View
- Term
- Definition
- Both Sides
Study
- All (49)
Shortcut Show
Next
Prev
Flip
BBMB 405: REVIEW QUESTIONS
20. Why is the Calvin cycle crucial to the functioning of all life forms?
|
The Calvin cycle is the primary means of converting gaseous CO2 into organic matter -- that is, biomolecules. Essentially, every carbon atom in your body passed through rubisco and the Calvin cycle at some time in the past
|
20. Identify the similarities and differences between the Krebs cycle and the Calvin cycle.
|
Calvin Cycle: stroma, carbon chemistry for photosynthesis, fixes CO2, requires NADPH, Regenerates starting compound (ribulose 1,5-bisphosphate), requires ATP, complex stoichiometry
Krebs Cycle: matrix, for oxidative phosphorylation, releases CO2, generates NADPH, regenerates starting compound (oxaloacetate),generates ATP or GTP, simple stoichiometry
|
20. The Calvin cycle can be thought of as occurring in three parts or stages. Describe stages.
|
Stage 1: CO2 fixation with ribulose 1,5-bisphosphate and the subsequent formation of 3-phosphoglycerate. Stage 2 is the conversion of some of the 3-phosphoglycerate into hexose. Stage 3 is the regeneration of ribulose 1,5-bisphosphate.
|
20. An illuminated suspension of Chlorella is actively carrying out photosynthesis. Suppose that the light is suddenly switched off. How would the levels of 3-phosphoglycerate and ribulose 1,5-bisphosphate change in the next minute?
|
The concentration of 3-phosphoglycerate would increase, whereas that of ribulose 1,5-bisphosphate would decrease
|
20. Why is the C4 pathway valuable for tropical plants?
|
The C4 pathway allows the CO2 concentration to increase at the site of carbon fixation. High concentrations of CO2 inhibit the oxygenase reaction of rubisco. This inhibition is important for tropical plants because of the oxygenase activity increases more rapidly with temperature than does the carboxylase activity
|
20. What is photorespiration, what is its cause, and why is it believed to be wasteful?
|
Photorespiration is the consumption of oxygen by plants with the production of CO2, but it does not generate energy. Photorespiration is due to the oxygenase activity of rubisco. It is wasteful because, instead of fixing CO2 for conversion into hexoses, rubisco is generating CO2
|
20. Describe how the pentose phosphate pathway and glycolysis are linked by transaldolase and transketolase.
|
The enzymes catalyze the transformation of the five carbon sugar formed by the oxidative phase of the PPP into fructose 6-phosphate and GAP, intermediates in glycolysis (and glucogenesis)
|
20. Glucose labeled with 14C at C-6 is added to a solution containing the enzymes and cofactors of the oxidative phase of the PPP. What is the fate of the radioactive label?
|
The label emerges at C-5 of ribulose 5-phosphate
|
19. PSI produces a powerful reductant, whereas PSII produces a powerful oxidant. Identify the reductant and oxidant and describe their roles.
|
PSI generates ferredoxin, which reduces NADP+ to NADPH, a biosynthetic reducing power. PSII activates the Mn complex, an oxidant capable of oxidizing water, generating electrons for photosynthesis and generating protons to forma proton gradient and to reduce NADP+ and O2
|
19. What is advantage of having an extensive set of thylakoid membranes in the chloroplasts?
|
The light reactions take place on thylakoid membranes. Increasing the membrane surface increases the number of ATP and NADH generating sites
|
19. What is the ultimate electron acceptor in photosynthesis? The ultimate electron donor? What powers the electron flow between the donor and the acceptor?
|
NADP+ is the acceptor. H2O is the donor. Light energy.
|
What fracton of the energy is 700 nm light absorbed by PSI trapped as high energy electrons?
|
56%
|
19. Dichlorophenyldimethylurea(DCMU), a herbicide, interferes with photophosphorylation and O2 evolution. However, it does not block O2 evolution in the presence of an artificial electron acceptor. Propose a site for the inhibitory action of DCMU.
|
DCMU inhibits electron transfer in the link between PSII and PSI. O2 can evolve in the presence of DCMU if an artificial electron acceptor such as ferricyanide can accept electrons from Q.
|
19. Predict the effect of DCMU on a plant's ability to perform cyclic photophosphorylation.
|
DCMU will have no effect, because it blocks PSII, and cyclic photophosphorylation uses PSI and the cyctochrome bf complex.
|
19. What structural feature of mitochondria corresponds to the thykaloid membrane?
|
cristae |
19. (1 of 2) Compare and contrast oxidative phosphorylation and photosynthesis.
|
In eu, both processes take place in specialized organelles. Both depend on high energy electrons to generate ATP. In oxidative phosphorylation the high energy electrons originate in fuels are extracted as reducing power in the form of NADH. In photosynthesis the high energy electrons are generated by light and are captured as reducing power in the form of NADPH.
|
19. (2 of 2) Compare and contrast oxidative phosphorylation and photosynthesis.
|
Both processes use redox rxn to generate a proton gradient, and the enzymes that convert the proton gradient into ATP are very similar in both processes. In both, electron transport takes place in membranes inside organelles.
|
20. When Melvin Calvin performed his initial experiments on carbon fixation, he exposed algae to radioactive carbon dioxide. After 5 seconds, only a single organic compound contained radioactivity but after 60 sec, many compounds had incorporated radioactivity. (a) What compound initially contained the radioactivity? (b) What compounds contained radioactivity after 60 seconds?
|
(a) 3-phosphoglycerate (b) The other members of the Calvin cycle
|
20. Suggest a reason why rubisco might be the most abundant enzyme in the world.
|
It catalyzes a crucial reaction, but it is highly inefficient. Consequently, it is required in large amounts to overcome its slow catalysis.
|
20. GAP dehydrogenase in chloroplasts uses NADPH to participate in the synthesis of glucose. In gluconeogensis in the cytoplasm, the isozyme of the dehydrogenase uses NADH. Why is it advantageous for the chloroplast enzyme to use NADPH?
|
Because NADPH is generated in the chloroplasts by the light reactions
|
20. Write a balance equation for the tranamination of glyocylate to yield glycine.
|
Asparate + glyoxylate --> oxaloacetate + glycine
|
20. Before pampered lawns, most lush lawns of May would often convert into cultures of crabgrass in the dog days of August. Provide an explanation for this.
|
The oxygenase activity of rubisco increases with temperature. Crabgrass is a C4 plant, whereas most grasses lack the capability. Consequently, the crabgrass will thrive at the hottest part of the summer beacuse the C4 pathway provides an ample supply of CO2.
|
20. Why is the C4 pathway valuable to tropical plants?
|
The C4 pathway allows the CO2 concentration to increase at the site of carbon fixation. High concentrations of CO2 inhibit the oxygenase reaction of rubisco. This inhibition is important for tropical plants because the oxygenase activity increases more rapidly with temperature than does the carboxylase activity.
|
20. Explain why maintaining a high concentration of CO2 in the bundle sheath cells of C4 plants is an example of active transport. How much ATP is required per CO2 to maintain a high concentration of CO2 in the bundle sheath cells of C4 plants?
|
ATP is required to form PEP from pyruvate. The PEP combines with CO2 to form oxaloacetate and subsequently malate. Two ATP molecules are required because a second ATP molecule is requried to phosphorylate AMP to ADP
|
20. What is photorespiration, what is its cause, and why is it believed to be wasteful?
|
Photorespiration is the consumption of oxygen by plants with the production of CO2, but it does not generate energy. Photorespiration is due to oxygenase activity of rubisco. It is wasteful because instead of fixing CO2 for conversion into hexoses, rubisco is generating CO2
|
20. What are the light dependent changes in the stroma that regulate the Calvin cycle?
|
The light reactions lead to an increase in the stromal concentrations of NADPH, reduced ferredoxin, and Mg++, as well as an increase in pH
|
20. Describe how the PPP and glycolysis are linked by transaldolase and transketolase.
|
The enzymes catalyze the transformation of the five carbon sugar formed by the oxidative phase of the PPP into fructose 6- phosphate and GAP intermediates in glycolysis and glucogenesis
|
20. Glucose labeled with 14C at C-6 is added to a solution containing the enzymes and cofactors of the oxidative phase of the PPP. What is the fate of the radioactive label?
|
the label emerges at C-5 of ribulose 5-phosphate
|
20. What is the stoichiometry of the synthesis of (a) ribose 5-phosphate from glucose 6-phosphate without the concomitant generation of NADPH? (b) NADPH from glucose 6-phosphate without the concomitant formation of pentose sugars?
|
(a) 5 glucose 6-phosphate + ATP --> 6 ribose 5-phosphate + ADP + H+ (b) glucose 6-phosphate + 12 NADP+ + 7 H2O --> 6 CO2 + 12 NADPH + 12 H+ + Pi
|
20. Liver and other organ meats contain large quantities of nucleic acids. In the course of digestion, RNA is hydrolyzed to ribose, among other chemicals. Explain how ribose can be used as a fuel.
|
The nonoxidative phase of the PPP can be used to convert three molecules of ribose 5-phosphate into two molecules of fructose 6-phosphate and one molecules of GAP. These molecules are components of the glycotic pathway
|
20. Glucose is normally completely oxidized to CO2 in the mitochondria. In what circumstance can glucose be complete oxidized to CO2 in the cytoplasm?
|
When much NADPH is required. THe oxidative pathway is followed by the nonoxidative phase. The resulting fructose 6-phosphate and GAP are used to generate glucose 6-phosphate through gluconeogenesis, adn the cycle is repeated until the equivalent of one glucose molecules is oxidized to CO2
|
20. Why do deficiencies in glucose 6-phosphate dehydrogenase frequently present as anemia?
|
Because RBC do not have mitochondria and the only means to obtain NADPH is through the PPP. There are biochemical means to convert mitochondrial NADH into cytoplasmic NADPH.
|
20. What is the role of glutathione in protection against damage by reactive oxygen species? Why is the PPP crucial to this protection?
|
Reactive peroxides are a type of reactive oxygen species. The enzyme glutathione peroxidase uses reduced glutathione to neutralize peroxides by converting them into alcohols while generating oxidized glutathione. Reduced glutathione is regenerated by glutathione reductase witht he used of NADPH, the product of the oxidative phase fo the PPP
|
21. Glycogen is not as reduced as fatty acids are and consquently not as energy rich. Why do animals store any energy as glycogen? Why not convert all excess fuel into fatty acids?
|
The controlled breakdown of glycogen and release of glucose increase the amount of glucose that is available between meals. Hence, glycogen serves as a buffer to maintain blood glucose levels. Glycogen's role in maintaining blood glucose levels is especially important because glucose is virtually the only fuel used by the brain, except during prolonged starvation. Can privide energy in the absence of th O2. Goood for studden activity
|
21. alpha-Amylose is an unbranched glucose polymer. Why would this polymer not be as effective a storage form of glucose as glycogen?
|
As an unbranched polymer, alpha amylose has only one nonreducing end. Therefore, only one glycogen phosphorylase molecule could dgrade each alpha amylose molecule. Because glycogen is highly branched, there are many nonreducing ends per molecule. Consequently, many phosphorylase molecules can release many glucose molecules per glycogen molecule
|
21. A sample of glycogen from a patient with liver disease is incubated with orthophosphate, phosphorylase, the transferase and the debranching enzyme. The ratio of glucose 1 phosphate to glucose formed in this mixture is 100. What is the most likely enzymatic deficiency in this patient?
|
the patient has a deficiency of the branching of the branching enzyme
|
21. Compare the allosteric regulation of phosphorylase in the liver and in muscle, and explain the significance of the difference.
|
In muscle, the b form of phosphorylase is activated by AMP. In the liver, the a form is inhibited by glucose. The difference corresponds to the difference int he metabolic role of glycogen in each tissue. Muscle uses glycogenas a fuel for contraction, where as the liver uses it to maintain blood glucose levels
|
21. Suggest an explanation for the fact that the amount of glycogen in type I glycogen storage disease (von Gierke disease) is increased.
|
The high lecel of G-6-P in this disease resulting form the absence of G-6 phosphotase or the transporter, shifts the allosteric equilibruim of phosphorylated glycogen synthasetoward the active form
|
Hers disease results form an absence fo liver glycogen phosphorylase and may result in serious illness, In McArdle disease muscle glycogen phosphorylase is absent. ALthough exercise is difficult for patients suffering from thism the disease is rarely life threatening. Account for the different manifestations of the absence of glycogen phosphoylase in two tissues. What does the existence of these two different diseases indicate about the genetic nature of the phosphorylase?
|
THe different manifestations correspond to the different roles of the liver and muscle. Liver glycogen phosphorylase plays a crucial role in the maintenance fo blood glucose levels. Muscle glu phosphorylase provvides flucose wonly for the muscle. This suggests there are two different isozymic forms of the glycogen phorphorylase
|
21. Outline the signal transduction cascade for glycogen degradation in muscle.
|
Epinephrine binds to its G protein coupled receptor. THe resulting structural changes activate a Ga protein which in turn activated adenyl cyclase. Adenyl cyclase synthesizes cAMP, which activates protein kinase A. PKA partly activates phosphoryl kinase, whcih phosphorylates and activates flycogen phoshporylase. THe Ca++ released during muscle contraction further activates the phosphorylase kinase, leading to further stimulation of glycogen phosphorylase
|
21. THere must be a way to shut down glycogen breakdown quickly to prevent the wasteful depletion of glycogen after energy needs have been met. What mechanisms are employed to turn off glycogen breakdown?
|
FIrst, the signal transduction pathway is shut down when the initiating hormone is no longer present. Second, the inherent GTPase activity of the G protein converts the bound GTP into inactive GDP. Thirs phoshpodiesterases convert cyclic AMP into AMP. Fourth, PP1 removes the phoshoryl group from glycogen phosphorylase, converting the enzyme into usually inactive b form
|
21. Phosphorylation has opposite effects on glycogen synthesis and breakdown. WHat is the advantage of its having opposing effects?
|
It prevents both from operating simultaneously which would lead to a useless expenditure of energy
|
21. THe complete oxidation of G-6-P derived from free glucose yields 30 molecules ATP, where as the complete oxidation of g-6-P derivedfrom glycogenyields 31 molecules of ATP. Account for difference.
|
Free glucose must be phosphorylated at the expense of a molecule of ATP. G-6-P derived form glycogen is formed yb phosphorolytic cleavage, thus sparing one molecule of ATP. Thus, the net yield of ATP when glycogen derived glucose processd to pyruvate is three moelcules of ATP compared with two molecules of ATP form free glucose
|
21. How does insulin stimulate glycogen synthesis?
|
Insulin binds to its receptor and activates the tyrosine kinase activity receptor which in turn triggers a pathway that activates protein kinases. PP1 then removes the phosphate from glycogen synthase and thereby activates the synthase
|
22. Place the following list of reactions or relevant locations in the beta oxidation of fatty acids in the proper order.
|
fatty acids in cytoplasm, activation of fatty acid by joining to CoA, reaction with carnitine, acyl CoA in mitochondrian, FAD-linked oxidation, hydration, NAD+ linked oxidation, thiolysis
|
22. In the equation for fatty acid degradation shown here, only seven molecules of CoA are required to yield eight molecules of acetyl CoA. How is this difference possible?
|
The next to last degradation product, acetoacetyl CoA, yields 2 molecules of acetyl CoA with thiolysis by only one molecule if CoA`
|
22. Compare the ATP yields from palmitic acid and palmitoleic acid.
|
Plamitic acid yields 106 molecules of ATP. Palmitoleic acid has a double bond between carbons C9 and C10. WHen palmitoleic acid is processed in Beta oxidation, one of the oxidation steps will not take place, because a double bond already exists. Thus, FADH2 wil not be generated and palmitoleic acid will yield 1.5 fewer molecules of ATP than plamitic acid, for a total of 104.5 molecules of ATP
|
22. How much energy is attained with the complete oxidation of the ketone body D-3-hydroxybutyrate?
|
NADH produced with the oxidation to acetoacetate = 2.5 ATP. Acetoacetate is converted into acetoaceyl CoA. Two molecules of acetyl CoA result from the hydrolysis of acetoacetyl CoA, each worth 10 ATP when processed by the citric acid cycle. TOtal ATP yield is 22.5
|
22. Just check the review questions
|
... |