Glycolysis - General Flashcards
What are the two major functions of glycolysis?
- ATP generation
- Production of biomolecules
What are the three enzymes in glycolysis that are primarily regulated?
- Phosphofructokinase
- Hexokinase
- Pyruvate kinase
The liver does not need energy for contraction, and it actually uses fatty acids to obtain most of its energy. Why is glycolysis involved in the liver? What are the 3 things that can happen?
The liver maintains glucose levels in the blood.
The glucose is either:
- Stored as glycogen.
- Used to generate reducing power in the form of NADPH which is used for biosynthesis (pentose phosphate pathway).
- Converted via glycolysis into molecules that can serve as building blocks for other biomolecules.
How is phosphofructokinase regulated in muscle?
Inhibit: ATP and pH, with pH just enhancing the effect of ATP.
Activate: AMP
Why does AMP have a positive effect on PFK?
AMP competes with ATP for PFK’s binding site, but when it is bound, it does not inhibit the enzyme.
How is phosphofructokinase regulated in the liver?
Inhibit: ATP, pH, citrate (pyruvate metabolism)
Activate: fructose-2,6-bisphosphate
How does fructose-2,6-bisphosphate activate phosphofructokinase?
It increases substrate affinity, blunting the ATP effect.
What is feedforward stimulation in the context of glycolysis?
The acceleration of glycolysis during times of glucose abundance.
How is hexokinase regulated in muscle?
Inhibit: glucose-6-phosphate
How is the effect of G-6-P on hexokinase remedied? What does this in turn cause?
The first step of glycolysis is slowed to prevent total inhibition of hexokinase. This increases blood glucose levels and therefore insulin levels as well.
How is hexokinase regulated in the liver?
It isn’t. There is a special form called glucokinase which has a 50X higher Km for glucose than hexokinase, meaning that is is only activated at high glucose levels. Therefore, it is not inhibited by G-6-P.
How is pyruvate kinase regulated in muscle?
Inhibited: ATP, alanine
Activated: fructose-1,6-bisphosphate
Aside from glucose, what are the two other sugars that can enter glycolysis? Where do they enter?
Fructose and galactose. Fructose has two entry points but in the liver it enters around the aldolase step. Galactose enters in the second step.
What are the steps to get fructose into glycolysis through the liver?
- Fructose is phosphorylated into fructose-1-P by fructokinase.
- It is split into dihydroxyacetone phosphate and glyceraldehyde by a special aldolase.
- It is phosphorylated into glyceraldehyde-3-P by triose kinase.
Why does fructose pose a challenge to the body in glycolysis? What conditions can this cause?
It bypasses the key regulatory step resulting in the uncontrolled flow of metabolites, increasing pyruvate and Acetyl CoA levels in the body. This uncontrolled flux can lead to obesity, fatty liver and type 2 diabetes.
