Name:
2 points
Chem 465
Biochemistry II
Multiple choice (4 points apiece):
1. When a muscle is stimulated to contract aerobically, less lactic acid is formed than when it
contracts anaerobically because:
A) glycolysis does not occur to significant extent under aerobic conditions.
B) muscle is metabolically less active under aerobic than anaerobic conditions.
C) the lactic acid generated is rapidly incorporated into lipids under aerobic conditions.
D) under aerobic conditions in muscle, the major energy-yielding pathway is the pentose
phosphate pathway, which does not produce lactate.
E) under aerobic conditions most of the pyruvate generated as a result of glycolysis is
oxidized by the citric acid cycle rather than reduced to lactate.
2. If glucose labeled with 14C at C-1 (the aldehyde carbon) were metabolized in the liver, the first
radioactive pyruvate formed would be labeled in:
A) all three carbons.
B) both A and C.
C) its carbonyl carbon.
D) its carboxyl carbon.
E) its methyl carbon.
3. Which of the following is a cofactor in the reaction catalyzed by glyceraldehyde 3-phosphate
dehydrogenase?
A) ATP
B) Cu 2+
C) heme
D) NAD+
E) NADP+
4. Which of the following statements about the oxidative decarboxylation of pyruvate in aerobic
conditions in animal cells is correct?
A) One of the products of the reactions of the pyruvate dehydrogenase complex is a
thioester of acetate.
B) The methyl (-CH3) group is eliminated as CO2.
C) The process occurs in the cytosolic compartment of the cell.
D) The pyruvate dehydrogenase complex uses all of the following as cofactors: NAD+,
lipoic acid, pyridoxal phosphate (PLP), and FAD.
E) The reaction is so important to energy production that pyruvate dehydrogenase
operates at full speed under all conditions.
5. Which of the following is not an intermediate of the citric acid cycle?
A) Acetyl-coA
B) Citrate
C) Oxaloacetate
D) Succinyl-coA
E) á-Ketoglutarate
6. All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD+ except
the reaction catalyzed by:
A) isocitrate dehydrogenase.
B) malate dehydrogenase.
C) pyruvate dehydrogenase
D) succinate dehydrogenase.
E) the á-ketoglutarate dehydrogenase complex.
7. Citrate synthase and the NAD+-specific isocitrate dehydrogenase are two key regulatory
enzymes of the citric acid cycle. These enzymes are inhibited by:
A) acetyl-CoA and fructose 6-phosphate.
B) AMP and/or NAD+.
C) AMP and/or NADH.
D) ATP and/or NAD+.
E) ATP and/or NADH.
8. What is Pentose phosphate pathway?A metabolic pathway where G-6P is oxidized to a 5C
sugar. This process generates ribose for RNA and DNA, and NADPH for synthetic pathways.
Next, six 5C sugars are shuffled around to make five -6C sugars. Two reasons for this pathway
area: (1) to make ribose for RNA and DNA and (2) to make NADPH for synthetic pathways.
9. This page is blank because I want you to fill it in with the glycolytic pathway from glucose to
pyruvate by showing the structure of all intermediates. At each step also give the name of the
enzyme and ÄG of the reaction. To help you on your way, here is a list of all then enzymes in
alphabetical order: Aldolase, Enolase, Glyeraldehyde 3-phosphate dehydrogenase, Hexokinase,
Phosphofructokinase-1, Phosphoglycerate kinase, Phosphoglycerate mutase, Phosphohexose
isomerase, Pyruvate kinase, Triose phosphate isomerase.
On this key I am not going to take the time to make the structures, but I will check that you have
the correct structure
Glucose + ATP
Hexokinase
Mg2+
-16.7
Glucose-6-P
Phosphohexose isomerase
Mg2+ +1.7
Fructose-6-P + ATP
Phosphofructosekinase -1
Mg2+ -14.2
Fructose 1,6-bisphosphate
aldolase
+23.8
Dihydroxyacetone phosphate
Glyceraldehyde 3-phosphate
Triose isomerase
+7.5
Glyceraldehyde 3phosphate + NAD
glyceraldehyde 3-phosphate dehydrogenase
+ 6.3
1,3-Bisphosphoglyerate
phosphoglycerate kinase
Mg2+ -18.5
3-Phosphoglycerate + ATP
Phosphoglyerate mutase
Mg2+ +4.4
2-Phosphoglycerate
Enolase
Mg2+ +7.5
Phophoenolpyruvate
Pyruvate kinase
K+, Mg2+ or Mn2+
-31.4
Pyruvate + ATP
10. Sketch the pathway in which pyruvate is completely oxidized to CO2. In this pathway be sure
to identify all reactions that generate ATP, GTP, NADH or FADH2. Also show the anapleotropic
reaction that are used to fill in TCA intermediates when they are depleted.
I would prefer structures for all intermediates, and a cycle, but this is something I can put in with
a word processor
Pyruvate
pyruvate dehydrogenase
CoASH,NAD, TPP,Lippoate, FAD -33.3
Acetyl CoA
(Oxaloacetate)
citrate syntase
-32.2
Citrate
aconitase
Iron-sulfur center
13.3
Isocitrate + NAD 6NADH
isocitrate dehydrogenase
Mn2+ NAD
-20.9
á-ketoglutarate + NAD 6NADH
á-ketoglutarate dehydrogenase CoASH,NAD, TPP,Lippoate, FAD -33.5
Succinyl CoA + GDP or ADP 6GTP or ATP
Succinyl-CoA synthetase
-2.9
Succinate + FAD 6FADH2
Succinate dehydrogenase
FAD, FeS clusters
0
Fumarate
fumarase
-3.8
L-malate + NAD 6NADH
l-malate dehydrogenase
29.7
Oxaloacetate
Anapleotropic:
Pyruvate + HCO3- + ATP 6Oxaloacetate + ADP + Pi
PEP + CO2 + GDP 6 oxaloacetate + GTP
PEP + HCO3- 6oxaloacetate + Pi
Pyruvate + HCO3- + NADH6 malate + NAD
pyruvate carboxylase
PEP carboxykinase
PEP carboxylase
malic enzyme
11.Dynamic Steady State
State of a living cell where concentrations of intermediates are constant, not because they
are at equilibrium, but because the rate of creation = rate of destruction.
Homeostasis
A properly balanced metabolism is keeping all input = to all output, so on a whole
nothing changes in the entire organism.
Futile cycle
In glycolysis there are two steps where ATP is used to phosphorylate a sugar and one step
where PEP is dephosphorylated to generate ATP. These three reaction have such large free
energy that they cannot be reversed, so in gluconeogenesis, a different reaction is used. In the
case of the phosphorylated sugars the phosphate is simple removed and in the case of PEP, 2
ATP’s are used to take pyruvate back to PEP. If any of the glycolytic reaction are directly
coupled to the corresponding gluconeogenic reaction, the intermediates would simply cycle back
and forth,, degrading ATP to ADP and Pi. This cycling of a reactant to a product and back to a
reactant, concurrently hydrolysing ATP to ADP and Pi using two different enzymes, is what is
called a futile cycle.
Substrate level phosphorylation
Where ATP is generated by directly transferring a phosphate from one high energy
substrate containing a phosphate to an ADP molecule.
Respiration linked phosphorylation
When High energy intermediate like NADH or FADH2 is used to transfer protons across
a membrane to create an electrochemical gradient, and then a second system allows protons to
return to the organelle, coming ‘down’ the electrochemical gradient, and this is linked to making
ATP from ADP and Pi
Thioester
C=O
|
S-R
Lactic acid fermentations
Pyruvate + NADH 6NAD+ + lactic acid
Ethanolic fermentation
Pyruvate 6Acetaldehyde + CO2 , Acetaldhyde + NADH 6Ethanol + NAD+
Ambibolic pathway
a pathway that functions in both catabolism and anabolism
Anapleotropic reation
One that is used to fill in intermediates that have been siphoned off by other processes.
Glyoxylate cycle
A pathway found in plants that allows the net synthesis of glucose from fatty acids
12.
Controls of Pyruvate to CO2
A diagram like Figure 16-18
Pyruvate dehydrogenase
Inhibited by ATP, Acetyl CoA, NADH Fatty acid
Accelerated by AMP, CoA, NAD+, Ca 2+
Citrate Synthase
Inhibited by NADH, succinylCoA, citrate, ATP
Accelerated by ADP
Isocitrate dehydrogenase
Inhibited by ATP
Accelerated by Ca 2+, ADP
á-ketoglutarate dehydrogenase
inhibited: succinyl CoA, NADH
accelerated: Ca 2+
13. Diagram like 14-19 from text
Left hand pathway
Pyruvate to Oxaloacetate by pyuvate carboxylase - an anapleotropic reaction in Kreb
Oxaloacetate to Malate reverse of reaction used in Krebs, (but O to M direction is
actually the favorable direction for this reaction under standard state conditions!)
Right hand pathway
Pyruvate to Oxaloacetate by pyruvate carboxylase - an anapleotropic reaction in Kreb
Oxaloacetate to PEP - PEP carboxykinase - A reaction normally used to draw off
oxaloacetate to make PEP to be used in the synthesis of other compounds like glucose and Ser,
Gly, Cys, Phe, Tyr, and Trp