41 - the most crucial regulators of the citric acid cycle are its substrates , acetyl co A and oxaloacetate , and its product , NADH .
the above statement is true .
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42 - which enzyme of the citric acid cycle is very similar structurally and mechanistically to lactate dehydrogenase and alcohol dehydrogenase ?
a- alpha ketoglutarate dehydrogenase
b- succinate dehydrogenase
c- NAD + dependent isocitrate dehydrogenase
d- malate dehydrogenase
answer is d .
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43 - the thiamine pyrophosphate ( TPP ) a cofactor is bound to E1 and decarboxylates pyruvate , yielding a hydroxyethyl TPP carbon ion .
the above statement is true .
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44 - several biosynthetic pathways use citric acid cycle intermediates as starting material for anabolic reactions .
the above statement is true .
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45 - lipoamide consists of lipoic acid covalently joined to the epsilon - amino group of a lysine residue via an amide bond .
the above statement is true .
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46 - how is flux through out the citric acid controlled ?
a- primarily by control of citrate synthase
b- primarily by control of isocitrate dehydrogenase
c- primarily by control of alpha ketoglutarate dehydrogenase
d- at many points , including all the above
answer is d .
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47 - alpha ketoglutarate dehydrogenase is a multienzyme complex containing alpha ketoglutarate dehydrogenase ( E 1 ) , dihydro lipoyl trans succinylase ( E2 ) and dihydro lipoyl dehydrogenase .
the above statement is true .
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48 - in pyruvate dehydrogenase which cofactor is used to decarboxylate pyruvate?
a- TPP
b- lipoic acid
c- co A
d- FAD
the answer is a .
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49 - describe the regulatio of the conversion of isocitrate to alpha keto glutarate ?
a- calcium and ADP stimulate , NADH AND ATP inhibit .
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50 - Isocitrate lyase and malate sythase occur in both plants and animals .
the above statement is false . these enzymes occur only in plants .
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51 - acetyl co A is formed from pyruvate through oxidative decarboxylation by a multienzyme complex named ?
answer is pyruvate dehydrogenase .
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52 - which three compounds associated with the citric acid cycle inhibit their own synthesis ?
answer is acetyl co A , citrate and succinyl co A .
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53 - the tight coupling of oxygen consumption , NADH reoxidation and ATP production in the citric acid cycle requires regulation by feedback mechanisms that coordinate NADH Production with energy expenditure .
true.
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
Showing posts with label tricarboxylic acid cycle. Show all posts
Showing posts with label tricarboxylic acid cycle. Show all posts
Tuesday, January 8, 2008
5 - biochemistry mcqs - 31 to 40 - citric acid cycle
31 - for every NADH that passes its electrons on to the electron transport chain , approximately how many ATP are produced from the ADP and phosphate ?
answer is 3.
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32 - isocitrate lyase cleaves isocitrate to succinate and __________ in the glyoxylate pathway ?
answer is glyoxylate .
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33 - in a net reaction of the citric acid cycle , what are the reactants ?
answer is ---------- 3 NAD + plus FAD plus GDP plus PHOSPHATE plus acetyl co A .
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34 - which segment of the citric acid cycle is used in the glyoxylate pathway ?
answer is succinate to oxaloacetate .
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35 - gluconeogenesis takes place in the cytosol and the oxaloacetate must be converted for transport out of the mitochondrion .
the above statement is true .
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36 - which substrate in the citric acid cycle is coupled to the reduction of FAD to FADH2 ?
a- citrate
b- isocitrate
c- succinate
d- fumarate
answer is c .
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37 - which enzyme complex of e coli is a particle of about 4600 kD , with a diameter of 300 .
answer is pyruvate dehydrogenase .
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38 - when glucose is converted to lactate or ethanol , a relatively reduced product leaves the cell.
the above statement is true .
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39 - albert szent - gyorgyi found that cellular respiration is dramatically decreased by small amounts of succinate , fumarate , malate or oxaloacetate .
the above statement is false . the cellular respiration actually increases after adding these compounds .
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40 - the biosynthesis of which compounds uses the alpha ketoglutarate and oxaloacetate as starting materials ?
answer is amino acid biosynthesis .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
answer is 3.
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32 - isocitrate lyase cleaves isocitrate to succinate and __________ in the glyoxylate pathway ?
answer is glyoxylate .
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33 - in a net reaction of the citric acid cycle , what are the reactants ?
answer is ---------- 3 NAD + plus FAD plus GDP plus PHOSPHATE plus acetyl co A .
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34 - which segment of the citric acid cycle is used in the glyoxylate pathway ?
answer is succinate to oxaloacetate .
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35 - gluconeogenesis takes place in the cytosol and the oxaloacetate must be converted for transport out of the mitochondrion .
the above statement is true .
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36 - which substrate in the citric acid cycle is coupled to the reduction of FAD to FADH2 ?
a- citrate
b- isocitrate
c- succinate
d- fumarate
answer is c .
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37 - which enzyme complex of e coli is a particle of about 4600 kD , with a diameter of 300 .
answer is pyruvate dehydrogenase .
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38 - when glucose is converted to lactate or ethanol , a relatively reduced product leaves the cell.
the above statement is true .
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39 - albert szent - gyorgyi found that cellular respiration is dramatically decreased by small amounts of succinate , fumarate , malate or oxaloacetate .
the above statement is false . the cellular respiration actually increases after adding these compounds .
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40 - the biosynthesis of which compounds uses the alpha ketoglutarate and oxaloacetate as starting materials ?
answer is amino acid biosynthesis .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
4 - biochemistry mcqs - 21 to 30 - citric acid cycle
21 - the enzyme of the citric acid cycle that is inhibited by NADH ?
Answer is citrate synthase .
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22 - which citric acid cycle intermediates can be used for the synthesis of amino acids and can be regenerated by the same amino acids ?
a- succinyl co A and succinate
b- succinate and fumarate
c- malate and oxaloacetate
d- alpha ketogluatarate and oxaloacetate .
the correct answer is d . alpha ketoglutarate and oxaloacetate .
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23 - what is formed in a second concerted acid - base catalysed step of citrate synthase , in which the acetyl co A enol attacks oxaloacetate ?
answer is citryl co A .
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24 - which is the thiamine pyro phosphate requiring enzyme that decarboxylates pyruvate with the formation of a hydroxyethyl - TPP intermediate ?
answer is pyruvate dehydrogenase .
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25 - what is the name of the catalytically inactive E2 like protein existing in six copies that may help bind E3 to the complex .
answer is PROTEIN X .
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26 - What is the name of the cofactor that is bound to E3 and is reduced by lipoamide?
answer is FAD.
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27 - this cofactor accepts the acetyl group from the lipoamide in the pyruvate dehydrogenase complex ?
answer is coenzyme A .
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28 - This reaction is catalysed by E 3 , in which an acetyl group is transfered to co A , yielding acetyl co A and dihydrolipoamide E2 .
answer is TRANSESTERIFICATION .
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29 - Oxaloacetate undergoes transamination with alanine to produce what ?
a- glutamate and pyruvate
b- glutamate and alpha keto glutarate
c- aspartate and pyruvate
d- aspartate and alpha ketoglutarate
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30 - which enzyme produces the second CO 2 and NADH of the citric acid cycle ?
answer is alpha ketoglutarate dehydrogenase .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
Answer is citrate synthase .
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22 - which citric acid cycle intermediates can be used for the synthesis of amino acids and can be regenerated by the same amino acids ?
a- succinyl co A and succinate
b- succinate and fumarate
c- malate and oxaloacetate
d- alpha ketogluatarate and oxaloacetate .
the correct answer is d . alpha ketoglutarate and oxaloacetate .
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23 - what is formed in a second concerted acid - base catalysed step of citrate synthase , in which the acetyl co A enol attacks oxaloacetate ?
answer is citryl co A .
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24 - which is the thiamine pyro phosphate requiring enzyme that decarboxylates pyruvate with the formation of a hydroxyethyl - TPP intermediate ?
answer is pyruvate dehydrogenase .
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25 - what is the name of the catalytically inactive E2 like protein existing in six copies that may help bind E3 to the complex .
answer is PROTEIN X .
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26 - What is the name of the cofactor that is bound to E3 and is reduced by lipoamide?
answer is FAD.
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27 - this cofactor accepts the acetyl group from the lipoamide in the pyruvate dehydrogenase complex ?
answer is coenzyme A .
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28 - This reaction is catalysed by E 3 , in which an acetyl group is transfered to co A , yielding acetyl co A and dihydrolipoamide E2 .
answer is TRANSESTERIFICATION .
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29 - Oxaloacetate undergoes transamination with alanine to produce what ?
a- glutamate and pyruvate
b- glutamate and alpha keto glutarate
c- aspartate and pyruvate
d- aspartate and alpha ketoglutarate
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30 - which enzyme produces the second CO 2 and NADH of the citric acid cycle ?
answer is alpha ketoglutarate dehydrogenase .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
3 - biochemistry mcqs - 11 to 20 - citric acid cycle
11 - citrate has the ability to inhibit this enzyme by competing with oxaloacetate ?
answer is CITRATE SYNTHASE .
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12 - The molecule which inhibits isocitrate dehydrogenase ?
answer is CALCIUM . Ca +2.
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13 - this molecule regulates the citric acid cycle at many points , including the activation of pyruvate dehydrogenase phosphatase , isocitrate dehydrogenase and alpha ketoglutarate dehydrogenase .
answer is SERINE .
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14 - In e coli , this enzyme is inactivated by the phosphorylation of a serine residue in the active site ?
answer is isocitrate dehydrogenase .
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15 - covalent modification of E 1 occurs by the specific phosphorylation of WHICH residue in a reaction catalysed by pyruvate dehydrogenase kinase ?
answer is ATP .
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16 - various dicarboxylates ( alpha ketoglutarate , succinate and malate ) and a tricarboxylate ( citrate ) are rapidly oxidised by muscle tissue during respiration.
this statement is true .
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17 - which citric acid cycle intermediate can be used for the synthesis of porphyrins ?
a - succinate
b- succinyl co A
c- fumarate
d- malate
answer is b .
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18 - which possess the enzymes that mediate the net conversion of acetyl co A to oxaloacetate , which can be used for gluconeogenesis .
answer is PLANTS OR GLYOXYSOMES .
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19 - Which is the cofactor that is the substrate for E 3 and is reduced by FADH2?
Answer is NAD+
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20 - The citric acid cycle acts as a multistep catalyst that can oxidize an unlimited number of ______ groups ?
answer is acetyl groups .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
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answer is CITRATE SYNTHASE .
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12 - The molecule which inhibits isocitrate dehydrogenase ?
answer is CALCIUM . Ca +2.
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13 - this molecule regulates the citric acid cycle at many points , including the activation of pyruvate dehydrogenase phosphatase , isocitrate dehydrogenase and alpha ketoglutarate dehydrogenase .
answer is SERINE .
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14 - In e coli , this enzyme is inactivated by the phosphorylation of a serine residue in the active site ?
answer is isocitrate dehydrogenase .
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15 - covalent modification of E 1 occurs by the specific phosphorylation of WHICH residue in a reaction catalysed by pyruvate dehydrogenase kinase ?
answer is ATP .
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16 - various dicarboxylates ( alpha ketoglutarate , succinate and malate ) and a tricarboxylate ( citrate ) are rapidly oxidised by muscle tissue during respiration.
this statement is true .
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17 - which citric acid cycle intermediate can be used for the synthesis of porphyrins ?
a - succinate
b- succinyl co A
c- fumarate
d- malate
answer is b .
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18 - which possess the enzymes that mediate the net conversion of acetyl co A to oxaloacetate , which can be used for gluconeogenesis .
answer is PLANTS OR GLYOXYSOMES .
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19 - Which is the cofactor that is the substrate for E 3 and is reduced by FADH2?
Answer is NAD+
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20 - The citric acid cycle acts as a multistep catalyst that can oxidize an unlimited number of ______ groups ?
answer is acetyl groups .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
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2 - biochemistry mcqs - 1 to 10 - citric acid cycle
1 - for every FADH2 synthesised by the citric acid cycle , approximately how many number of ATP are produced from the ADP AND PHOSPHATE ?
answer is two .
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2 - which substrates in the citric acid cycle are coupled to the production of NADH ?
answers are ISOCITRATE , ALPHA KETOGLUTARATE AND MALATE .
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3 - the citric acid cycle oxidises the acetyl group of acetyl coA to how many molecules of CO2?
answer is 2 . one molecule of CO2 during the conversion of the isocitrate to alpha ketoglutarate in the presence of the enzyme isocitrate dehydrogenase , and the other during the conversion of the alpha keto glutarate to succinyl co A in the presence of the enzyme alpha keto glutarate dehydrogenase .
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4 - the enzyme which couples the cleavage of the high energy succinyl co-A to the synthesis of a high energy nucleoside triphosphate is ?
answer is SUCCINYL CO A SYNTHETASE .
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5 - the enzyme which catalyses the final reaction of the citric acid cycle regenerating the oxaloacetate is ?
answer is MALATE DEHYDROGENASE .
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6 - The enzyme which catalyses the hydration of a double bond of fumarate to form malate ?
answer is fumarase .
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7 - the enzyme which catalyses the stereospecific dehydrogenation of succinate to fumarate ?
answer is SUCCINATE DEHYDROGENASE.
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8 - in eukaryotes , all the enzymes for the citric acid cycle are located in the ?
answer is MITOCHONDRION .
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9 - lipoyllysyl arm acts as a long tether that swings the disulfide group from E1 to the E 2 active site , and finally to E 3 , where the oxidised disulfide is reduced .
the above statement is FALSE .The reduced disulfide at E3 is reoxidised .
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10 - in addition to pyruvate what are the two additional sources of acetyl co A ?
a- glucose and amino acids
b- amino acids and fatty acids
c- amino acids and glucose
d- glycogen and fatty acids
answer is B . amino acids and fatty acids .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
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answer is two .
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2 - which substrates in the citric acid cycle are coupled to the production of NADH ?
answers are ISOCITRATE , ALPHA KETOGLUTARATE AND MALATE .
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3 - the citric acid cycle oxidises the acetyl group of acetyl coA to how many molecules of CO2?
answer is 2 . one molecule of CO2 during the conversion of the isocitrate to alpha ketoglutarate in the presence of the enzyme isocitrate dehydrogenase , and the other during the conversion of the alpha keto glutarate to succinyl co A in the presence of the enzyme alpha keto glutarate dehydrogenase .
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4 - the enzyme which couples the cleavage of the high energy succinyl co-A to the synthesis of a high energy nucleoside triphosphate is ?
answer is SUCCINYL CO A SYNTHETASE .
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5 - the enzyme which catalyses the final reaction of the citric acid cycle regenerating the oxaloacetate is ?
answer is MALATE DEHYDROGENASE .
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6 - The enzyme which catalyses the hydration of a double bond of fumarate to form malate ?
answer is fumarase .
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7 - the enzyme which catalyses the stereospecific dehydrogenation of succinate to fumarate ?
answer is SUCCINATE DEHYDROGENASE.
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8 - in eukaryotes , all the enzymes for the citric acid cycle are located in the ?
answer is MITOCHONDRION .
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9 - lipoyllysyl arm acts as a long tether that swings the disulfide group from E1 to the E 2 active site , and finally to E 3 , where the oxidised disulfide is reduced .
the above statement is FALSE .The reduced disulfide at E3 is reoxidised .
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10 - in addition to pyruvate what are the two additional sources of acetyl co A ?
a- glucose and amino acids
b- amino acids and fatty acids
c- amino acids and glucose
d- glycogen and fatty acids
answer is B . amino acids and fatty acids .
TO VIEW THE CITRIC ACID CYCLE CLICK HERE
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Monday, January 7, 2008
1- citric acid cycle
click on this image for a beautiful large image .
Fig. 1: The Citric Acid Cycle
(Also Known as the Tricarboxylic Acid Cycle and the Krebs Cycle)
1. Before the pyruvates from glycolysis can feed into the citric acid cycle, they must undergo a transition reaction. The pyruvate is converted into a 2-carbon acetyl group as the third carbon is lost as CO2. The acetyl group is attached to coenzyme A to form acetyl-CoA.
2. The 2-carbon acetyl-CoA combines with the 4-carbon oxaloacetate of the citric acid cycle to form 6-carbon citrate.
3. Citrate is converted to isocitrate.
4. The 6-carbon isocitrate is oxidized by NAD+ to produce reduced NADH and 5-carbon alpha-ketoglutarate. (One carbon is lost as CO2.)
5. The 5-carbon alpha-ketoglutarate is oxidized by NAD+ to produce reduced NADH and 4-carbon succinyl-CoA. (One carbon is lost as CO2.)
6. Oxidation of succinyl-CoA produces succinate and one GTP that is converted to ATP.
7. Oxidation of succinate by FAD produces reduced FADH2 and fumarate.
8. Fumarate is converted into malate.
9. Oxidation of malate by NAD+ produces reduced NADH and oxaloacetate.
The two molecules of acetyl-CoA from the transition reaction enter the citric acid cycle. This results in the formation of 6 molecules of NADH, two molecules of FADH2, two molecules of ATP, and four molecules of CO2. The NADH and FADH2 molecules then carry electrons to the electron transport system for further production of ATPs by oxidative phosphorylation.
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