Chapter 16: Glycolysis Flashcards
Intermediate Mneumonic:
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Food
Gentlemen
Dine
Girls
Boys
Prefer to
Pick up
Pepperoni
Pizza
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1,6-Bisphosphate
Glyceraldehyde-3-phosphate
Dihydroxyacetone phosphate
Glyceraldehyde-3-phosphate
1,3-Bisphosphoglycerate
3-phosphoglycerate
2-phosphoglycerate
phosphoenolpyruvate
pyruvate
Enzyme Mneumonic:
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The Training
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Hexokinase
Phosphoglucose isomerase
PFK-1
Aldolase
Triose phosphate isomerase
Glyceraldehyde-3-phosphate dehydrogenase
Phosphoglycerate kinase
Phosphoglycerate mutase
Enolase
Pyruvate kinase
How does galactose enter glycolysis?
Galactose will go into glycolysis through glucose-6-phosphate. It does this by first adding a phosphate to galactose and pairing it with UDP-glucose. Then the groups are transfered with transferase so it is UDP-galactose and glucose-1-phosphate. The last step is a mutase step moving the phosphate to the 6th carbon.
-It is very important that it go in through glucose-6-phosphate because this means the glucose molecule is stuck in the cell and cannot be transported back out of the cell like just glucose could.
-The disaccharide lactose is made of galactose and glucose.
How does fructose enter glycolysis?
-Fructose can enter the glycolysis cycle two ways depending on where it is located at the time.
Muscles: The fructose can enter glycolysis through Fructose-6-phosphate with just an addition of a phosphate group.
Liver: The liver is more complicated. The fructose will have a phosphate group added but at the 1 carbon to produce F-1-phosphate. It will then go through an aldol cleavage to produce glyceraldehyde (not GAP) and DHAP. DHAP will isomerize by Triose isomerase phosphate to produce GAP. The glyceraldehyde will then have a phosphate group added to produce GAP. Both GAP molecules will enter the glycolysis cycle at GAP.
-Sucrose is a disaccharide made of fructose and glucose.
Why do high levels of fructose in the diet cause fatty liver?
When excess fructose is in the diet less is used for energy so it has to be stored or made into something else. Storage in glycogen or the liver can go thorough lipogenesis to create fats. This is where fat around the liver and stomach come into play.
Which enzymes control glycolysis?
Hexokinase, Phosphofructokinase and pyruvate kinase. These enzymes are the irreversible steps of glycolysis. The main control point is phosphofructokinase and pyruvate kinase though.
Which enzymes control gluconeogenesis?
Pyruvate carboxylase, Phosphoenolpyruvate carboxykinase, Fructose 1,6-bisphosphatase and glucose-6-phosphatase
What are the effects of the regulators of the enzymes at the control points?
Hexokinase- the intermediate glucose-6-phosphate inhibits hexokinase when there a high levels of it.
Phosphofructokinase- AMP activates this enzyme. (AMP suggest that there is very low energy/no ATP so we need to make energy so glycolysis will proceed).
-ATP inhibits this enzyme. In high energy states there is no need to continue making energy so glycolysis will be inhibited and stop.
-Citrate inhibits this enzyme. High levels of citrate mean that the citric acid cycle is backed up and there are too many citrate molecules so to catch back up glycolysis is inhibited and stopped.
Pyruvate kinase- ATP inhibits this enzyme. (Too much energy so no need to make energy through glycolysis).
-Fructose 1,6-bisphosphate activates this enzyme. This intermediate is before PEP so an increase before pyruvate kinase will push the reaction forward to go through glycolysis.
What are the steps of gluconeogenesis?
The same as glycolysis except for the intermediate oxaloacetate (before pyruvate) and the enzymes glucose-6-phosphatase, fructose 1,6-bisphosphatase, PEP carboxykinase and pyruvate carboxylase.
Descirbe the Cori Cycle. Why is it useful?
The Cori Cycle has to do with lactic acid. It starts in the muscle cell where glycolysis is running. pyruvate is made and then lactate when there is overabundance (working out). The lactate is sent through the bloodstream to the liver where it is taken back to glucose through gluconeogenesis.
This cycle is useful because when there is high need for energy in the muscle cells the lactate can be utilized and travel from the muscle to the liver to create more glucose and then go back to the muscle cells.
Describe the relationship between glycolytic intermediates and hemoglobin binding.
Glycolysis creates 3-phosphoglycerate which can be used to react with a separate enzyme to form 2,3 bisphosphoglycerate. This molecule decreases O2 binding to hemoglobin.
How does Fructose-2,6-bisphosphate regulate both glycolysis and gluconeogenesis?
It is an allosteric regulator that also activates phosphofructokinase in glycolysis and inhibits fructose 1,6- bisphosphatase in gluconeogenesis.
This feature is unique because it activates the forward reaction while inhibiting the reverse reaction. This prevents substrate cycling and waste of ATP.
What is the tandem enzyme (PFK-2/FBPase-2) and which hormones regulate it and how?
It catalyzes the reaction of fructose-6-phosphate to produce fructose-2,6-bisphosphate. ATP and F-6-P combine in PFK-2 to make F2,6BP and F2,6BP can have a phosphate removed to form F-6-P again in the FBPase-2. FBPase-2 and PFK-2 are on the same polypeptide chain.
Low blood glucose levels:
-PFK-2 is active
-glucagon is stimulated
-FBPase-2 is phosphorylated
-Lowers F2,6BP and sugars rise
High blood glucose levels:
-FBPase-2 is active
-insulin is stimulated
-PFK-2 is phosphorylated
-Raises F2,6BP and sugars lower.
