-Mg2 shields the negative charges of two of the phosphate oxygen atoms of ATP.-Mg2 makes the γ (terminal) phosphorus atom of ATP more accessible to nucleophilic attack by a glucose -OH group.
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In the 6th step of glycolysis, how is the high-energy compound 1,3-bisphosphoglycerate produced in the glyceraldehyde 3-phosphate dehydrogenase reaction, which is close to equilibrium?
-The oxidation of the aldehyde is strongly exergonic. -The thioester intermediate is a high-energy compound that “traps” some energy from the oxidation of glyceraldehyde 3-phosphate and enables phosphorylation.
-increased levels of frutose 2,6-biphosphate in mammals -activation of PFK-2 (phosphofructokinase-2 in mammals) -increased levels of ADP
the phosphofrictokinase reaction (PFK). it is the slowest reaction in glycolysis and is regulated by several molecules
which step of the glycolysis pathway is the control point? what negative effectors inhibit this enzyme and what positive effectors activate this enzyme?
What would be the limiting factor for ATP production by glycolysis in a strenuously-exercising muscle that lacks lactate dehydrogenase?
Lactate formed by the muscle (by fermentation) is transported through the blood to the liver where it is converted by glucose through gluconeogenesis. Purpose: scavenging lactate; detoxifying muscle cells by removing lactate > converting to glucose; liver takes on part of the metabolic burden from the muscle
An allosteric enzyme usually has two forms, active and inactive. If a competitive inhibitor (NOT an allosteric inhibitor) is added to a solution containing this enzyme, the ratio of active form of this enzyme to inactive form actually increases. Explain how this can happen.
An allosteric enzyme has two forms: an active form is maintained when the active site is occupied, and an inactive form is maintained when the regulatory site is occupied by an allosteric inhibitor. A non-allosteric competitive inhibitor competes against the substrate for the same active site, thus it actually helps maintain the “active” form.
What are the two most important parameters in enzyme kinetics? Which of these two is likely affected by competitive inhibition?
Vmax and Km are the two most important parameters in enzyme kinetics. Km is likely affected by competitive inhibition while Vmax is NOT likely to be affected (Vmax is the V0 when
is very high, thus S can out compete the inhibitor)
Gluconeogenesis can be considered as the reversal of glycolysis except two important steps. What are these two steps?
1) the conversion between F6P and F1,6BP (F6P to F1,6BP catalyzed by PFK for glycolysis and F1,6BP to F6P catalyzed by FBPase for gluconeogenesis 2) the conversion between PEP (phosphoenolpyruvate) and pyruvate (PEP to pyruvate catalyzed by pyruvate kinase and pyruvate to PEP in two steps
If you feed the cell with a 14C labeled glucose labeled with 14C at the fourth carbon. When do you expect this 14C is released as 14CO2? Do you expect any of the Citric Acid Cycle intermediates to be labeled? Explain your answer.
The 4th C on a glucose molecule will become the 1st C on a glyceraldehyde-3- phosphate molecule when the six-C fructose 1,6 BP is split into two C3 molecules (the lower half of the fructose, i.e., #4, #5 and #6 C, becomes glyceraldehyde 3-phosphate). Thus, the 4th C on glucose becomes the 1st C on the pyruvate molecule, the ending point of glycolysis. This 1st C is released as CO2 when pyruvate is oxidized to become acetyl CoA. Thus, acetyl CoA is not labeled, hence no citric acid cycle intermediates will be labeled.
Epinephrine triggers the synthesis of cAMP, which activates PKA (see signaling pathway of epinephrine). As shown in the diagram above, PKA phosphorylates PFK2-FBPase2 knocking out PFK2 activity, hence reducing the level of F2,6BP, leading to slowdown in glycolysis and enhancement in gluconeogenesis for the synthesis of glucose. F2,6BP is a regulatory molecule activating PFK, thus speeding up glycolysis, and also reducing the inhibitory effect of ATP on PFK. F2,6BP also inhibits the activity of fructose 1,6-bisphosphatase, a key enzyme in gluconeogenesis.
What are the unique features of phosphofructokinase 2 (PFK2) and fructose 2,6 bisphosphate phosphatase 2 (FBPase2).
These are two opposing enzymatic activities located in two different domains in the same polypeptide chain. PFK2 is responsible for the synthesis of F2,6BP, while FBPase2 catalyzes the hydrolysis of F2,6BP to F6P. Phosphorylation and de-phosphorylation regulates the differential activities of these two enzymes (as shown in the diagram above).
Which step of gluconeogenesis is the main negative control point? (Use the numbering system in the image at right.)
Fructose is converted into glycolytic pathways by fructokinase by 1. phosphorylation of fructose into fructose 1 phosphate by fructokinase2. fructose 1 phosphate is then split into glyceraldehyde and hydroxyl phosphate by fructose 1 phosphate aldolaseIn adipose tissue fructose can be phosphorylated to the glycolytic intermediate fructose 6-phosphate by hexokinase
excessive fructose can lead to pathological condition because the actions of fructokinase and triose kinase bypass the phosphofructokinase regulatory step. The glyceraldehyde are processed to pyruvate and eventually to acetylCoA IS converted to fatty acids which can result in obesity causing fat t accumulate in the liver.
1. Galactose——>galatose 1 phosphate (galactokinase+ATP)2. Galactose 1-phosphate +UDG-Glucose—->UDP Galactose+ glucose 1-Phosphate (galactose 1-phosphate uridyl transferase)3. UDP-galactose——>UDP glucose (UDP-galactose 4 epimerase) epimerase inverts the hydroxyl group to carbon 4 to glucose4. Glucose 1-phosphate——->glucose 6 phosphate (phosphoglucomutase)
In glycolysis name the three enzymes that catalyze the irreversible rxns and as a result are control sites in glycolysis?
Phosphofructokinase is an allosteric enzyme where high levels of ATP allosterically hinder it. AMP(NOT ADP) binds competitively to its active site but when bound does not inhibit the enzyme. The activity of te enzyme increases when the ATP/AMP ratio is lowered. Low pH also inhibits the enzyme