EXAM 2 Mastering Biology
How does oxidative phosphorylation occur?
-Occurs under the action of ATP synthase -occurs when electrons move through an ETC and produce a proton-motive force that drives ATP synthase
How does substrate-level phosphorylation occur?
-occurs under the action of pyruvate kinase an phosphoglycerate kinase -occurs when enzymes remove a high-energy phosphate from a substrate and directly transfer it to ADP
1. When a compound donates (loses) electrons, that compound becomes __________. Such a compound is often referred to as an electron donor. 2. When a compound accepts (gains) electrons, that compound becomes __________. Such a compound is often referred to as an electron acceptor. 3. In glycolysis, the carbon-containing compound that functions as the electron donor is __________. 4. Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called __________. 5. __________ is the compound that functions as the electron acceptor in glycolysis. 6. The reduced form of the electron acceptor in glycolysis is __________.
1. oxidized 2. reduced 3. glucose 4. pyruvate 5. NAD+ 6. NADH
Atmospheric pressure at sea level is equal to a column of 760 mm Hg. Oxygen makes up 21 percent of the atmosphere by volume. The partial pressure of oxygen (PO2) in such conditions is _____.
160 mmHg
How many NADH molecules are produced in glycolysis and pyruvate processing?
2 in glycolysis 2 in pyruvate processing
At the summit of a high mountain, the atmospheric pressure is 380 mm Hg. If the atmosphere is still composed of 21percent oxygen, then the partial pressure of oxygen at this altitude is about _____.
80 mmHg
Early estimates suggested that the oxidation of glucose via aerobic respiration would produce 38 ATP. Why do biologists now think this amount of ATP per molecule of glucose is not achieved in cells?
A cell will not produce this much ATP, because the proton-motive force is used in other transport steps and because of other issues that may reduced the overall efficiency.
Which of the following are products of the light reactions of photosynthesis that are utilized in the Calvin cycle?
ATP and NADPH
Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?
ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.
Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?
ATP, pyruvate, and NADH ATP is the main product of cellular respiration that contains energy that can be used by other cellular processes. Some ATP is made in glycolysis. In addition, the NADH and pyruvate produced in glycolysis are used in subsequent steps of cellular respiration to make even more ATP.
Which of the following aquariums would require the most air bubbled in to maintain oxygenation of the water: Aquarium A with warm water and some fish; Aquarium B with cold water, some fish, and some algae; or Aquarium C with warm salt water and some fish?
Aquarium C Warm temperature, lack of photosynthetic organisms, and salt all reduce water oxygenation.
How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)
Both electron transport and ATP synthesis would stop. Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. Without O2, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation. In addition, without O2 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.
Compare and contrast substrate-level phosphorylation and oxidative phosphorylation. What do they have in common?
Both processes produce ATP from ADP and Pi
How is cellular respiration regulated?
By ATP through feedback inhibition. High levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. This decreases the rate of cellular respiration and ATP production
Which gas does this apply to? Waste product of cellular respiration Net diffusion from lung capillaries to alveoli Net diffusion from body tissues to blood Sometimes transported as bicarbonate
Carbon dioxide Carbon dioxide is transported either in the plasma, bound to hemoglobin, or in the form of bicarbonate.
_____ is the most abundant organic compound on Earth
Cellulose
Predict how Antarctic icefish can transport enough oxygen in their blood to meet their needs even though they lack hemoglobin.
Cold water carries more oxygen than warm water does. The oxygen is simply dissolved in the blood.
Sort the statements into the appropriate bin depending on whether or not they correctly describe some aspect of substrate-level phosphorylation in glycolysis.
Correct: An enzyme is required in order for the rxn to occur One of the substrates is a mlc derived from the breakdown of glucose A bond must be broken b/w an organic mlc and phosphate before ATP can form Incorrect: The enzymes involved in ATP synthesis must be attached to a membrane to produce ATP The phosphate group added to ADP to make ATP comes from free inorganic phosphate ions.
Countercurrent exchange in the fish gill helps to maximize ________.
Extraction of oxygen from the water
What do stomata do?
Facilitate gas exchange
NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2?
Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor. Electrons derived from the oxidation of FADH2 enter the electron transport chain at Complex II, farther down the chain than electrons from NADH (which enter at Complex I). This results in fewer H+ ions being pumped across the membrane for FADH2 compared to NADH, as this diagram shows. Thus, more ATP can be produced per NADH than FADH2.
During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization?
Glucose utilization would increase a lot. ATP made during fermentation comes from glycolysis, which produces a net of only 2 ATP per glucose molecule. In contrast, aerobic cellular respiration produces about 30 ATP per glucose molecule. To meet the same ATP demand under anaerobic conditions as under aerobic conditions, a cell's rate of glycolysis and glucose utilization must increase about 15-fold.
Which of the following sequences correctly represents the flow of electrons during photosynthesis? NADPH → O2 → CO2 NADPH → chlorophyll → Calvin cycle NADPH → electron transport chain → O2H2O → photosystem I → photosystem II H2O → NADPH → Calvin cycle
H2O → NADPH → Calvin cycle
C6H12O6 (glucose) + 6 O2 → 6 CO2 + 6 H2O Where is most of the water in this reaction produced?
In the ETC
Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. What is the explanation for this observation?
In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration NAD+ couples oxidative phosphorylation to acetyl CoA formation. The NAD+ needed to oxidize pyruvate to acetyl CoA is produced during electron transport. Without O2, electron transport stops, and the oxidation of pyruvate to acetyl CoA also stops because of the lack of NAD+.
Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. Why?
In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration.
Where does the citric acid cycle occur in eukaryotes?
In the matrix of mitochondria
What are the net inputs and outputs of oxidative phosphorylation?
Input: ADP, O2, NADH Output: water, ATP, NAD+ In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.
What are the net inputs and outputs of the citric acid cycle?
Inputs: acetyl CoA, NAD+. ADP Output: NADH, ATP, coenzyme A, CO2 The two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. In addition, one molecule of ATP is produced
What are the net inputs and net outputs of glycolysis?
Inputs: glucose, NAD+, ADP Outputs: for each 6-C mlc of glucose two molecules of pyruvate (3-C), 2 ATP, and 2 NADH are made
In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve?
It increases the surface for oxidative phosphorylation.
Pyruvate, a three-carbon molecule, is processed into acetyl CoA, a two-carbon molecule. What happened to the missing carbon?
It is lost as carbon dioxide (CO2)
What purpose does fermentation serve?
It regenerates NAD+ from NADH to keep glycolysis going in the absence of oxygen. Fermentation is unlikely to occur when oxygen is available as the final electron acceptor at the end of the electron transport chain.
Match the product of pyruvate metabolism with the condition under which it is produced. Lactate: Ethanol: Acetyl CoA:
Lactate = fermentation in human muscle Ethanol = fermentation in yeast and bacteria Acetyl CoA: aerobic oxidation
Which feature is common to gills, lungs, and tracheae? Delivering oxygen directly to cells without a circulatory system Dead space Countercurrent exchange mechanism Large surface area
Large surface area allows for better gas exchange
What would happen to the proton gradient and ATP production after a drug has poisoned the enzyme that combines acetyl CoA and oxaloacetate to form citrate?
Less NADH production would create to a weaker proton gradient and less ATP production.
Which statement best describes what happens during the redox reaction between NADH and Complex I of the electron transport chain? See Section 9.5 A)NADH is oxidized as a pair of electrons, which are transferred to the ETC and 4 four H+ are pumped into the intermembrane space. B)Two electrons from NADH are used to reduce oxygen gas (O2), which picks up two H+ form from the matrix to produce water. C)NADH is oxidized by FADH2 which is then immediately oxidized in complex Complex II. D)Ubiquinone receives two electrons from NADH and then moves throughout the hydrophobic interior of the ETC membrane where it is oxidized by complex Complex II.
NADH is oxidized as a pair of electrons, which are transferred to the ETC and 4 four H+ are pumped into the intermembrane space.
What are the net inputs and outputs of acetyl CoA formation?
Net input: pyruvate, NAD+, coenzyme A Output: acetyl CoA, NADH, CO2 Pyruvate is oxidized to acetyl CoA, NAD+ is reduced to NADH
Which of the following classes of macromolecules always contains a carbohydrate portion?
Nucleic acids Recall that nucleic acids always contain a pentose sugar
Which gas is this described by? Required for cellular respiration net diffusion from alveoli to lung capillaries
Oxygen
Which gas does this describe? Transported by hemoglobin Enters alveoli during inhalation
Oxygen and carbon dioxide
An investigator exposes chloroplasts to 700-nm photons and observes low O2 production, but high ATP production. Which of the following best explains this observation?
Photosystem II is not splitting water, and the ATP is being produced by cycling electrons via photosystem I. The wavelength of light would fully excite PS I but is less likely to excite PS II, resulting in cyclic electron flow since few electrons could be harvested from water by PS II.
Predict how the thickness of cuticle and the number of stomata differ in plants from wet habitats versus dry habitats.
Plants from wet habitats: thin cuticle, relatively large # of stomata Plants from dry habitats: thick cuticle, relatively few stomata
What are the reactants and products in the anaerobic reduction of pyruvate during lactic acid fermentation?
Reactants: pyruvate, NADH Products: NAD+, lactate
What does the cuticle do?
Reduces water loss
When the protein gramicidin is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). If gramicidin is added to an actively respiring muscle cell, how would it affect the rates of electron transport, proton pumping, and ATP synthesis in oxidative phosphorylation? (Assume that gramicidin does not affect the production of NADH and FADH2 during the early stages of cellular respiration.)
Remains the same: proton pumping rate rate of oxygen uptake electron transport rate Decreases (or goes to zero): rate of ATP synthesis, size of the proton gradient Gramicidin causes membranes to become very leaky to protons, so that a proton gradient cannot be maintained and ATP synthesis stops. However, the leakiness of the membrane has no effect on the ability of electron transport to pump protons. Thus, the rates of proton pumping, electron transport, and oxygen uptake remain unchanged.
What is the mechanism of ATP synthesis in glycolysis?
Substrate-level phosphorylation In substrate-level phosphorylation, an enzyme transfers a phosphate group from one molecule (an intermediate in the breakdown of glucose to pyruvate) to ADP to form ATP.
What is the man coupling among the stages of cellular respiration accomplished by?
The main coupling among the stages of cellular respiration is accomplished by NAD+ and NADH. In the first three stages, NAD+ accepts electrons from the oxidation of glucose, pyruvate, and acetyl CoA. The NADH produced in these redox reactions then gets oxidized during oxidative phosphorylation, regenerating the NAD+ needed for the earlier stages.
Which of the following statements correctly identifies why fermentation alone won't keep cells alive?
The oxidation of glucose via cellular respiration has the potential yield of 29 ATP while the oxidation of glucose via fermentation yields only 2 ATP. Cellular respiration is much more efficient at harvesting potential energy from glucose
Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water). Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.)
The rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease
Which of the following respiratory systems is NOT closely associated with the blood supply? the skin of an earthworm the tracheal system of an insect the gills of a fish the lungs of a vertebrate
The tracheal system of an insect
The energy of electron transport serves to move (translocate) protons to the outer mitochondrial compartment. How does this help the mitochondrion produce ATP?
The translocation of protons sets up the electrochemical gradient that drives ATP synthesis in the mitochondria.
Why are fermentation reactions important for cells?
They regenerate NAD+ so that glycolysis can continue to operate.
During the citric acid cycle FADH2 and NADH are produced. What purpose do these molecules serve in the electron transport chain (ETC)?
They serve as electron donors in the ETC.
Cyanide (C≡N−) blocks complex IV of the electron transport chain. Suggest a hypothesis for what happens to the ETC when complex IV stops working.
When complex IV is blocked, electrons can no longer be transferred to oxygen and cellular respiration stops. Fermentation could keep glycolysis going, but it is unable to fuel energy needs over the long term. The low production of ATP would result in systemic cell death, those cells that lack the capacity for fermentation dying first.
Glycogen is _____.
a polysaccharide found in animals
Even though plants cells photosynthesize, they still use their mitochondria for oxidation of pyruvate. This will occur in _____.
all cells all the time
During pyruvate processing, two carbons from pyruvate combine with ____
coenzyme A One carbon of the three-carbon pyruvate becomes oxidized to CO2 and the remaining two carbons (acetate) combine with coenzyme A to form acetyl coenzyme A.
Match each stage of cellular respiration with the cellular location in which it occurs glycolysis acetyl CoA formation citric acid cycle oxidative phosphorylation
cytosol mitochondrial matrix mitochondrial matrix inner mitochondrial membrane
Which metabolic pathway is common to both cellular respiration and fermentation?
glycolysis
What type of bond is formed between two sugars in a disaccharide?
glycosidic linkage
glucose + glucose —> _____ by _____.
maltose + water ... dehydration synthesis
Energy released by the electron transport chain is used to pump H+ into which location in eukaryotic cells?
mitochondrial intermembrane
During cellular respiration, acetyl CoA accumulates in which location?
mitochondrial matrix
Glycolysis is a series of ___ reactions that occurs in the _____ of cells
ten; cytoplasm
In mitochondrial electron transport, what is the direct role of O2?
to function as the final electron acceptor in the electron transport chain
For each molecule of glucose processed during glycolysis, the net yield is ____
two molecules of NADH, two of ATP, and two of pyruvate
What is the correct order of processes involving the movement of oxygen from the environment to mitochondria in vertebrates?
ventilation, circulation, cellular respiration