Glycolysis

a second question is then posed.

After this experiment, mice are grown that have a mutant fructose-1,6-biphosphatase that doesn't recognize fructose-2,6-bisphosphate. What effect will the mutation have on the glucose metabolism of the mice, and what can be deduced about the behavior or outer appearance of the mice?

In the absence of oxygen, the only option for skeletal muscles to generate ATP is glycolysis. Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, CH3COCOO? + H+. Glycolysis does not require oxygen to function, so it consistently works and produces ATP. The phenomenon you're seeing after you add oxygenated blood is called oxygen debt. Animals often show elevated rates of oxygen consumption long after the cessation of exercise to restore the body to a resting state. When this is accomplished, the body then maintains a steady rate, as you observed in your experiment.

In Fructose 1,6-bisphosphatase deficiency, there is not enough fructose bisphosphatase for gluconeogenesis (generation of glucose) to occur correctly. So sugars, including lactate, are not chemically converting into glucose; however, glycolysis (the break-down of glucose) will still work in the presence of glucose, as it does not use this enzyme. This enzyme also permits endogenous glucose production from gluconeogenic amino acids (eg, alanine and glycine) and glycerol. Without these amino acids, you can kind of make up what will happen to the mouse (i.e. decreased muscle production).

Without effective gluconeogenesis (GNG), hypoglycaemia will set in after about 12 hours. This is the time when liver glycogen stores have been exhausted, and the body has to rely on GNG. When given a dose of glucagon (which would normally increase blood glucose) nothing will happen, as stores are depleted and GNG doesn't work. (In fact, the patient would already have high glucagon levels.)

There is no problem with the metabolism of glucose or galactose, but fructose and glycerol cannot be used as fuels. If fructose or glycerol are given, there will be a build up of phosphorylated three-carbon sugars. This leads to phosphate depletion within the cells, and also in the blood. Without phosphate, ATP cannot be made, and many cell processes cannot occur.

High levels of glucagon will tend to release fatty acids from adipose tissue, and this will combine with glycerol that cannot be used in the liver, to make triacylglycerides causing a fatty liver.
As three carbon molecules cannot be used to make glucose, they will instead be made into pyruvate and lactate. These acids cause a drop in the pH of the blood (a metabolic acidosis). Acetyl CoA (acetyl co-enzyme A) will also build up, leading to the creation of ketone bodies.

in fructose 1,6-bisphosphate deficiency.. fermentation can't occur ? or lactate can't be converted back to pyruvate ? or both or neither ? .. just curious

No fermentation still occurs because this enzyme is not directly associated with glycolysis. Pyruvate is still produced via glycolosys, which is chemically converted into lactic acid. In the cori cycle, lactic acid is converted back to pyruvate and pyruvate undergoes gluconeogenesis where it becomes glyceraldhye-3-phosphate -> glygeraldehdye-3-phosphate becomes fructose-1,6-phosphate but you get a buildup of fructose-1,6-phosphate since no fructose 1,6-bisphosphatase enzyme exists.

ok thx

you're welcome

Wish we had more members like karim89  ones that actually want to learn 

haha .. well this particular subject ( all what has to do with cell respiration ) interests me for some reason more than other things.. but biology in general is definitely not a major that a person can get really good at if he studies it just to pass tests and exams