Biochemistry Exam 4
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During the oxidative phase in the pentose phosphate pathway, glucose 6-phosphate is converted to what molecules? (Give products, enzymes and requirements for each step).
- 1.) Glc-6-Phosphate + NADP ---> 6-phosphoglucono-delta-lactone + NADPH. (Enzyme is glc-6-P dehydrogenase).
- 2.) 6-phosphoglucono-delta-lactone ---> 6-phosphogluconate (Enzyme is Lactonase)
- 3.) 6-phosphogluconate + NADP---> ribulose 5-phosphate + NADPH (Enzyme is 6-phosphogluconate dehydrogenase)
True or false: Ribose 5- phosphate is isomerized by phophopentose epimerase to xylulose 5-phosphate?
FALSE: Ribulose 5-phosphate is isomerized to xylulose 5-phosphate by phosphopentose epimerase NOT ribose-5-p.
During the pentose phosphate pathway name the coupling of carbons added together for each step and what they give.
- 1.) Ribose 5 Phosphate + Xylulose -5-P <------> glyceraldehyde 3-phosphate + sedoheptulose 7-P (by transketolase)
- 2.) glyceraldehyde 3-phosphate + sedoheptulose 7-P <----> Fructose-6-P + Erythrose 4-P (by transaldolase)
- 3.) Fructose-6-P then enters the glycolytic metabolism pathways!
- 4.) Erythrose 4-P + xyulose 5-P <----> Fructose-6-P + Glyceraldehyde 3-P. (by transketolase)
How many fructose-6-p molecules and glyceraldehyde 3 molecules would it take to make the following number of ribose-5-phosphate: 3, 6, 10.
It takes 2 fructose molecules and 1 glyceraldehyde for 3 ribose-5-p molecules: 2 F-6-P &1 GAP; 4 F-6-P &2 GAP; can happen in multiple ways. At least 5 F-6-P and 2 GAP or more.
What is the regulatory enzyme in the pentose phosphate pathway and what is it mainly inhibited by?
The inhibitory enzyme is glucose-6-dehydrogenase. This molecule is allosterically inhibited by the concentration of NADP. Low levels of NADP (high energy state) inhibits glc-6-phosphate because there is no NADP to drive the oxidation steps of the pentose phosphate pathway forward. Also high concentrations of NADPH in liver cytoplasm competes in binding to this enzyme thereby preventing the oxidation of glucose-6-phosphate
Where does the pentose-phosphate pathway take place?
If the body needs more ribose 5-phosphate than NADPH what happens? When would this occur?
This would occur in a cell that israpidly dividing. Most of the glucose 6-phosphate is converted into fructose 6-phosphate and glyceraldehyde 3-phosphate by the glycolytic pathway. Then the nonoxidative pentose phosphate pathway takes 2 F-6-P and 1 GAP to form 3 Ribose-5-phosphates. (5 mol Glc --> 6 mol Ribose 5 phosphate)
If the needs for NADPH and ribose 5-P are balanced, what happens?
Glucose 6-Phosphate goes through mainly the oxidative phase of pentose phosphate pathway and stops at ribose sugars.
If the body needs much more NADPH than ribose 5-phosphate, what occurs? When would this happen?
Glucose-6-phosphate goes through the pentose phosphate pathway, all the way until the ribose molecules are combined (5+5 --> 3+7-->6+4-->4+5--> 6&3) and these final intermediates are given back into the gluconeogenic pathway to reform glucose-6-phosphate to start the cycle over. This occurs for example during Fatty Acid synthesis
If the body needs both NADPH and ATP, what happens?
The pentose phosphate pathway takes glucose-6-phosphate through the oxidative and nonoxidative steps, gives back the glycolytic intermediates which then proceed through normal glycolysis and emerge as pyruvate.
What enzyme causes hemolytic anemia and what are some symptoms?
Hemolytic anemia is caused by a deficiency in glucose 6-phosphate dehydrogenase. This deficiency is most acute in red blood cells and is inherited on the X chromasome. It lowers the amount of NADPH available to the body, which affects the reduction of glutathione to the sulfhydrl form by glutathione reductase. Causes meoglobin content of the blood to drop sharply, destruction of red blood cells and sometime death. Pamaquine can cause this in certain individuals.
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