Ch. 20

In what ways does photosynthesis in C4 plants differ from photosynthesis in C3 plants?

C4 plants use one set of cells to fix carbon and another set of cells to produce sugars. C4 plants can continue to make sugars on hot, dry days when the stomata are closed C4 plants do not produce sugars as efficiently as C3 plants during cool, wet conditions

How does F26BP regulate these two enzymes, and therefore sucrose synthesis?

FBPase-1 is inhibited, PP-PFK is stimulated, sucrose synthesis slows

The last step of glycolysis converts phosphoenolpyruvate to pyruvate: phosphoenolpyruvate + ADP --> pyruvate + ATP ΔG = -33 kJ/mol (-7.5 kcal/mol) via pyruvate kinase The ΔG°\' of the reverse reaction is 31 kJ/mol ( 7.5 kcal/mol). Instead of reversing the pyruvate kinase reaction, the step is bypassed in gluconeogenesis. Several steps for the conversion of pyruvate to phosphoenolpyruvate via gluconeogenesis are given below. Place the steps in the correct order. You will not place all the steps.

In the mitochondrion, pyruvate carboxylase converts pyruvate to oxaloacetate. Malate dehydrogenase in the mitochondrion reduces oxaloacetate to malate. Malate dehydrogenase in the cytoplasm oxidizes malate to oxaloacetate. Phosphoenolpyruvate carboxykinase decarboxylates and phosphorylates oxaloacetate, forming phosphoenolpyruvate.

Which of the following is associated with light and dark?

Light: -increased triose phosphate concentration -photosynthesis Dark: -increased Pi concentration

Depending on conditions, plants convert the triose phosphates from the Calvin cycle into starch or sucrose. Which of the following statements is true?

Starch is made in the chloroplast while sucrose is made in the cytoplasm.

How would the following influence the activity of this enzyme?

Stimulate activity and starch synthesis: -high [3PG] in chloroplast -decreased triose phosphate transport into cytosol -light Inhibit activity and starch synthesis -high [Pi]

The enzyme ribulose bisphosphate carboxylase/oxygenase, or rubisco, fixes carbon dioxide. The carbon dioxide is incorporated into a five-carbon compound, which is then hydrolyzed to yield two three-carbon compounds. Place the steps of the rubisco carboxylation reaction in order, beginning with the substrate.

Substrate Rubisco removes a proton from C3 of ribulose-1,5-bisphosphate An enediolate intermediate nucleophilically attacks CO2, incorporating it at C2 Water attacks C3 of the six-carbon beta-keto acid, hydrating it The six-carbon molecule splits, yielding two 3-phosphoglycerate molecules Product

Which of the following scenarios is a direct effect of the absence of carbon dioxide during photosynthesis?

The carbon fixation stage of the Calvin cycle would be unable to synthesize the sugar 3-PGA.

What is the function of the enzyme rubisco?

catalyzes the fixation of carbon dioxide to ribulose bisphosphate during the Calvin cycle.

The reaction written below describes the activation of glucose to form the substrate for starch synthesis in plants. Identify the enzyme that catalyzes the reaction.

glucose-1 phosphate + ATP --> ADP-glucose + PPi via ADP-glucose pyrophosphorylase

Plants use intermediates from the Calvin cycle to synthesize carbohydrates like starch, cellulose, and sucrose. Label the flowchart of sucrose synthesis by moving the molecule names to the appropriate places. One of the labels will be used twice.

glyceraldehyde-3-phosphate + dihydroxyacetone phosphate --> fructose 1,6-bisphosphate --> fructose-6-phosphate --> glucose-6-phosphate --> glucose-1-phosphate --> UDP-glucose --> sucrose-6-phosphate --> sucrose

Label the diagram of the Calvin cycle. Not all labels will be used. Scroll down to see all the labels.

glyceraldehyde-3-phosphate-->ribulose 5-phosphate-->(ATP-->ADP)ribulose 1,5-bisphosphate-->(CO2 enters) 3-phosphoglycerate -->(ATP-->ADP) 1,3 bisphosphoglycerate-->(NADPH-->NADP + Pi) glyceraldehyde-3-phosphate

Which of the following stimulates PFK-2, and therefore increases F26BP concentration?

increased Pi concentration

Is sucrose synthesis favored in the light or dark?

light

The body synthesizes glucose from non-carbohydrate sources via gluconeogenesis. Pyruvate, oxaloacetate, and dihydroxyacetone phosphate are entry points for the gluconeogensis pathway. Although gluconeogenesis seems like the reverse of glycolysis, gluconeogenesis uses some different enzymes to bypass the irreversible reactions of glycolysis. Complete the diagram of gluconeogenesis by moving the three compounds and four enzymes to their correct locations in the pathway.

pyruvate --> oxaloacetate (pyruvate carboxylase; ATP + HCO2 --> ADP + Pi) oxaloacetate --> PEP (PEP carboxykinase; GTP + GDP + CO2) fructose-1,6-bisphosphate --> fructose-6-phosphate (fructose bisphosphatase; Pi released) glucose-6-phosphate --> glucose (glucose-6-phosphatase; Pi released)

Consider the fructose-1,6-bisphosphatase reaction. Calculate the free energy change if the ratio of the concentrations of the products to the concentrations of the reactants is 24.5, and the temperature is 37.0 °C? ΔG°\' for the reaction is -16.7 kJ/mol. The constant R = 8.3145 J/(mol·K)

ΔG=-8.46 kJ/mol