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Biochemistry Video 19


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What does lactose come from?
Dairy products
What is lactose converted to and what enzyme does this?
Lactose is converted to glucose and galactose by LACTASE
In what type of people is lactase deficiency common?
Asian and people of African decsent
Which steps of glycolysis are irreversible?
Glucokinase/hexokinase⬦⬦⬦⬦ PFK-1 ⬦.Pryuvate kinase
Where does the conversion f lactose to glucose and galactose take place?
Lactase is in the intestine and thus it takes place in the intestine
What is the first step in the metabolism of galactose?
As with other sugars, it must be phosphorylated in order to keep in inside the cell. This is done by GALACTOKINASE and the product is galactose 1-P
After galactose is converted to galactose 1-P, what is the next step in galactose metabolism?
Galactose 1-P is converted to glucose 1-P by GAL 1-p uridyl transferase (it is one of only 2 significant enzymes in galactose metabolism, just remember that this is the one other than galactokinase)
What happens to glucose 1-P?
Glucose 1-P is converted to Glucose 6-P and go through glycolysis or it can for glycogen stores
In which enzymes of galactose metabolism do deficiencies exist?
Deficiencies exist in galactokinase and Ga1-P uridyl transferase⬦⬦both of the important enzymes of galactose metabolism
What happens in a galactokinase deficiency?
Galactose does not get phosphorylated and trapped in the cell and thus it accumulates in the blood and thus will cause galactosurea and cataracts due to lens swelling
What enzyme is responsible for the buildup of galactose products in the lens?
Aldose reductase
What is the product of aldose reductase action on galactose?
Galactitol concentration build up in the lens of the eye and causes swelling and cataracts
Why do diabetics get cataracts?
Diabetics have increased glucose in the blood, and in the same way that it converts galactose to galactitol, it also converts glucose to sorbitol
What is the clinical presentation of someone with a deficiency in Gal 1P uridyl transferase?
They will also have cataracts, but because they are able to form galactose 1-P the galactose will be able to accumulate in the cells and thus there will be cell damage resulting in many more and severe symptoms. Symptoms in addition to cataracts include liver damage leading to hyperbilirubinemia, mental retardation, lethargy and vomiting and diarrhea following lactose ingestion
What is the treatment for someone with a galactose metabolism enzyme deficiency?
Totally restrict any products containing glactose. Therefore totally restrict all dairy products.
What is regular table sugar?
What is administered during hypoglycemia and what is the result?
Galactose is administered during hypoglycemia and this induces an increase in blood glucose.
Where does the breakdown of sucrose occur and what does it produce?
The breakdown occurs by the enzyme sucrase which is in the intesting. The breakdown of sucrose results in glucose and fructose
What is the first step in the metabolism of fructose?
As with other sugars it is the conversion of fructose to fructose 1P by fructokinase
What are the main cells that fructose is used in?
Liver and kidney cells
What happens to fructose 1P?
It is converted to intermediates of glycolysis, DHAP and Glyceraldehyde by ALDOLASE B (glyceraldehydes is then phosphorylated to glyceraldehydes 3P)
What Happens to glyceraldehyde?
It is phosphorlyated to glyceraldehydes 3P and can be used in glycolysis, glycogenesis, or gluconeogenesis
How is a fructokinase difieiency differentiated from galactokinase deficiency?
In fructokinase deficiency, there are no cataracts .... Because fructokinase can be phosphorylated by other enzymes it is a very benign disease
What happens in Aldolase B deficiency?
There will be a buildup of fructose-1P in the cells and thus the cells will swell and be damaged. The main symptoms will be liver damage resulting in hyperbilirubinemia/jaundice and renal proximal tubule damage resembling Fanconi syndrome. There will also be failure to thrive, lethargy, and vomiting
What is the treatment for aldolase B deficiency?
Eliminate sources of fructose in the diet
What enzyme converts pyruvate to Acetyl CoA?
Pyruvate dehydrogenase
What happens to Acetyl-CoA?
If there is enough energy already, it will turn to fatty acids. If energy is needed, it will go through Krebs cycle and the ETC and produce ATP
What is the difference in the location between alyceraldehyde 3P dehydrogenase and PDH?
Glyceraldehyde 3P dehydrogenase is in the cytoplasm which PDH is in the mitochondria
What regulates PDH?
Globally insulin regulates PDH, and thus PDH will only work when activated by insulin ..... Locally, Acetyl CoA will provide negative feedback to the pyruvate dehydrogenase.
What does the dehydrogenase indicate about the PDH?
It will give its hydrogen to NAD to form NADH
What are the cofactors needed for the action of PDH?
Tender Love and Care For Nance....T:Thiamine....L: Lipoic Acid....C: Coenzyme A....F: FAD....N: NAD
What is the precursor of Coenzyme A?
Pantothenate (pantothenic acid)
What vitamin does FAD come from?
What vitamin does NAD come from?
In what people is thiamine deficiency seen?
What disease is associated with thiamine deficiency and what is the mechanism?
Wernicke Korsakoff Syndrome is associated with thiamine defiecency. The is a deficiency because alcohol interferes with thiamine absorption from the intestine
Why does thiamine deficiency have such strong neuron symptoms?
Thiamine is a cofactor of PDH, and without PDH the neuron tissue cannot extract ATP form the TCA cycle and Electron transport chain
What is important in the treatment of an alcoholic with hypoglycemia?
You must first administer thiamine before administering glucose so that the PDH can work and utilize the administered glucose
Does Krebs cycle and TCA occur during the well fed or postabsorptive state?
Unlike both glycolysis and PDH, Acetyl CoA will go through Krebs cycle and ETC at all times except in Red blood cells, which do not possess mitochondria
What controls the action of Krebs cycle and the ETC?
They are only under local control. If there is a lot of ATP they will slow down and let their intermediates go to other pathways. Whereas if the cell needs more ATP they will speed up
What are the sources of Acetyl CoA as a substrate for the Krebs cycle?
Pyruvate via glucose and amino acids, fatty acids, Ketones, and alcohol
Draw the citric acid cycle.
What is another name for succinate dehydrogenase?
Complex 2 of the electron transport chain
What is special about the reactions of the Krebs cycle involving any form of the word succinate?
The do not for NADH.
What is the name of the enzyme that detects the anoumt of NADH and thus slows down or speeds up the Krebs cycle?
Isocitrate dehydrogenase
If Acetyl CoA is produced in the mitochondria, how does it get out.
It cannot get out directly. It changes to citrate (part of krebs cycle) which goes through the citrate shuttle to exit the mitochondria
Which intermediates of the Krebs cycle can be used in other pathways?....What are these pathways?
Citrate = fatty acid synthesis....Succinyl CoA = Hene synthesis....Fumarate = Urea cycle....Malate = gluconeogenesis
Name the reactions which produce NADH.
Glyceraldehydes 3P dehydrogenase....Pyruvate dehydrogenase....Isocitrate dehydrogenase....Alpha ketogluterate dehydrogenase....Malate dehydrogenase
Where does the electron transport chain take place?
In the inner mitochondrial membrane

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