I am a 40 yo going back to uni to get a biological science degree. You are so helpful in my life, not sure what I can do without you, such an inspiration. Honestly, when I'll grow up I want to be like you! Anyhow, thank you, you are brilliant!
At roughly 2:32 you mention that when blood glucose concentration is low, glucose is less likely to bind to glucokinase and will be more likely to bind to the hexokinases in brain / muscle cells. However, you said that the same hexokinase present in muscle / brain cells is also present in liver cells, so that statement seems contradictory. I've did some reading on Wikipedia, and from what I've read, the only enzyme present in liver cells is solely glucokinase, not hexokinase. This also makes sense logically since if both enzymes were present in liver cells, and there was low blood glucose concentration, then the hexokinase in liver cells and hexokinase in muscle / brain cells will have a "tug of war" on the glucose, which might be detrimental for the essential activities of the brain and muscle, which overrides the activity of the liver in times of scarce energy.
I'm no expert, but the wikipedia article in fact says that hexokinase I is present in all mammalian tissues. I'm also looking in the Lehninger, and it says that glucokinase (hexokinase 4) is the predominant isozyme in liver cells. As best I can find it never says it is the only one. Also from the Lehninger, "Hexokinase is present in all cells of all organisms. Hepatocytes also contain a form of Hexokinase called Hexokinase IV or glucokinase...". Seems to me that Hexokinase IV is the most common isozyme in hepatocytes but others (for sure Hexokinase I) must also be present in small amounts.
Another factor, not mentioned in the video, are the different glucose transporters (GLUT). The main transporters at play in your conundrum are the isoforms, GLUT1, GLUT2, and GLUT3. They each have different affinities (how fast they take up glucose) for glucose. In a starved state, glucose will be low, and the transporters with high affinities (GLUT1 and GLUT3) will "hog" the glucose. Every cell has some GLUT1 transporters, it is required to maintain low levels of basal glucose requirements, ie. you can still use those muscles to move. GLUT3 are found primarily in neurons and brain tissue, ie. you can still decide to and able to control movement to the sandwich. Where GLUT2 is a low affinity glucose transporter, meaning it is most active at high glucose concentrations. GLUT2 is the primary glucose transporter in the liver (though it will still have some GLUT1 for basal energy requirements in a low glucose state). As such, when glucose is low, the "tug of war" you mentioned will not be as pronounced because much of the glucose is not getting into the liver to be catalyzed by hexokinase in the liver. This is obviously an over simplification, but it I hope it helps to explain the contradiction.
YOU SAVED MY LIFE MY TIME AND MY TEARS
I am a 40 yo going back to uni to get a biological science degree.
You are so helpful in my life, not sure what I can do without you, such an inspiration.
Honestly, when I'll grow up I want to be like you!
Anyhow, thank you, you are brilliant!
Good luck with that, may the winds of fortune move you forward!
Thank you so much!!! I'm willing to pay you for graciously uploading the videos. You're a hundred times better than my professor.
You rock! Found the second half. Your videos are what gets my through this series! Thanks!
At roughly 2:32 you mention that when blood glucose concentration is low, glucose is less likely to bind to glucokinase and will be more likely to bind to the hexokinases in brain / muscle cells. However, you said that the same hexokinase present in muscle / brain cells is also present in liver cells, so that statement seems contradictory. I've did some reading on Wikipedia, and from what I've read, the only enzyme present in liver cells is solely glucokinase, not hexokinase. This also makes sense logically since if both enzymes were present in liver cells, and there was low blood glucose concentration, then the hexokinase in liver cells and hexokinase in muscle / brain cells will have a "tug of war" on the glucose, which might be detrimental for the essential activities of the brain and muscle, which overrides the activity of the liver in times of scarce energy.
I'm no expert, but the wikipedia article in fact says that hexokinase I is present in all mammalian tissues. I'm also looking in the Lehninger, and it says that glucokinase (hexokinase 4) is the predominant isozyme in liver cells. As best I can find it never says it is the only one. Also from the Lehninger, "Hexokinase is present in all cells of all organisms. Hepatocytes also contain a form of Hexokinase called Hexokinase IV or glucokinase...". Seems to me that Hexokinase IV is the most common isozyme in hepatocytes but others (for sure Hexokinase I) must also be present in small amounts.
Another factor, not mentioned in the video, are the different glucose transporters (GLUT). The main transporters at play in your conundrum are the isoforms, GLUT1, GLUT2, and GLUT3. They each have different affinities (how fast they take up glucose) for glucose. In a starved state, glucose will be low, and the transporters with high affinities (GLUT1 and GLUT3) will "hog" the glucose. Every cell has some GLUT1 transporters, it is required to maintain low levels of basal glucose requirements, ie. you can still use those muscles to move. GLUT3 are found primarily in neurons and brain tissue, ie. you can still decide to and able to control movement to the sandwich. Where GLUT2 is a low affinity glucose transporter, meaning it is most active at high glucose concentrations. GLUT2 is the primary glucose transporter in the liver (though it will still have some GLUT1 for basal energy requirements in a low glucose state). As such, when glucose is low, the "tug of war" you mentioned will not be as pronounced because much of the glucose is not getting into the liver to be catalyzed by hexokinase in the liver. This is obviously an over simplification, but it I hope it helps to explain the contradiction.
You never fail to impress me . Thank you sir
Amazing explanation 👏👏👏
OMG... I love you so much. huh.. i have been lost throughout this semester. you are a genius.
Awesome video!
I like ur teaching way very much! Do u have pictures of ur teaching tablets for ur lectures?
thank you for the awesome video!
Please do more video on Biochemistry!!!
amazing so can we say that glucokinase is the major in liver i mean that its concentration is higher than hexokinase in liver is that true
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