Cellular Respiration and Photosynthesis
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GRE Subject Test: Biochemistry, Cell, and Molecular Biology › Cellular Respiration and Photosynthesis
At which complex in the electron transport chain is NADH oxidized?
Complex I
Complex II
Complex III
Complex IV
Explanation
NADH is the first electron carrier to be oxidized by the electron transport chain, a process that occurs at complex I. FADH2 is oxidized further down the chain in complex II, causing it to produce less ATP on average than NADH.
At which complex in the electron transport chain is NADH oxidized?
Complex I
Complex II
Complex III
Complex IV
Explanation
NADH is the first electron carrier to be oxidized by the electron transport chain, a process that occurs at complex I. FADH2 is oxidized further down the chain in complex II, causing it to produce less ATP on average than NADH.
Lactate dehydrogenase inhibitor is added to a mixture of cells. Which of the following molecules will build up inside a cell undergoing aerobic respiration?
None of these molecules will build up
Pyruvate
NADH
Both of these molecules will build up
Explanation
The question states that the cell undergoes aerobic respiration. This means that the products from anaerobic respiration (glycolysis) will go through Krebs cycle and electron transport chain (aerobic respiration) to generate ATP. Lactate dehydrogenase is an enzyme important for converting the pyruvate molecules (from glycolysis) to lactate and oxidizing NADH. This reaction occurs in anaerobic fermentation when there is tissue hypoxia (decrease in oxygen).
If this inhibitor was placed in a cell that is deprived of oxygen, then there would be a buildup of pyruvate and NADH; however, since the inhibitor is added to cells undergoing aerobic respiration there will be no buildup. The pyruvate and NADH will undergo aerobic respiration and generate ATP. Note that red blood cells (RBCs) are unique in that they only use anaerobic respiration for ATP; therefore, adding lactate dehydrogenase inhibitor to RBCs will lead to a buildup of pyruvate and NADH.
Lactate dehydrogenase inhibitor is added to a mixture of cells. Which of the following molecules will build up inside a cell undergoing aerobic respiration?
None of these molecules will build up
Pyruvate
NADH
Both of these molecules will build up
Explanation
The question states that the cell undergoes aerobic respiration. This means that the products from anaerobic respiration (glycolysis) will go through Krebs cycle and electron transport chain (aerobic respiration) to generate ATP. Lactate dehydrogenase is an enzyme important for converting the pyruvate molecules (from glycolysis) to lactate and oxidizing NADH. This reaction occurs in anaerobic fermentation when there is tissue hypoxia (decrease in oxygen).
If this inhibitor was placed in a cell that is deprived of oxygen, then there would be a buildup of pyruvate and NADH; however, since the inhibitor is added to cells undergoing aerobic respiration there will be no buildup. The pyruvate and NADH will undergo aerobic respiration and generate ATP. Note that red blood cells (RBCs) are unique in that they only use anaerobic respiration for ATP; therefore, adding lactate dehydrogenase inhibitor to RBCs will lead to a buildup of pyruvate and NADH.
The first step of glycolysis hydrolyzes ATP to ADP and inorganic phosphate. What happens to the glucose molecule during this step?
The glucose is phosphorylated
The glucose is dephosphorylated
The glucose is converted to fructose
Glucose is cleaved into two molecules of pyruvate
The glucose is cleaved into two molecules of glyceraldehyde-3-phosphate
Explanation
The first step of glycolysis consumes a molecule of ATP, removing one of the phosphate groups to make ADP. This phosphate group is added to glucose to make Glucose-6-phosphate, therefore glucose is phosphorylated.
The first step of glycolysis hydrolyzes ATP to ADP and inorganic phosphate. What happens to the glucose molecule during this step?
The glucose is phosphorylated
The glucose is dephosphorylated
The glucose is converted to fructose
Glucose is cleaved into two molecules of pyruvate
The glucose is cleaved into two molecules of glyceraldehyde-3-phosphate
Explanation
The first step of glycolysis consumes a molecule of ATP, removing one of the phosphate groups to make ADP. This phosphate group is added to glucose to make Glucose-6-phosphate, therefore glucose is phosphorylated.
Which of the following is true regarding electron transport chain (ETC)?
I. Proton pump generates ATP
II. Electron affinity of and
is lower than the carriers in ETC
III. Electrochemical gradient of sodium facilitates production of ATP
II only
I only
I and II
II and III
Explanation
Electron transport chain is a series of electron carriers located on the inner membrane of the mitochondria. Electrons traverse across these electron carriers and this motion allows for the proton pump to generate a proton gradient across the inner membrane. This gradient is generated by pumping protons from the inside of the mitochondria to the periplasmic space (space between inner and outer mitochondrial membranes). The excess protons in the periplasmic space are transported back into the mitochondria and this movement facilitates the generation of ATP by the ATP synthase. Note that ATP is generated by ATP synthase, not the proton pump.
and
are electron carriers that carry electrons from glycolysis and Krebs cycle. These carriers enter the ETC and donate their electrons to the carriers in ETC. This occurs because ETC carriers have higher affinity for electrons. Remember that each subsequent carrier in ETC has a higher affinity for electrons, so that it is able to snatch the electron from the previous carrier. As mentioned, the ATP generation is facilitated by the proton gradient, not the sodium gradient.
Which of the following is true regarding electron transport chain (ETC)?
I. Proton pump generates ATP
II. Electron affinity of and
is lower than the carriers in ETC
III. Electrochemical gradient of sodium facilitates production of ATP
II only
I only
I and II
II and III
Explanation
Electron transport chain is a series of electron carriers located on the inner membrane of the mitochondria. Electrons traverse across these electron carriers and this motion allows for the proton pump to generate a proton gradient across the inner membrane. This gradient is generated by pumping protons from the inside of the mitochondria to the periplasmic space (space between inner and outer mitochondrial membranes). The excess protons in the periplasmic space are transported back into the mitochondria and this movement facilitates the generation of ATP by the ATP synthase. Note that ATP is generated by ATP synthase, not the proton pump.
and
are electron carriers that carry electrons from glycolysis and Krebs cycle. These carriers enter the ETC and donate their electrons to the carriers in ETC. This occurs because ETC carriers have higher affinity for electrons. Remember that each subsequent carrier in ETC has a higher affinity for electrons, so that it is able to snatch the electron from the previous carrier. As mentioned, the ATP generation is facilitated by the proton gradient, not the sodium gradient.
Anaerobic metabolism occurs in the __________; fermentation occurs in the __________.
cytoplasm . . . cytoplasm
cytoplasm . . . mitochondria
mitochondria . . . cytoplasm
mitochondria . . . mitochondria
Explanation
Anaerobic metabolism, such as glycolysis and fermentation, occur in the cellular cytoplasm. The products of glycolysis are transported to the mitochondria where they undergo Krebs cycle (in mitochondrial matrix) and oxidative phosphorylation (on the inner mitochondrial membrane). Both Krebs cycle and oxidative phosphorylation require oxygen and are, therefore, called aerobic metabolism.
Anaerobic metabolism occurs in the __________; fermentation occurs in the __________.
cytoplasm . . . cytoplasm
cytoplasm . . . mitochondria
mitochondria . . . cytoplasm
mitochondria . . . mitochondria
Explanation
Anaerobic metabolism, such as glycolysis and fermentation, occur in the cellular cytoplasm. The products of glycolysis are transported to the mitochondria where they undergo Krebs cycle (in mitochondrial matrix) and oxidative phosphorylation (on the inner mitochondrial membrane). Both Krebs cycle and oxidative phosphorylation require oxygen and are, therefore, called aerobic metabolism.