enzyme comes closer to one another once glucose and ATP are close to one another the hydroxy group which is at the sixth carbon atom of glucose reacts with the phosphate of ATP to form the final product now there's one more Point all of you must remember this reaction requires the presence of magnesium ions the Magnesium ions are positively charged the positive charge of magnesium ions Shields the negative charge on the oxygen attached with the phosphate of ATP this shielding allows the reaction between the phosphate and the hydroxy group attach with the sixth carbon atom of [Music] glucose if magnesium ions are absent then these negatively charge oxygen atoms will repel each other and this reaction will not occur so magnesium ions plays a very important role in this reaction now you should also know the difference between hexokinase and gluc the enzyme hexokinase is located in all the cells of the body whereas the enzyme glucokinase is located only in the liver cells hexokinase can act on all the hexo sugar whereas the enzyme glucokinase Works only on glucose the enzyme hexokinase has a low km value whereas glucokinase has a high km value now what I mean by low km value and high km value is that let's say these are our enzyme molecules and to this enzyme we add the substrate so km is a situation in which half of your enzyme molecule ules are occupied by the substrate if you see this carefully then the enzyme hexokinase over here is attached with a substrate whereas these are free enzyme molecules in a similar way the glucokinase over here is attached with the substrate and these are free glucokinase molecules now pay attention to this part this that you see in here this is a situation where 50% of the enzyme molecules are bound with the substrate forming the es complex so in case of hexokinase you need a little amount of substrate for 50% off s formation whereas in case of glucokinase you need a large amount of substrate to form 50% of the enzyme substrate complex hence we say the km value for hexokinase is low whereas the km value for glucokinase is high this also means that he exocin can function at very low substrate concentration whereas the enzyme glucokinase needs High substrate concentration to function