Highlights Glycolysis III Flashcards
The phenomenon of redox balancing is important for glycolysis. What does Redox balancing relate to?
The phenomenon of redox balancing is important for glycolysis. Redox balancing relates to the relative amount of NAD+ and NADH in the cell. Remember that reaction 6 is very sensitive to the ratio of NAD+/NADH. Redox balancing involves pyruvate in all cells.
Pyruvate has three separate fates, depending on conditions and the cell type. What are they?
Pyruvate has three separate fates, depending on conditions and the cell type.
When oxygen is present, there is plenty of NAD+, so aerobic cells convert pyruvate to acetyl-CoA for oxidation in the citric acid cycle.
When oxygen is absent, NAD+ levels can go down, so to prevent that from happening, pyruvate is converted to either lactate (animals) or ethanol (bacteria/yeast).
Either of these last two conversions REQUIRES NADH and produces NAD+. NAD+ made in this way can be used to keep reaction 6 of glycolysis going.
How does anaerobic conversion of NADH to NAD+ compare to the aerobic conversion?
Anaerobic conversion of NADH to NAD+ provide MUCH LESS ATP energy to cells than when oxygen is present.
Anaerobic metabolism of glucose generates only 2 ATPs per glucose, whereas aerobic metabolism of glucose generates 38 ATPs per glucose.
Other sugars than glucose can be metabolized by glycolysis, if ___.
Other sugars than glucose can be metabolized by glycolysis, if they are converted to intermediates of glycolysis.
Galactose can enter glycolysis by ___
Galactose can enter glycolysis by being converted to galactose-1phosphate followed by converstion (ultimately) to glucose-1-phosphate and subsequently to glucose-6-phosphate, which is a glycolysis intermediate.
What does deficiency of the enzyme lactase lead to?
Deficiency of the enzyme lactase leads to lactose intolerance. Lactase is necessary to break lactose down to glucose and galactose.
Why is entry of fructose to the glycolysis cycle may be problematic in high carb diets
Fructose can be converted to F6P by hexokinase. Fructose can also be converted to fructose-1-phosphate (F1P) by fructokinase. Conversion of F1P to glyceraldehyde and DHAP allows fructose to be metabolized by glycolysis without being controlled by PFK. Ingestion of a lot of fructose (via high fructose corn syrup in many foods) may be a factor in obesity.
Regulation of glycolysis is controlled by three enzymes. What are they?
Regulation of glycolysis is controlled by three enzymes - hexokinase, PFK, and pyruvate kinase. Hexokinase’s regulation is a bit complicated and is controlled partly by availability of substrate.
PFK is very unusual in being negatively regulated by a molecule (ATP) that is also a substrate. How is this possible?
This is possible because the enzyme has an allosteric binding site for ATP in addition to the substrate binding site and the Km for the allosteric site is higher than the substrate binding site.
